■fix, VHO GRAY HERBARIUM mar\: 26 m Newsletter of the Hawaiian Botanical Society Volume 40 Number 4 October-December, 2001 ISSN: 1523-7338 Lobelia gloria-mantis In This Issue A Review of the Genetic and Evolutionary Effects of Plant Invasions by Charles Chimera 25 Association of Armillaria mellea with Mamane Decline at Pu‘u La(au by Donald E. Gardner and Edu- ardoE. Trujillo 33 Hybridization and the Potential Consequences for Rare Plant Species by Karen Brimacombe 35 Minutes of the Hawaiian Bo- tanical Society: October - December 2001 40 Treasurer’s Report: January- December 2000 42 A Review of the Genetic and Evolutionary Effects of Plant Invasions Charles Chimera Department of Botany University of Hawai‘i at Manoa Honolulu, HI 96822 Invasive species are now recognized as a worldwide problem by threat- ening global biodiversity (Heywood, 1989; Lonsdale, 1999), contributing to major environmental damage and economic losses (Pimentel et al., 2000), and altering ecosystem structure and function through their impacts on soil nutrient levels (Vitousek and Walker, 1989), altered fire regimes (D’ Antonio and Vitousek, 1992), native seedling recruitment (Richardson et al., 1989; Walker and Vitousek, 1991) and reduced stream-flow (van Wilgen et al., 1992; van Wilgen et al., 1996). Mark Williamson (1996) published Biological Invasions, a book reviewing current literature that addressed a broad range of issues pertaining to biological invasions of both plants and animals. One chapter of the book dealt with the genetic and evolutionary effects of biological invasions, and focused its review on two main points: 1) genetics may affect the success of invaders, and evo- lution may occur following invasion; and 2) studies of biological inva- sions can be used to better understand risks associated with introducing new species and genotypes and in releasing genetically engineered organ- isms. Williamson (1996) gives examples of how genetics plays roles in inva- sions. He states that individual genes or groups of genes could have an effect on invasion success, and points to the differential success of Impa- tiens capensis versus I. noli-tangere in England as one such example. He Continued on Page 27 26 Newsletter of the Hawaiian Botanical Society Published by the Hawaiian Botanical Society which was founded in 1924 to... “...advance the science of botany in all its applications, encourage re- search in botany in all its phases, promote the welfare of its members and develop the spirit of good fel- lowship and cooperation among them. ” Any person interested in the plant life of the Hawaiian Islands is eligible for membership. Information may be obtained from the Society at: c/o Department of Botany 3190 Maile Way University of Hawai‘i Honolulu, HI 96822 Membership The Society year is from December 1 through November 30 Membership Cost/year Individual $10.00 Student $5.00 Family $12.00 Life (individuals only) $180.00 Institutional Rate $20.00 Honorary and Life Members pay no further dues. Executive Committee President Brandon Stone Vice-President Don Gardner (USGS-BRD & UH Department of Botany) Treasurer Ron Fenstemacher (Ho ‘okahe Wai Ho ‘olu ‘ ina ) Secretary Chuck Chimera (UH Department of Botany) Directors Susan Ching-Harbin (UH Department of Botany) Jeff Preble (Pacifica Tropicals) Committees Appointed by the Executive Committee Membership Carol Annable, Co-Chair Alvin Yoshinaga, Co-Chair Lyon Arboretum Newsletter Cliff Morden, Editor UH-Botany/CCRT Don Gardner, Assist. Ed. UH Botany Rob Anderson, Layout Specialist UH Botany Conservation Steve Montgomery Independent Consultant Undergraduate Grants Leilani Durand UH-Botany Alvin Chock USDA-APHIS-IS/UH-Botany Science Fair Karen Shigematsu, Chair Lyon Arboretum Winona Char Char and Associates Native Plants Alvin Yoshinaga, Chair UH-CCRT John Obata Bishop Museum Karen Shigematsu Lyon Arboretum Roger Sorrell Volume 40(4), 2001 27 Continued from page 25 indicates that that gene frequencies can also change dur- ing the course of an invasion, using the example of rab- bits adapting to the myxoma virus. He cautions about over-emphasizing the importance of genetic changes in theorizing about the establishment and success of inva- sive species without conclusive proof, but recognizes that all introduced invasive species will eventually un- dergo genetic changes in the long run. The important and more immediate question concerning invasive species and their genetic and evolutionary effects is whether or not identifiable genetic differences exist prior to inva- sions that contribute to invasion success or whether they occur during an invasion and result in the rapid spread and proliferation of the exotic species. Other possibilities include genetic changes in invasive species over a longer period of time, well after a species has already become established. In addition, the implications of genetically engineered organisms as potential invasive species are discussed and associated concerns are raised. The fol- lowing sections will address these issues and provide ex- amples from the current body of literature. Genetic Differences Allowing Invasion Williamson (1996) uses examples of closely related species of Impatiens, sparrows, Rhizobium spp., and rats to demonstrate the importance of genetic differences be- tween invaders and non-invaders. In the case of the sparrows and rats, he attributes the differential success of the invaders versus the non-invaders to their greater abundance, wider ranges in their native region and there- fore, greater genetic diversity and adaptability to more environments. In contrast, single or a few gene differ- ences contribute to the success of Rhizobium invasions on different legume species (Young and Johnston, 1989). There are many examples in the Hawaiian flora of na- tive genera with non-native congeners that have become established in the islands. Specific examples include the native Bidens species (Asteraceae) and the invasive Bidens pilosa, and native and non-native species of Heliotropium (Boraginaceae), Chenopodium (Chenopodiaceae), Ipomoea (Convolvulaceae), Acacia (Fabaceae), Abutilon (Malvaceae), Boerhavia (Nyctaginaceae) Argemone (Papaveraceae), Panicum (Poaceae), and Rubus (Rosaceae) among others (Wagner et ah, 1990). Obviously, these species are genetically different from one another to various degrees, but whether or not these genetic differences contribute to the abundance and spread of the non-native taxa versus the more localized distribution of most of the native species is unknown. Barrett (1987) demonstrated that genetic diversity was commonly higher in wide ranging invasive species than related endemic species, and Meekins et al. (2000) hypothesized that the same might be true for the widespread and invasive Alliaria petiolata (Brassicaceae) if compared to A. brachycarpa, a nar- rowly distributed species endemic to the Caucasus mountains. Albert et al., (1997) identified genetic differ- ences between the invasive, non-native Carpobrotus edulis (Aizoaceae) and the less aggressive, presumed na- tive C. chilensis in California, and discuss hybridization between the taxa (discussed in the next section). Lam- brinos (2001) looked at the invasion histories of two re- lated non-native species in California, the sexually repro- ducing Cortaderia selloana and the asexually reproduc- ing, agamospermous C. jubata. Although similar in morphology and introduced at approximately the same time, C. selloana' s invasiveness has increased with time, and it has expanded at twice the rate as the asexual C. jubata. Lambrinos (2001) attributes this difference to the ability of the sexual and genetically diverse C. sel- loana to adapt to a greater diversity of landscapes than the asexual C. jubata, with its reduced amount of genetic diversity. The absence of sexual reproduction is not always a detriment to invasions, however, as evidenced by the apomictic African grass Pennisetum setaceum, with high phenotypic plasticity, a variable chromosome number (2n = 18, 27, 54) and the greatest altitudinal range of any grass species in the Hawaiian Islands (Wagner et al., 1990; Williams et al., 1995). Nevertheless, several ex- amples indicate that the reduced genetic diversity of colonizing species could prevent the expansion of invad- ers into a wider range of habitats than might otherwise be possible. This was demonstrated by Jain and Martins (1979) in populations of Trifolium hirtum invading Cali- fornia, and by Lambrinos (2001) with Cortaderia jubata. Radford and Cousens (2000), in comparing the invasive species Senecio madagascariensis to the non-invasive 5. lautus (Asteraceae) in Australia, determined that species performance differences were probably not genetically fixed which was contrary to other findings of this sec- tion. Instead, they seem to have responded to environ- mental differences. They conclude that invasions must be looked at on a case-by-case basis and that the combi- nation of unique plant genotypes and environments pre- vent general predictions about which species will be- come invasive. Nevertheless, several authors have attempted to iden- tify generalizations about the genetics of invasive plants. Bennett et al. (1998) compared DNA amounts in 156 species of weeds in the British Isles with 2685 non- invasive species and found that DNA amounts per ge- nome in weeds were smaller than in other species. They 28 Newsletter of the Hawaiian Botanical Society state that these findings could either imply that selection exists for smaller DNA amounts and genome size in weeds, or that smaller DNA amounts and genome sizes are useful preadaptations for invasive