Life Sciences Contributions
Royal Ontario Museum 1 1 T

Distribution and Call Parameters

of Hyla chrysoscelis and
FAlyla versicolor in Michigan

James P. Bogart
Alan P. Jaslow

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LIFE SCIENCES CONTRIBUTIONS
ROYAL ONTARIO MUSEUM
NUMBER 117

oe |. istmoution, ang Call Parameters
ALAN P. JASLOW

of Hyla chrysoscelis and

Ayla versicolor in Michigan

ROM

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JAMES P. BOGART is a Research Associate in the Department of Ichthyology and Herpetology, Royal Ontario
Museum, and a member of the Department of Zoology at the University of Guelph, Guelph, Ontario.

ALAN P. JASLOW is a graduate student in the Museum of Zoology, University of Michigan, Ann Arbor and is
now at the Smithsonian Tropical Research Unit, Balboa, Canal Zone.

Canadian Cataloguing in Publication Data

Bogart, James P.
Distribution and call parameters of Hyla
chrysoscelis and Hyla versicolor in Michigan

(Life sciences contributions; no. 117
ISSN 0384-8159)

Bibliography: p.
ISBN 0-88854-229-1 pa.

1. Hylidae. 2. Frogs — Michigan. 3. Amphibians —
Michigan. I. Jaslow, Alan P. II. Royal Ontario
Museum. III. Title. IV. Series.

QL668.E24B64 597.8'09774 C79-094314-X

Publication date: 1 June 1979
©The Royal Ontario Museum, 1979
100 Queen’s Park, Toronto, Canada MSS 2C6

PRINTED IN CANADA AT THE ALGER PRESS

Distribution and Call Parameters
of Hyla chrysoscelis and Hyla versicolor
in Michigan

Abstract

Information from chromosomes, nucleolar determinations from
preserved specimens, and mating call analyses revealed the presence
of Hyla chrysoscelis populations in seven Michigan counties. Call
analyses indicate that Michigan H. chrysoscelis are more similar to
Wisconsin and ‘‘western’’ populations than to ‘‘eastern’’ populations
of H. chrysoscelis. Most Michigan H. chrysoscelis occur sympatri-
cally with H. versicolor which is widespread throughout the state.

Introduction

The present distribution of Hyla chrysoscelis and its morphological, tetraploid
counterpart, H. versicolor has