species. Bennett et al. (1998) also found increased levels of polyploidy in 116 weed species compared to 2357 non-invasive spe- cies, results that could reflect increased genetic variation in the invaders. Finally, Rejmanek (1996, 1999) and Grotkopp et al. (1998) also point to a small genome size and suggest that it is the result of selection for a reduced generation time that, among other factors, could contrib- ute to a plant’s invasiveness. Genetic Changes During Invasion Some species appear to demonstrate a lag time after colonization before they become invasive. Williamson (1996) states that, without common garden experiments, it is not possible to know if a plant’s change in invasive- ness after a lag period is due to a modification in habitat, or if some genetic change triggered the invasion. He questions whether evidence exists for genetic changes that promote invasions, and states that hybridization events, resulting in invasions or genetic pollution of na- tive species, provide the only concrete evidence of such genetic changes. Other authors (Sun, 1997; Crooks and Soule, 1999) state that the lag times sometimes wit- nessed could be due to a genetic lag or period in which population numbers are too low. They believe that both a greater number of introductions in the future, or indi- viduals with outbreeding systems, can overcome this lag more rapidly by providing an infusion of new alleles or genotypes. In one example, Dietz et al. (1999) state that anthropogenic disturbance contributes to greater gene flow between populations of the invasive Bunias orien- tals (Brassicaceae), and that this increase in genetic di- versity has made this species more adaptable to a broader range of changing habitats associated with such distur- bance regimes. They suggest that further research should explore whether greater genetic diversity of foun- der populations results in greater plant fitness later in the invasion process. Morrison and Molofsky (1998) ad- dress this issue by examining different genotypes of the invasive grass Phalaris arundinacea, and conclude, “high levels of genetic diversity increase the likelihood that a particular genotype will flourish and spread into new areas.” Williamson (1996), as previously stated, points to hy- bridization events as more concrete evidence for genetic changes leading to invasions and the genetic conse- quences of such invasions. He and other authors (Thompson, 1991; Ellstrand and Schierenbeck, 2000) use the example from England of Spartina anglica (Poaceae), an allotetraploid hybrid between the native S. maritima and the North American S. alternijlora. The hybrid is more common and vigorous than native Spartina species in England, Scotland and Ireland, where it grows in crop-like monotypic stands. Albert et al. (1997) and Gallagher et al. (1997) use morphological and allozyme evidence to demonstrate hybridization be- tween the invasive Carpobrotus edulis (Aizoaceae) and the presumably native C. chilensis in California. They state that C. edulis “is the more likely recipient of intro- gressed genes than C. chilensis ” and that the ecological attributes of the hybrids are more similar to C. edulis. Because both the invader and the hybrid tend to domi- nate native communities to different degrees (Weber and D’ Antonio, 1999), one of the implications of these hy- bridization events is that introgression could be develop- ing a novel genotype with greater potential to invade and modify ecosystems, and could also result in genetic as- similation of the native species. Ellstrand and Schierenbeck (2000) discuss the devel- opment of novel genotypes, as well as increased genetic variation, fixed heterosis and the dumping or elimination of genetic load as possible reasons why hybridization events could lead to more vigorous, and therefore, more invasive weeds. They proceed to give 28 such examples of hybridization events resulting in the development of invasive taxa or invasive lineages. They further address the concept that “hybridization” between different or dis- tant populations of the same species may act in the same way as hybridization between different taxa, resulting in more fit offspring better able to invade a wider range of habitats. Barrett and Husband (1990) also mention this as a factor leading to the greater genetic diversity and invasiveness of Echium plantagineum, a noxious weed in Australia that resulted from gene flow (i.e., “hybridization”) between multiple introduced popula- tions. Of further concern is the possibility that hybridization among congeners may lead to genetic assimilation or “pollution” of native species (Williamson, 1996). Huxel (1999) claims that invaders may “genetically swamp” native species through increased pollen production or increased fertility, and that this in turn can lead to rapid replacement of the native species by the invader and hy- brid populations. Manchester and Bullock (2000) also mention these consequences in discussions on hybridiza- tion. Gallagher et al. (1997) state that hybridization be- tween native and non-native Carpobrotus species “threaten the genetic integrity of the native species.” Further examples of hybridization between native and Volume 40(4), 2001 29 non-native taxa, implying possible assimilation of the native, are given by Daehler and Strong (1997a) and Anttila et al. (1998) for crosses between the introduced Spartina alterniflora and the native S. foliosa in Califor- nia. Examples from Hawai‘i are given by Randell (2000) between the native Rubus hawaiensis and the in- troduced R. rosifolius as well as by Wagner et al. (1990) between the native poppy Argemone glauca and the in- troduced A. mexicana. The consequences of these hy- bridization events are yet to be determined. Neverthe- less, this issue is another cause for concern when dealing with conservation and protection of Hawaii’s rare flora, especially when considering the number of native taxa with non-native congeners currently established in the Hawaiian Islands, as well as with the continuous intro- duction of new taxa by the agricultural and horticultural industries. Perhaps, because of this potential for hybridi- zation, particular attention should be paid to non-native plant taxa with native congeners in development of screening systems for the Hawaiian Islands as well as for other regions of the world. In contrast to all of the preceding examples, Williams et al. (2000) assessed the genetic risks of introducing new non-native plant taxa into New Zealand and con- cluded that “genetic pollution” of native taxa was only a minimal threat. As more research is conducted, and global commerce further accelerates the movement of, and contact between, previously isolated congeneric taxa, more examples and consequences of hybridization will undoubtedly be discovered. Genetic and Evolutionary Changes After Invasion Williamson (1996) states that although invasions occur quickly, the evolution of the invader is slow and may be undetectable for a long period of time. He further claims that significant ecological changes following invasions are the exception rather than the rule. Williamson and Fitter (1996) mention the speculative case of Epilobium angustifolium, a species that changed from a rare native to a widespread invader early in the century, but admit that genetic evidence is lacking. Blossey and Notzold (1995) proposed the “evolution of increased competitive ability” hypothesis to explain the phenomenon that alien species are often larger and produce more seeds in their introduced versus their na- tive range, as observed by Crawley (1987). This hy- pothesis states that, in the absence of herbivores, selec- tion favors genotypes that have quicker growth rates, greater seed production, larger leaves, or other competi- tive abilities over genotypes that devote energy and re- sources to defense against herbivores. They use the ex- ample of Lythrum salicaria, an invasive plant in North America that, in common garden studies, has higher growth rates and produces more biomass than plants from the native range of Switzerland. However, most studies that address the hypothesis of increased competitive ability do not support it. Willis et al. (1999) tried to corroborate the hypothesis by investi- gating whether introduced L. salicaria plants were more susceptible to herbivores as a result of this shift in re- sources, but found little evidence to support the conclu- sions of Blossey and Notzold (1995). Willis et al. (2000) examined differences between four weeds present in Australia and New Zealand and from their native ranges, and similarly found little evidence that increased plant size is genetically determined. Daehler and Strong (1997b) did find reduced herbivore resistance in intro- duced Spartina alterniflora populations, but state that this could be due to founder effects or herbivore prefer- ence rather than evolution of competitiveness in growth. In fact, they actually found that plants with the more rapid growth rates had greater herbivore resistance, in contrast to the findings of Blossey and Notzold (1995). In yet another study, Thebaud and Simberloff (2001) looked at non-native plant species introduced from Cali- fornia and the Carolinas into Europe, and European spe- cies introduced into California and the Carolinas, and again found no tendency for the plants to be larger in the non-native regions. They suggest that, when introduced taxa are larger, it may be due to the absence of herbi- vores from their native ranges, but that each species must be looked at on a case-by-case basis. The underlying conclusion, reiterated by many other authors, is that gen- eralizations about invasive species are difficult to sup- port. In one example that does suggest genetic changes oc- curring during and after invasions, Lambrinos (2001) found that populations of Cortaderia selloana have changed morphologically over the past 80 years and be- lieve this is because of genetic adjustments since their introduction into California. Innumerable examples exist of invasive plant species in the Hawaiian Islands whose success is frequently attributed to some form of ecologi- cal release from their co-evolved herbivores, pathogens and other competitive elements. This presumption is of- ten the driving force behind the search for biocontrol agents of some of the more aggressive and serious invad- ers. Whether invasive success is due to phenotypic changes as a result of ecological release, the “evolution of (an) increased competitive ability,” some combination of the two, or neither should be examined for each spe- 30 Newsletter of the Hawaiian Botanical Society cies, and such assumptions thoroughly tested as part of the investigation into biocontrol. Further research exam- ining differences between introduced plants in their na- tive and non-native ranges throughout the world will likely shed more light on this concept of genetic changes occurring after invasions. Genetically Engineered Plants Williamson (1996) addresses the concerns associated with the release of genetically engineered plants and states that invasions often result when a plant finds itself in a new environment. He concludes that since all envi- ronments are essentially new to a genetically engineered plant, extreme caution must be taken when releasing them into the environment. He also warns that since ge- netically engineered plants are generally commercial products, there is an increased likelihood that they will be widely distributed and essentially uncontrollable if they do start to escape from cultivation. Other authors point to several cases of engineered genes spreading from crop plants into wild populations (Klinger and Ell- strand, 1994, Bergelson et al., 1998), and suggest that engineered genes in crops may spread more than wild genes in certain weeds (Bergelson, 1994; Bergelson et al., 1998). Warwick et al. (1999) suggest that genetically engineered plants can change weed communities and populations by escape and invasion of the genetically engineered plants themselves, by hybridization with and selective introgression of engineered genes into weeds or wild plants, and by genetic changes in unrelated popula- tions of plant species resulting from environmental changes, such as the development of herbicide resistant crops and/or weeds. For these reasons, and because of the level of unpredictability of weed invasions in gen- eral, several authors (Parker and Kareiva, 1996; War- wick et al., 1999; Paltridge, 2000; Kjellsson and Strandberg, 2001) make suggestions and offer guidelines and protocols for the development, monitoring and re- lease of genetically engineered plants, with the intention of minimizing these potential risks. Conclusion With increasing numbers of studies being conducted, knowledge about the genetics of invasive species, from genetically “ideal” invaders to changes in invasive spe- cies over time, is rapidly growing and will continue to provide insights and improve powers of prediction and management of invaders. Although no concrete rules have been developed as a result of the genetic research being conducted on invasive species, general patterns and trends are starting to emerge, and previously unfore- seen consequences of invasions are now being identified at the molecular as well as the ecological level. Genetic approaches to the study of invasive species are likely to become an increasingly important tool in understanding the processes of invasion, especially with expanding global commerce and movement of plants and animals around the world, and with the growing numbers of ge- netically engineered crops being developed and utilized. Although Williamson (1996) states that invasions are fast and evolution is slow, the factors that affect evolu- tion of species (particularly gene flow and “mutation” via genetic engineering) are being altered by humans at a rapid pace, and molecular techniques, along with more studies of quantitative ecological genetics, may provide the best method of detecting and understanding the ge- netic changes and consequences of current and future invasions. Literature Cited Albert, M.E., C.M. D’Antonio, and K. Schierenbeck. 1997. Hybridization and introgression in Carpobro- tus spp. (Aizoaceae) in California. I. Morphological evidence. American Journal of Botany 84(8): 896- 904. Anttila, C.K., C.C. Daehler, N.E. Rank and D.R. Strong. 1998. Greater male fitness of a rare invader (Spartina alterniflora, Poaceae) threatens a common native ( Spartina foliosa ) with hybridization. Ameri- can Journal of Botany 85( 1 1 ): 1 597- 1601. Barrett, S.C.H. 1987. Genetics and evolution of agricul- tural weeds. Pp. 57-75 in M.A. Altieri, M. Liebman (eds.). Weed management in agroecosystems: eco- logical approaches. CRC, Boca Raton, Florida. Barrett, S.C.H., and B.C. Husband. 1990. The genetics of plant migration and colonization. Pp. 254-277 in A. H.D. Brown, M.T. Clegg, A.L. Kahler, and B.S. Weir (eds.). Plant population genetics, breeding, and genetic resources. Sinauer, Sundlerland, Massachu- setts. Bennett, M.D., EJ. Leitch and L. Hanson. 1998. DNA amounts in two samples of angiosperm weeds. An- nals of Botany 82(Supplement A): 121-134. Bergelson, J. 1994. Changes in fecundity do not predict invasiveness: a model study of transgenic plants. Ecology 75(1): 249-252. Bergelson, B., C.B. Purrington and G. Wichmann. 1998. Promiscuity in transgenic plants. Nature 395: 25. Blossey, B. and R. Notzold. 1995. Evolution of increased competitive ability in invasive nonindigenous plants: a hypothesis. Journal of Ecology 83: 887-889. Crawley, M.J. 1987. What makes a community invasi- Volume 40(4), 2001 31 ble? Pp. 429-453 in A.J. Gray, M.J. Crawley, and P. J. Edwards (eds.). Colonization succession and sta- bility. Blackwell Scientific Publications, Oxford. Crooks, J.A., and M E. Soule. 1999. Lag times in popu- lation explosions of invasive species: causes and implications. Pp. 103-125 in O.T. Sandlund, P.J. Schei, and A. Viken (eds.). Invasive species and biodiversity management. Kluwer Academic Pub- lishers, Dordrecht, Netherlands. Daehler, C.C. and D.R. Strong. 1997a. Hybridization between introduced smooth cordgrass ( Spartina al- terniflora\ Poaceae) and native California cordgrass (S. foliosa) in San Francisco Bay, California, USA. American Journal of Botany 84(5): 607-61 1 . Daehler, C.C. and D.R. Strong. 1997b. Reduced herbi- vore resistance in introduced smooth cordgrass (Spartina alterniflora) after a century of herbivore- free growth. Oecologia 1 10(1): 99-108. D’Antonio, C.M. and P.M. Vitousek. 1992. Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annual Review of Ecological Sys- tems 23: 63-87. Dietz, H, M. Fischer, and B. Schmid. 1999. Demo- graphic and genetic invasion history of a 9-year-old roadside population of Bunias orientalis L. (Brassicaceae). Oecologia 120: 225-234. Ellstrand, N.C. and K.A. Schierenbeck. 2000. Hybridi- zation as a stimulus for the evolution of invasive- ness in plants?. Proceedings of the National Acad- emy of Sciences 97(13): 7043-7050. Gallagher, K.G., K.A. Schierenbeck, and C.M. D’Anto- nio. 1997. Hybridization and introgression in Car- pobrotus spp. (Aizoaceae) in California IE Al- lozyme evidence. American Journal of Botany 84 (8): 905-911. Grotkopp, E., R. Stoltenberg, M. Rejmanek, and T. Rost. 1998. The effect of genome size on invasive- ness. American Journal of Botany 85(Supp!ement): 34. Heywood, V.H. 1989. Patterns, extents and modes of invasions by terrestrial plants. Pp. 31-60 in J.A. Drake, H.A. Mooney, F. di Castri, R.H. Groves, F. J. Kruger, M. Rejmanek, and M. Williamson, (eds.). Biological Invasions: a global perspective. John Wiley, Chichester, UK. Huxel, G.R. 1999. Rapid displacement of native species by invasive species: effects of hybridization. Bio- logical Conservation 89: 143-152. Jain, S.K. and P.S. Martins. 1979. Ecological genetics of the colonizing ability of rose clover ( Trifolium hirtum All.). American Journal of Botany 66: 361- 366. Kjellsson, G. and M. Strandberg. 2001. Monitoring and surveillance of genetically modified higher plants: guidelines for procedures and analysis of environ- mental effects. Birkhauser Verlag AG, Basel, Swit- zerland. Klinger, T. and N.C. Ellstrand. 1994. Engineered genes in wild populations: fitness of weed-crop hybrids of Raphanus sativus: Ecological Applications 4: 117- 120. Lambrinos, J.G. 2001. The expansion history of a sex- ual and asexual species of Cortaderia in California, USA. Journal of Ecology 89: 88-98. Lonsdale, W.M. 1999. Global patterns of plant inva- sions and the concept of invisibility. Ecology 80(5): 1522-1536. Manchester, S.J. and J.M. Bullock. 2000. The impacts of non-native species on UK biodiversity and the effectiveness of control. Journal of Applied Ecol- ogy 37: 845-864. Meekins, J.F., H.E. Ballard, Jr. and B.C. McCarthy. 2000. Genetic variation and molecular biogeogra- phy of the North American invasive plant species (Alliaria petiolata, Brassicaceae). International Journal of Plant Science 162(1): 161-169. Morrison, S.L. and J. Molofsky. 1998. Effects of geno- types, soil moisture, and competition on the growth of an invasive grass, Phalaris arundinacea (reed canary grass). Canadian Journal of Botany 76: 1939-1946. Paltridge, N.G. 2000. Applications for molecular biol- ogy in weed management. Plant Protection Quar- terly 15(2): 50-56. Parker, l.M. and P. Kareiva. 1996. Assessing the risks of invasion for genetically engineered plants: ac- ceptable evidence and reasonable doubt. Biological Conservation 78: 193-203. Pimentel, D., L. Lach, R. Zunigaand D. Morrison. 2000. Environmental and economic costs of nonin- digenous species in the Unites States. BioScience 50(1): 53-65. Radford, I.J. and R.D. Cousens. 2000. Invasiveness and comparative life-history traits of exotic and indige- nous Senecio species in Australia. Oecologia 125: 531-542. Randell, R. 2000. Hybridization between naturalized and Endemic Rubus (Rosaceae) Species in Hawai'i. Master’s Thesis. University of Hawaii Department of Botany, Honolulu. Rejmanek, M. 1996. A theory of seed plant invasive- ness: the first sketch. Biological Conservation 78: 171-181. Rejmanek, M. 1999. Invasive plant species and invasi- 32 Newsletter of the Hawaiian Botanical Society ble ecosystems. Pp. 79-102 in O.T. Sandlund, P.J. Schei and A. Vilken (eds.). Invasive species and bio- diversity management. Kluvver Academic Publishers, Dordrecht, Netherlands. Richardson, D.M., I.A.W. Macdonald and G.G. Forsyth. 1989. Reductions in plant species richness under stands of alien trees and shrubs in the fynbos biome. South African Journal of Forestry 149: 1-8. Sun, M. 1997. Population genetic structure of yellow starthistle {Centaurea solstitialis), a colonizing weed in the western United States. Canadian Journal of Botany 7 5: 1470-1478. Thebaud, C. and D. Simberloff. 2001. Are plants really larger in their introduced ranges? American Natural- ist 157(2): 231-236. Thompson, J.D. 1991. The biology of an invasive plant. BioScience 4 1 : 393-40 1 . van Wilgen, B.W., W.J. Bonds, and D.M. Richardson. 1992. Ecosystem management. Pp. 345-371 in R.M. Cowling, editor. The ecology of the Fynbos. Oxford University Press, Cape Town. van Wilgen, B.W., R.M. Cowling, and C.J. Burgers. 1996. Valuation of ecosystem services: a case study from South African Fynbos ecosystems. BioScience 46(3): 184-189. Vitousek, P.M. and Walker, L.R. 1989. Biological inva- sions by Myrica faya in Hawaii: Plant demography, nitrogen fixation, ecosystem effects. Ecological Monographs (59): 257-265. Wagner, W.L., D.R. Herbst, and S.H. Sohmer. 1990. Manual of the flowering plants of the Hawaii. Uni- versity of Hawaii and Bishop Museum Press, Hono- lulu. Walker, L.R. and P.M. Vitousek. 1991. An invader alters germination and growth of a native dominant tree in Hawaii. Ecology 72: 1449-1455. Warwick, S.I., H.J. Beckie, and E. Small. 1999. Trans- genic crops: new weed problems for Canada? Phyto- protection 80(2): 71-84. Weber, E. and C.M. D’ Antonio. 1999. Phenotypic plas- ticity in hybridizing Carpobrotus spp. (Aizoaceae) from coastal California and its role in plant invasion. Canadian Journal of Botany 77: 1411-1418. Williams, D.G., R.N. Mack, and R.A. Black. 1995. Eco- physiology of introduced Pennisetum setaceum on Hawaii: the role of phenotypic plasticity. Ecology 76: 1569-1580. Williams, P.A., E. Nicol, and M. Newfield. 2000. As- sessing the risk to indigenous New Zealand biota from new exotic plant taxa and genetic material. Sci- ence for Conservation 143, Department of Conserva- tion, Wellington, New Zealand. Williamson, M. 1996. Biological invasions. Chapman and Hall, London. Williamson, M.H. and A. Fitter. 1996. The characters of successful invaders. Biological Conservation 78: 163-170. Willis, A.J., M B. Thomas, and J.H. Lawton. 1999. Is the increased vigor of invasive weeds explained by a trade-off between growth and herbivore resistance? Oecologia 120: 632-640. Willis, A.J., J. Memmott, and R.l. Forrester. 2000. Is there evidence for the post-invasion evolution of in- creased size among invasive plant species? Ecology Letters 3: 275-283. Young, J.P. W. and A.W.B. Johnston. 1989. The evolu- tion of specificity in the legume-rhizobium symbio- sis. Trends in Ecology and Evolution 4: 341-349. Volume 40(4), 2001 33 Association of Armillaria mellea with Mamane Decline at Pu6u La‘au Donald E. Gardner USGS-Biological Resources Discipline, Pacific Island Ecosystems Research Center, Department of Botany, University of Hawai‘i at Manoa, Honolulu 96822 Eduardo E. Trujillo Professor Emeritus, Department of Plant and Environmental Protection Sciences, University of Hawai‘i at Manoa, Honolulu 96822 Mamane ( Sophora chrysophylla ) occurs in almost pure stands on the eastern, northern, and western slopes of Mauna Kea (Scott et ah, 1984), and is abundant on the southern slopes (Banko et ah, in press). Over the course of the 1900s, however, these stands have suffered depri- vation from the introduction of alien species such as feral sheep, goats, mouflon sheep, and several species of alien weeds. In addition to habitat competition from the weeds, grasses (the nonnative grasses in particular) in- crease the wildfire danger to unnatural levels, posing a direct threat to mamane forests (Scowcroft and Conrad, 1992). The endangered palila ( Loxioides bailleu), once more widely ranging but now known only from the up- per slopes of Mauna Kea, depends for its subsistence chiefly on immature mamane seeds (Scott et ah, 1984) that it expertly gleans from green seedpods. Thus, threats to the well being of mamane constitute in turn threats to the survival of palila. However, resource man- agers and scientists involved with the recovery of palila populations are currently concerned with an additional, heretofore relatively little understood, threat. Avian scientists who frequent the subalpine dry mamane forest at 6,500-9,500 ft. on the western slope of Mauna Kea near Pu‘u La‘au (see Juvik et ah, 1993) have been aware of its progressive deterioration for a number of years. This site is characterized by an almost pure, but open, scattered stand of mamane with tree height less than 26 ft. (8 m). Because of the lack of recognizable disease signs, such as conks on the trunks, only in recent years has the problem come to the attention of plant pa- thologists. Rather than old age-related senescence, the de- cline appears in trees that should otherwise be vigorous and healthy. Cursory observation indicates that many, if not most trees at the site show symptoms of decline to some degree, from dead twigs and branches and sparse foliage, death of major trunk branches to death of the en- tire tree. Recently killed trees remain standing, as evi- dence of their premature demise. Other than this, no cause for the decline is apparent to the casual observer. The possible role of drought in contributing to the de- cline was considered. Soils of the Pu‘u La‘au site are poorly developed with low amounts of organic matter and little water-holding capacity. Annual rainfall aver- ages 51 1 mm [20 inches] (Scowcroft and Conrad, 1992; Juvik et a!., 1993). However, the wood under the lower trunk bark of declining trees was found to be surprisingly moist, indicating that water deficiency was probably not a factor. A wood-boring cerambycid beetle grub was found in the lower trunks of some of the declining trees. However, our failure to consistently find the larvae in all unhealthy trees sampled suggested that this beetle larva was not the primary cause of the decline. In cutting away the bark of the lower trunk at ground level, we observed white mycelial fans on the cambium and distinctive dark rhizomorphs on the roots of the fun- gus Armillaria mellea. Armillaria is a serious forest pathogen of worldwide distribution and with a broad host range of over 600 species, causing root rot in both coniferous and hardwood trees (Raabe, 1962, 1966). Raabe (1966) reported: “In Hawai‘i, the fungus has been found attacking koa ( Acacia koa ) on the islands of Kaua‘i and Maui, and at Volcano, Kukaiau, and Honau- nau on the island of Hawai‘i. In addition, in the Volcano area, it was found on ‘ohi‘a ( Metrosideros polymorpha ) and in an area above Volcano, it was found killing young plants of Pinus montezumae, P. echinata, P. pinaster , and P. halepens, where these plants were set out on land previously cleared of koa.” The occurrence of Armil- laria on both native hosts (koa and ‘ohi‘a) and nonnative pines should be noted. Bega (1979), listed A. mellea among a number of “higher” heart and root rotting fungi on several thousand acres of deteriorating koa stands on heavily grazed rangeland in the Keanakolu, Halepiula, 34 Newsletter of the Hawaiian Botanical Society and Spring Water Camp areas at an elevation of 5,000 to 6,000 ft. on the northeast side of Mauna Kea. At this site, Armillaria caused a stringy white root and butt rot, producing the characteristic black rhizomorphs (string- like structures comprised of fungal strands) and white mycelial fans by which the fungus could be identified and distinguished from the other fungi present. These other fungi included Phaeolus schweinitzii ( =Polyporus schweinitzii), Polyporus sulphureus, Pleurotus ostreatus, and Ganoderma sp. These fungi readily produce promi- nent, shelf-like conks (fruiting bodies) on the trunks of infected trees, which are the only means whereby the re- spective fungi can be identified in the field. In contrast to the production of conks, at infection sites in most regions other than Hawai'i, A. mellea produces clusters of honey-colored fruiting structures (sporophores or mushrooms) from the base of infected trees. In regions where the fruiting structures are com- mon, their color has given A. mellea the common name “honey fungus.” However, sporophores have not been found in Hawai‘i for an unknown reason (Bega, 1979). Raabe and Trujillo (1963) reported A. mellea from a Christmas tree planting at about 6,000 ft. elevation on the slopes of Mauna Loa, Hawai‘i Island. The fungus was found infecting, and apparently killing, 2-4 year-old saplings of several species of pine that had been set out following the clearing of the land of koa 2 years previ- ously. In a nearby area at about 4,500 ft., a single root of a large, uprooted koa tree was also infected by A. mellea. Armillaria typically enters its host from the soil through the roots and moves between the bark and the xylem tissue (i.e., the hardwood). The fungus encom- passes the root and girdles it, and may also move into and girdle the lower part of the main stem, effectively killing the tree. In Hawai‘i, as mentioned above, Armil- laria root rot produces no definite external symptoms whereby these diseases can be diagnosed. In fact, the lack of such symptoms and signs serves to distinguish it from diseases caused by other wood rotting fungi that produce conks, as noted above. Plants infected with A. mellea may appear unhealthy, have yellow leaves, sparse foliage, and have dead branches. Once infected, trees may live for an extended period while slowly declining, or they may be killed rapidly (Raabe, 1966). Although Armillaria root rot has been reported from some tropical countries, the disease is more common in temperate cli- mates. Where it occurs in the tropics, it is usually found at upper elevations where cooler conditions prevail. In Hawai‘i, the disease has been reported on the islands of Kaua‘i and Maui, and is known from several different locations on the island of Hawai‘i, all at elevations of 3,000 ft. or above (Raabe, 1962, 1966; Raabe and Trujillo, 1963). In a 1974 compilation of the known hosts of A. mellea in the islands, Laemmlen and Bega (1974) listed 23 spe- cies, including mamane, among 1 1 other woody native Hawaiian species. Thus, whereas we have not directly demonstrated the pathogenicity of the fungus recovered from diseased mamane trees at the Pu‘u La‘au site, con- sideration of the above observations leaves little doubt that Armillaria root rot is the cause of the dieback. At present there is no known effective control of Ar- millaria root rot, particularly where it occurs in natural stands of native forest, such as the Pu‘u La‘au forest. Control measures among commercial timber stands or tree crops usually emphasize the use of resistant plants. Literature Cited Banko, P. C., L. Johnson, G. D. Lindsey, S. G. Fancy, T. K. Pratt, J. D. Jacobi, and W. E. Banko. Palila ( Loxioides bailleui). The birds of North America (A. Poole and F. Gill, eds.). The Birds of North Amer- ica, Inc. Philadelphia, PA. In Press. Bega, R V. 1979. Heart and root rot fungi associated with deterioration of Acacia koa on the island of Ha- waii. Plant Disease Reporter 63: 682-684. Juvik, J. O., D. Nullet, P. Banko, K. Hughes. 1993. For- est climatology near the tree line in Hawai‘i. Agri- cultural and Forest Meteorology 66: 159-172. Laemmlen, F., and R. V. Bega. 1974. Hosts of Armil- laria mellea in Hawaii. Plant Disease Reporter 58: 102-103. Raabe, R. D. 1962. Host list of the root rot fungus, Ar- millaria mellea. Hilgardia 33: 25-88. Raabe, R. D. 1966. Armillaria root rot in Hawaii. Ha- waii Farm Science 15: 7-8. Raabe, R. D., and E. E. Trujillo. 1963. Armillaria mellea in Hawaii. Plant Disease Reporter 47: 776. Scott, J. M., S. Mountainspring, C. Van Riper III, C. B. Kepler, J. D. Jacobi, T. A. Burr, and J. G. Giffin. 1984. Annual variation in the distribution, abun- dance, and habitat response of the palila ( Loxioides bailleui). Auk 101: 647-664. Scowcroft, P. G., and C. E. Conrad. 1992. Alien and native plant response to release from feral sheep browsing on Mauna Kea. Pp. 625-665 in: C. P. Stone, C. W. Smith, and J. T. Tunison, (eds.). Alien plant invasions in native ecosystems of Hawai‘i: Management and research. University of Hawai'i Press, Honolulu. Volume 40(4), 2001 35 Hybridization and the Potential Consequences for Rare Plant Species Karen Brimacombe Department of Botany, University of Hawai‘i at Manoa, Honolulu, HI 96822 The phrase “conservation of biodiversity” is being heard around the world. Rates of extinction have climbed to a new high - instigating a rally of efforts based around conservation of rare species. The in- creased rate of species extinctions is mainly due to an- thropogenic actions including habitat fragmentation and destruction (Wilson, 1988). Introduction of exotic spe- cies is another anthropogenic action threatening native species and habitats around the globe. Environmental change, loss of habitat, competition with invasive spe- cies, demographic stochasticity as well as inbreeding de- pression and low genetic diversity are often analyzed and viewed as key reasons for extinction of rare species. Lit- tle research, however, has examined the threat to rare, native plant species resulting from hybridization with introduced taxa. If conservation is the goal, then it is important to accu- rately determine the key threats to rare and native species existence. Hybridization may be one of these key fac- tors, especially given the magnitude of habitat modifica- tion and non-native species introductions in recent years. These actions often bring previously isolated plant taxa into direct contact, which greatly increases the likelihood of hybridization. Hybridization may promote extinction of a rare plant species by reducing the ability of indi- viduals in these populations to replace themselves thereby inhibiting the growth of the population (Levin et al., 1996). With continued hybridization and introgres- sion, the rare species may even be genetically assimi- lated by the more abundant congener and, thus, “lost” as a distinct and unique species (Allendorf et al., 200 1 ). Hybridization Hybridization has been defined as “interbreeding of individuals from what are believed to be genetically dis- tinct populations, regardless of the taxonomic status of such populations” (Rhymer and Simberloff, 1996). Most commonly, hybridization refers to mating among differ- ent species. Evolutionarily, hybridization can result in rapid change by producing novel gene combinations that may lead to increased genetic variation, increased fit- ness, and adaptation to new environments in existing taxa (Rhymer and Simberloff, 1996). Natural hybridiza- tion has most likely played an important role in plant evolution and speciation (Ellstrand et al., 1999). Historically, interspecific hybridization in the wild was believed to be a rare or novel phenomenon (Anderson, 1948). Although, geographic isolation of related taxa was believed to limit the occurrence and impacts of hy- bridization, it was also commonly believed that inter- specific hybrids were sterile (Zirkle, 1935 as stated in Anderson, 1948). Thus, even if hybridization did occur, the hybrids would not persist. It is currently understood that hybridization among related species can often result in fertile or seini-fertile individuals and that hybridiza- tion in the wild has played a role in speciation events. Anthropogenic Affects Anthropogenic actions may be greatly increasing the rate of interspecific hybridization. Currently, introduced plant taxa are commonly brought into contact with rare and native species through human action such as intro- duction of nurse stocks and garden cultivars, creation of disturbed habitat corridors via road building, cultivation of land for agricultural purposes, and accidental intro- duction (Levin, 1996; Freas and Murphy, 1988). In fact, there are many examples of introduced weeds hybridiz- ing with native species. In Hawaii, the introduced Ru- bus rosifolius hybridizes with the endemic R hawaiensis (Randell 2000) and Gossypium barbadense hybridized with the endemic G. tomentosum. In Florida, the tetraploid Lantana camara, an escaped ornamental, has hybridized extensively with the endemic diploid L. de- pressa. The triploid hybrids are quite vigorous and yet manage to retain the local adaptations of the native spe- cies (Sanders,, 1987 as quoted in Levin et al.„ 1996). Further, many endangered sunflower ( Helianthus ) spe- 36 Newsletter of the Hawaiian Botanical Society cies are threatened by hybridization with the weedy H. annuus that has spread widely due to human sowing and disturbance (Rogers et al., 1982 as cited in Rhymer and Simberloff, 1996). Hybridization rates may be heightened when species that are brought together by human action have not evolved reproductive barriers against hybridization. Re- productive barriers may evolve in sympatric populations of closely related species during the natural process of speciation (Raven, 1980). These barriers are one factor that helps maintain species identities. However, repro- ductive barriers would not necessarily by selected for, or evolve in, allopatric and insular populations. Species on islands appear to be particularly vulnerable to hybridization due to their small numbers and the ease with which they interbreed (Levin et al., 1996). Island species tend to be reproductively isolated by habitat rather than by genetic or chromosomal barriers (Rhymer and Simberloff, 1996). In other words, insular species tend to be less genetically divergent and have weaker crossing barriers that make them more prone to inter- breeding (Crawford et al., 1987 as cited in Levin et al.„ 1996). In fact surveys by Rieseberg and Gerber (1995) of the hybrid flora of Hawaii revealed the occurrence of hybridization in close to 40 genera and 23 plant families. The majority of these hybrid combinations involved en- demic, and often rare species of Cyrtandra (67 hybrid combinations), Dubautia (24) Bidens (10 and Clermontia (8) (Rieseberg and Gerber, 1995). Increasing human dis- turbance and introduction of related species to islands amplifies the risk of interspecific hybridization between native and introduced species. Introgression Often hybridization is coupled with introgression. The term introgressive hybridization was coined in the, 1940’s by Edgar Anderson to describe the phenomenon in which hybrid offspring tend to “backcross” or breed with one or both of the parental species (Anderson, 1948). Introgression results in gene flow and mixing of gene pools between previously separated species. Mix- ing of gene pools, particularly in reference to hybridiza- tion between introduced and native taxa, has been given many names including: “contamination,’ ‘ infection, “genetic deterioration,” “genetic swamping and “genetic pollution” (Rhymer and Simberloff, 1996). In- trogression often occurs unequally and it has been dem- onstrated that hybrids tend to backcross preferentially with the more abundant parental species (Potts, 1986; Rieseberg et al., 1996; Caraway et al., 2001). A well-known case of hybridization with introgression in Hawai‘i between an introduced and native species is the case of the mallard duck ( Anas platyrhynchos). The mallard duck has been introduced to many areas around the world including Hawaii. In Hawai‘i, there has been extensive hybridization and introgression among intro- duced mallards and the endangered, endemic koloa (or Hawaian duck; A. wyvilliana). In fact, due to continued hybridization and introgression, it is feared that no “pure” koloa remain on the island of 0‘ahu (Michael Sil- bernagle, personal communication). Generations of hybridization and backcrossing can erode the genetic integrity of a rare species (Levin et al., 1 996). In fact, continued introgression may result in “genetic assimilation” or the incorporation of genes of one species into the gene pool of another species (Rhymer and Simberloff, 1996; Allendorf et al., 2001). Genetic assimilation may dilute allelic frequencies of a rare plant species eventually leading to deterioration of the genetic integrity of this species. This may cause the loss of genotypes of ecologically specialized plant popu- lations. Small, isolated populations that hybridize with a more abundant species and that produce vigorous, fertile hybrids are most at risk of being genetically assimilated. Studies of Cerocarpus trasskaie (Rieseberg and Gerber, 1995), Argyranthemum coronopifolium (Bramwell, 1990), and Atriple x tularensis (Freas and Murphy, 1988) are examples from plant systems that illustrate that ex- tinction of a rare species (via genetic assimilation) by an introduced species is a real, not just theoretical, threat. Hybrid Fitness As previously stated, it was originally believed that F, hybrid individuals are always sterile (Zirkle, 1935). This would prevent the introduction or introgression of novel genes into gene pools of either parental population. However, it is now acknowledged that hybrids demon- strate a range of fertility from complete sterility to com- plete interfertility (Anderson, 1948; Rieseberg, 1996). F,and later generation hybrids have been noted to dem- onstrate either hybrid vigor (Graham et al., 1995; Miibor- row, 1998) or reduced fitness (Raven,, 1980) as com- pared to the parent species. Hybrid vigor, or heterosis, can be defined as the in- crease in growth, size, fecundity, function, yield, or other characters in hybrids over those of the parents (Allaby, 1998). Several studies have indicated that spontaneous hybridization between crops and related wild species oc- curs readily and results in hybrid plants, that exhibit hy- brid vigor (Arriola and Ellstrand, 1996; O’Brien et al., 1967). Hybrids expressing high fitness parameters are not relegated to agricultural setting. Evidence of hybrid Volume 40(4), 2001 37 fitness in natural populations has been demonstrated in Anigozanthos (Hopper, 1978), Iris (Hodges et al., 1996), and Artemesia (Graham et al., 1995) among others. Millborrow (1998) has proposed a biochemical mecha- nism for the increased size and growth rates of heterozy- gote hybrids as compared to two homozygous parental taxa. The mechanism suggested for this “hybrid vigor” includes a “relaxation” of genetic controls that regulate growth due to heterozygosity. This hypothesis assumes that the functioning of several randomly segregating fac- tors restricts growth. Recombination of different alleles of homozygous parents could potentially result in a com- bination that “relaxes” the tight growth control mecha- nisms. This hypothesis was further proposed to account for homeostasis of hybrids in response to environmental changes. Experimental studies of competitive interference (O’Brien, 1967; Hopper, 1978) demonstrate that hybrids may not only be vigorous in their growth, they may also be effective competitors. In these cases, hybrid individu- als exhibited greater survivorship and biomass as com- pared to one of the parental species. Further, one of the parental species had decreased survivorship and biomass when grown with the hybrids. If a hybrid cross is the result of a native/alien hybridization, and if either the in- troduced taxa or the resultant hybrid plants exhibit stronger competitive ability than the native taxa, the re- sult could be the rapid displacement of the native spe- cies. On the other hand, hybridization and introgression can also result in reduced hybrid fitness and outbreeding de- pression (Rieseberg, 1991; Allendorf et al., 2001). Out- breeding depression is the reduction in fitness of first generation as well as later generation hybrids and back- crossed offspring. Outbreeding depression is usually caused by meiotic abnormalities or disruption of co- adapted gene complexes (Dobzhansky, 1948 as quoted in Rieseberg, 1991). For example, segregation difficulties during meiosis may occur due to differences in diploid number of chromosomes in the parental species (Rhymer and Simberloff, 1996). If the F,or later generation hy- brids are partly sterile or have reduced vigor, then the rare parental species may be endangered by outbreeding depression. Ellstrand (1999) points out that outbreeding depression from detrimental gene flow will reduce the fitness of a locally rare species that is mating with a more abundant congener. The rare species may have reduced fitness due to “spending” vital resources such as pollen and ovules on the production of unfit hybrid individuals at the expense of production of “pure” progeny. As only a small percentage of the pollen produced is required to fertilize ovules, the primary cost of outbreeding depres- sion in plants appears to be reduced seed set by the ma- ternal parent (Reieseberg and Gerber, 1995). Hybrid Zones It is often observed that hybrids tend to occupy, or are restricted to, disturbed areas or areas at the boundary be- tween the two parental habitats (Graham et al., 1995). The term “hybrid zone” is often used to describe this re- gion in which genetically distinct populations meet, mate, and produce hybrids (Barton and Hewitt, 1989). Formation of hybrid zones may result from secondary contact between populations that have differentiated in allopatry (Hodges et al., 1996). Hybrid zones between divergent taxa sometimes remain distinct despite gene exchange at narrow zones of contact (Freeman et al., 1991). Explanation for maintenance of hybrid zones includes the “bounded hybrid superiority” hypothesis. This hy- pothesis proposes that hybrid zones are areas of ecologi- cal transition where hybrids exhibit superior fitness to either parental type (Arnold, 1992). In other words, due to increased genetic variability via recombination, hy- brids are able to occupy niches unfavorable to either par- ent (Anderson, 1948; Hopper, 1978). Thus, within this zone there is no selection against hybrids and conse- quently reproductive isolation does not evolve allowing the zone to persist (Freeman et al., 1991). A second theory for the creation and maintenance of hybrid zones is the “dynamic equilibrium hypothe- sis” (Barton, 1979). The dynamic equilibrium theory is based on the concept of outbreeding depression. This theory assumes that hybrids have lower fitness than ei- ther parent regardless of habitat, and thus are selected against in the parental habitat. This selection against hy- brids restricts them to the zone between the parental habitats. A third model is that of the “tension zone” and is based on the assumption that natural selection acts against hybrids and restricts them to zone of tension be- tween the parental populations (Burke et al., 1998).. Limited gene flow by means of pollen and seed disper- sal has also been cited as causes for creation of hybrid zones. A study of two species of Anigozanthos and their F| hybrids determined that pollen and seed flow limita- tions were the main underlying reason why hybrids are found in confined distributions (Hopper, 1978). However, habitats are often not stable and/or two spe- cies are brought together by human action or distur- bance. Instead of having an intermediate habitat that supports a hybrid zone there may now be a mosaic of fragmented microhabitats and/or the introduction of a superior competitor. Spatial and ecological separation of 38 Newsletter of the Hawaiian Botanical Society two previously isolated species may be completely bro- ken down and may result in production of a hybrid swarm. The term “hybrid swarm” has been used to de- scribe areas in which extensive hybridization and intro- gression among hybrids and between the hybrids and both parental species is occurring. Hybrid plants in these areas may appear intermediate between parental types or exhibit any combination of parental characters. Hybridization and introgression in these swarms may result in fusion of two populations into a single popula- tion that is highly variable and in which “pure” indi- viduals of either species are infrequent or absent. If both species are in small, localized populations and contribute similarly to a hybrid swarm, the genetic in- tegrity of both species may be lost (Levin et al ., 1996). However, if one species is dominant in an area where a hybrid swarm is forming, the minor species often de- clines over time. This process is a threat to the conser- vation of rare species and their unique phenotypes and genotypes. The Demographics of Hybridization Introduction of and subsequent hybridization with non-native species can have dramatic effects not only on the genetic structure of the native species, but also on the population demographics of a native species. Hybridization makes a population vulnerable due to ga- metic wastage, reduced seed set, production of ill-fit progeny and pollen swamping (Levin et al., 1996). In small fragmented populations, lack of plentiful con- specific individuals may increase the chance of inter- specific hybridization, especially if the introduced taxon is more abundant (Byers and Meagher, 1992). Both lack of available mates and available habitat have been described as limiting the population growth and continued survival of rare species (Lande, 1988; Eriks- son and Ehrlen, 1992). Production of hybrid seed and pollen “swamping” of a rare species by an abundant introduced species may result in decreased rates of “pure” progeny. This proc- ess has been examined in a study by Potts (1986) of Eucalyptus risdonii and E. amygdalina. Regeneration of the two species of Eucalyptus and their hybrids was charted after a wildfire. Results showed that a large proportion of F| hybrids were produced from seed of the less abundant species E. amygdalina. It was in- ferred that this was due to fertilization of E. amygdalina individuals by the plentiful pollen of E. risdonii. Thus, the more abundant species was reducing the rate of “pure” progeny of E. amygdalina via pollen swamp- ing.” Rare species cannot afford such “gametic wast- age” (Levin et al., 1996) as survival and integrity of the species may depend on high rates of reproduction. Theoretically, a situation involving a rare native spe- cies and an aggressive and abundant introduced conge- ner could result in the introduced species swamping out the native species via increased pollen flow, higher re- productive fitness, and unequal rates of hybrid seed be- ing produced by each taxon. If these forces are not compensated for by regeneration via immigration of seeds or pollen of the native species, it could have a detrimental effect on survival of the native species. Human impact continues to destroy and fragment vital habitat causing populations of rare species to become excessively small and fragmented. Geographic isola- tion of populations (via habitat fragmentation) hinders regeneration of population size due to a decrease in mi- gration among populations via seed or pollen dispersal (Lande, 1988). As populations of rare species tend to be geographically isolated the effects of increased gene flow and competition from abundant introduced taxa are not likely to be counterbalanced by immigration of the native species. Conclusion In the absence of hybridization, the interaction be- tween a native and introduced species is essentially a competitive one. Hybridization resulting in vigorous hybrids creates a two-fold threat to a rare species. Re- production via hybridization results in loss of “pure” progeny or “gametic wastage.” Concurrently, vigorous hybrids may be able to effectively compete or even out- compete individuals of the native taxon. A study by Huxel (1999) suggested that “in cases where related taxa are able to interbreed, introductions may lead to the introduced taxa dying out, coexistence, new hybrid taxa or extinction of the native taxa.” If the introduced species happens to be a stronger competitor, it can potentially “outcompete” and displace the native taxon. Adding hybridization and introgression to the equation increases the chances of displacement of rare species due to genetic “swamping” and added competi- tion from hybrids. A native species could theoretically be overwhelmed and displaced in a short time period if immigration of the introduced species and the rate of hybridization and introgression are all high and there is low replacement or immigration between populations of the native species (Huxel, 1999). Although few studies have documented the displacement of native species via hybridization, studies by Rieseberg and Gerber (1995), Bramwell (1990), and Freas and Mur- phy (1988) show that it is quite possible. Effective Volume 40(4), 2001 39 conservation strategies not only need to identify the life history stages that appear to restrict a rare species per- sistence and growth, but must also identify all outside threats. These threats include not only habitat destruc- tion and loss, but also the threat of hybridization and introgression with introduced species. Literature Cited Allendorf, F. W., R. F. Leary, P. Spruell, and J. K. Wenburg. 2001. The problems with hybrids: set- ting conservation guidelines. Trends in Ecology and Evolution 16: 613-622. Anderson, E. 1948. Hybridization of the habitat. Evo- lution. 2: 1-9. Allaby, M. 1998. A Dictionary of Plant Sciences. Ox- ford University Press. New York, New York. USA. 508 pp. Arnold, M.L. 1992. Natural hybridization as an evolu- tionary process. Annual Review of Ecology and Systematics 23: 237-261. Arriola, P.E., and N.C. Ellstrand. 1996. Crop-to-weed gene flow in the genus Sorghum (Poaceae): sponta- neous interspecific hybridization between johnson grass, Sorghum jalapense, and crop sorghum, S. bi- color. American Journal of Botany 83 : 1153-1160. Arriola, P.e., and N.C. Ellstrand. 1997. Fitness of in- terspecific hybrids in the genus Sorghum: persis- tence of crop genes in wild populations. Ecological Applications 7: 512-518. Barton, N.H. 1979. The dynamics of hybrid zones. Heredity 43: 341-359. Barton, N.H, and G.M. Hewitt. 1989. Adaptation, speciation and hybrid zones. Nature 34 1 : 497-503. Blossey, B., and R. Notzold. 1995. Evolution of in- creased competitive ability in invasive non- indigenous plants: a hypothesis. Journal of Ecology 83: 887-889. Bramwell, D. 1990. Conserving biodiversity in the Ca- nary Islands. Annals of the Missouri Botanical Gar- den 77:28-37. Burke, J.M., S.E. Carney and M.L. Arnold. 1998. Hy- brid fitness in the Louisiana Irises: analysis of pa- rental and F, performance. Evolution 52(1): 37-43. Byers, D.L., and Meagher, T.R. 1992. Mate availabil- ity in small populations of plant species with homo- morphic sporophytic self-incompatibility. Heredity 88: 353-359. Caraway, V., G. D. Carr, and C. W. Morden. 2001. Assessment of hybridization and introgression in lava-colonizing Hawaiian Dubautia (Asteraceae: Madiinae) using RAPD markers. American Journal of Botany 88: 1688-1294. Crawford, D.J., R. Witkus, and T.F. Stuessy. 1987. Plant evolution and speciation on oceanic islands, pp 183- 199. In K.M. Underwood (ed.) Differentia- tion Patterns in Higher Plants. Academy Press. London. Eriksson, O., and J. Ehrlen. 1992. Seed and microsite limitation of recruitment in plant populations. Oecologia91: 360-364. Ellstrand, N.C., H.C. Prentice and J.F. Hancock. 1999. Gene flow and introgression from domesticated plants into their wild relatives. Annual Review of Ecology and Systematics 30: 539-563. Freas, K.E., and D.D. Murphy. 1988. Taxonomy and the conservation of the critically endangered Ba- kersfield saltbush, Atriplex tularensis. Biological Conservation 46:317-324. Freeman, D.C., W.A. Turner, E.D. McArthur and J.H. Graham. 1991. Characterization of a narrow hy- brid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). American Jour- nal of Botany 78: 805-815. Graham, J.H, D.C. Freeman and E.D. McArthur. 1995. Narrow hybrid zone between two subspecies of big sagebrush (Artemisia tridentata: Asteraceae). II. Selection gradients and hybrid fitness. American Journal of Botany 82: 709-716. Hodges, S. A., J.M. Burke and M.L. Arnold. 1996. Natural formationof Iris hybrids: experimental evi- dence on the establishment of hybrid zones. Evolu- tion 50: 2504-2509. Hopper, S.D. 1978. An experimental study of competi- tive interference between Angozanthos manglesii D. Don, A. humilis Lindl. and their F, hybrids (Haemodoraceae). Australian Journal of Botany 26: 807-817. Huxel, G.R. 1999. Rapid displacement of native spe- cies by invasive species: effects of hybridization. Biological Conservation 89: 143-152. Lande, R. 1988. Genetics and demography in biologi- cal conservation. Science 241: 1455-1460. Levin, D.A., J. Francisco-Ortega and R.K. Jansen. 1996. Hybridization and the extinction of rare plant species. Conservation Biology 10: 10-16. Millborrow, B.V. 1998. A biochemical mechanism for hybrid vigor. Journal of Experimental Botany 49: 1063-1071. O’Brien, T.A., W.K. Whittington and P. Slack. 1967. Competition between perennial ryegrass, meadow fescue and their natural hybrid: variation in growth rates and in the proportion of each species with 40 Newsletter of the Hawaiian Botanical Society time. Journal of Applied Ecology 4: 501-512. Potts, B.M. 1986. Population dynamics and regenera- tion of a hybrid zone between Eucalyptus risdonii Hook.f. and E. amygdalina Labi 1 1 . Australian Journal of Botany 34: 305-329. Randell, R. 2000. Hybridization between naturalized and Endemic Rubus (Rosaceae) Species in Hawai‘i. Master’s Thesis. University of Hawaii Department of Botany, Honolulu. Raven, P.H. 1980. Hybridization and the nature of species in higher plants. Canadian Botanical Asso- ciation Bulletin 13: 3-10 (Supplement). Rhymer, J.M., and D. Simberloff. 1996. Extinction by hybridization and introgression. Annual Review of Ecology and Systematics 27: 83-109. Rieseberg, L.H. 1991. Hybridization in rare plants: insights from case studies in Cercocarpus and Heli- anthus. In D.A. Falk (ed.) Genetics and Conserva- tion of Rare Plants. Oxford University Press, New York, USA. Rieseberg, L.H., and D. Gerber. 1995. Hybridization in the Catalina Island mountain mahogany ( Cercocarpus traskiae): RAPD evidence. Conser- vation Biology 9: 199-203. Reiseberg, L.H., B. Sinervo, C.R. Linder, M.C.Ungerer and D.M. Arias. 1996. Role of gene interactions in hybrid speciation evidence from ancient and experi- mental hybrids. Science 272: 741-745. Rogers, C.E., T.E. Thompson and G.J. Seiler. 1982. Sunflower Species of the United States. National Sunflower Association. Bismarck, N.D. Sanders, R.W. 1987. Identity of Lantana depressa and L. ovatifolia (Verbenaceae) of Florida and the Ba- hamas. Systematic Botany 12: 44-60. Wilson, E.O. 1988. Biodiversity. National Academy Press. Washington D.C. MINUTES OF THE HAWAIIAN BOTANICAL SOCIETY October 1, 2001 Guests: Rene Johanssen, Molokai resident, Cheryl Sea- man Minutes: Approved as read. Treasurer's Report: Treasurer’s report given for the months of June to August June, start: $2182.93 Income: dues: $197 (and change) Posters: $21 B.Krauss: $72.08 Life Member Fund: $22.40 Interest: $29.50 Outgo: postage: $82.00 Copies: $44.58 Refreshments: $34.46 Stationary: $29.1 1 September, end: $2853.68 (I know it probably doesn’t balance out, as I think I missed a few numbers). Announcements: • Alvin Yoshinaga gave away Delissea rhyti- dosperma seedlings from Keith Robinson’s preserve on Kaua‘i. • Betsy Gagne announced an alien plant control ser- vice trip to Manuka NAR on the Big Island over Veteran’s Day weekend (Nov 10-12); contact Betsy for more details. • T-shirts, mugs and tote bags from the 2001 SCB/ Hawaii Conservation Conference are STILL avail- able from the PCSU office in St. John 409 or from Chuck Chimera (chimera@hawaii.edu). Old Business: • Nominating committee is still looking for new board members. New Business: • None Plant of the Month and Speaker: • Web Site of the Month: Hawaiian Native Plant Propagation (www.ctahr.hawaii.edu:591/hawnprop/, Eileen Herring. Topic and Speaker: • Palms- The Tree of Life, Melany Chapin, Na- tional Tropical Botanical Garden. Volume 40(4), 2001 41 November 5, 2001 Guests: Sheila Foreman, Kanoa Kimble Minutes: Approved as read. Treasurer's Report: Start: $2853.68 Expenses: $323 (mostly newsletter expenses) Income: $80.3 1 End:$26 10.99 Announcements: • Carol Annable announced that Waimea Arboretum is having a Christmas plant sale on December 8th. • Betsy Gagne announced that there were still a few openings for an alien plant control service trip to Manuka NAR on the Big Island over Veteran’s Day weekend (Nov 10-12); contact Betsy for more de- tails. • Ray Baker announced that the Volunteer Steward- ship Network would be rescheduling its service trip leader training for the beginning of 2002; more to follow. • Ray Baker also announced that Lyon Arboretum would be having a plant sale on November 17th from 9:00 a.m.-2:00 p.m. • T-shirts, mugs and tote bags from the 2001 SCB/ Hawaii Conservation Conference are STILL YET available from the PCSU office in St. John 409 or from Chuck Chimera (chimera@hawaii.edu). Old Business: • Vickie Caraway announced the nominees for the 2002 Hawaiian Botanical Society board as follows: President: Susan Harbin Vice President: Joan Canfield Secretary: Chuck Chimera Treasurer: Ron Fenstemacher Board: Jeff Preble and Brandon Stone Nominations are still being accepted. Please contact Vickie Caraway if you or anyone you know may be in- terested. New Business: • Vickie Caraway reported that the Board of Land and Natural Resources would be holding a public meeting on Friday, November 16th in Kona to dis- cuss the future of the lease of Pu'u wa'awa, one of the last and nicest patches of dryland forest left in the state. Possibilities include a return to ranching, greater access to hunting, or protection and conser- vation. Vickie motioned that Bot Soc send a repre- sentative (Betsy Gagne on vacation) to testify on behalf of the conservation of the area. The motion was seconded and passed unanimously. Good luck! Plant of the Month: Nuts about Nutmeg and Mad about Mace: The Ethnobotany of Myristica fragrans by Jodi Stevens, UH Botany De- partment. Topic/Speaker: Mexican Mariachi, Big Bromeliads & Panamanian Peccaries: Links Between Culture & Con- servation in a Neotropical Rainforest by Dr. Tamara Ticktin, UH Botany Department. December 3, 2001 Guests: Jean Larr Minutes: Approved as read. Treasurer's Report: Start: $2610.99 Expenses: $160.29 Income: $53.86 End:$2504.56 Announcements: • Betsy Gagne announced that she had free watershed posters for distribution. • Carol Annable announced a plant sale at Waimea Arboretum on December 8th. • Betsy Gagne announced that there has been no de- cision made on the status of Pu'uwa awa a, but that 59 people signed up to testify on behalf of conser- vation. • Betsy Gagne also announced that the Honolulu Academy of Arts was displaying “Remains of A Rainbow” throughout the month of December. • Chuck Chimera announced the publication of a new newsletter. • T-shirts, mugs and tote bags from the 2001 SCB/ Hawaii Conservation Conference are STILL YET available from the PCSU office in St. John 409 or from Chuck Chimera (chimera@hawaii.edu). 42 Newsletter of the Hawaiian Botanical Society Old Business: • Carol Annable informed the society that we had 64 renewals as a result of the membership drive, and got several new members as well. New Business: • The “election” results for the 2002 Hawaiian Botanical Society executive committee are as follows: President: Susan Harbin (hail to the chief!) Vice President: Joan Canfield (welcome aboard Joan) Secretary: Chuck Chimera (t-shirts any- one?) Treasurer: Ron Fenstemacher (mahalo for taking the job nobody wants) Board: Jeff Preble and Brandon Stone (ready to step in and fill any of the above positions, especially secretary, at a moment’s notice). • Mahalo nui loa to Dr. Don Gardner, outgoing Vice President, for the outstanding job he did throughout 2001 with both the selection of speakers AND the publication of the newsletter. Don will be sorely missed. Plant of the Month: Kahili Ginger: Battling the fra- grant invader, Rob Anderson, USGS-Biological Re- sources Division. Topic/Speaker: Pu'u Kukui Watershed: The Bleeding Edge of Resource Management, Randy Bartlett, Maui Land and Pineapple. treasurer s report JANUARY TO DECEMBER 2000 The Hawaiian Botanical Society had an unusual financial year Annual dues income was way off but as no Newsletters were issued, it’s a draw The Life Member Fund finished about $5.00 short of Its ultimate financial goal, so by early next year it starts leaving block ink on the Annual Fund's bottom line. Awhile ago, longtime member Bea Krauss kindly remembered the Society in her will Her legacy was realized this year and went to the Neal-Miller-Krauss Fund The treasurer would like to thank Jonel L. Smith for her thorough financial audit of the Society's books for 1999 Finally it is with great sorrow to note the sudden passing of two distinguished and longtime life members, William Hoe and Cliarles Lamoureux, While the Society can say or do little to beguile friends and loved ones from such overwhelming loss, all our hearts hold profound sympathy for each cir\(i every one weathering difficult times 2000 Annual Fund Summary Income Outgo Annual C)UM $315 OO ^ Annual Payment $250 OO Donation $200 OO Science Fair $248 32 Plantasia $60,00 Postage $235 OO 75**’ Anniversary $39 55 Memonam $100 00 Interest $38.93 Copying $95 27 Total $653 48 Stationery $22 49 Refreshments $20.01 T otal $971.09 Volume 40(4), 2001 43 Beginning Bo lance ♦ Income - Outgo = Ending Balance $3116 00 ♦ $653 48 - $971.09 = $2800 39 The net loss for the Annual Fund in 2000 is $317.61. 2000 Annual Dues Summary: Student. 3 x 1 yr $1500 Individual, 16 x 1 yr $160.00 2 x 2 yr $40.00 Family, 5 x 1 yr $60 00 Institutional 1 x 1 yr $20 00 Cash $2900 Total $31500 Life Member Fund Summary: Income Interest $367 20 99 Life Dues (2) $36000 00 Life Dues (2) $36000 f Annual Payment $250.00 Donation $150.00 Total $1487.20 Outgo none Beginning Balance ♦ Income - Outgo = Ending Balance $5768.68 ♦ $1487.20 - $0.00 = $7255.88 The LMF began 2000 with a target sum of $7020.00. The Society gained three life members during the year (3 x $180.00 = $540.00) but lost two (2 x $150 00 = $300.00), resetting the yearend LMF target sum to $7260.00. The difference between this target sum and the yearend balance is $4 12 One life membership was realized too late to augment the LMF within the year and will join the account at its next maturity date in January 2001 These pending dues along with whatever interest the account realizes exceed $4 12. In other words, the LMF achieves its financial goal and is fully funded in January 2001, finally to generate income for the Annual Fund Respectfully Submitted, R. Fenstemacher. Treasurer o K* fij £?:•- “T* M* O di 1*# o 03 3 c 3 CL (Q CD ro ro O < 3’ r— ♦* >c > < CD O ro co 00 0 3 < 1 CD —1 O’ 03 c‘ 3 cr 3 I CD —5 < 0) - s Q. C 3 c » CE 3 s “ > <0 ■< 0) 00 10 ro m ° w 3 rn r 5 5m *2 > H 3 ■ -< H m 0 g » T1 5 0 1 5 : 1 2 1 5 11 m - 08 I > H | H > w -■ Z > S*1 o 03 > o H *> O > (/> o o m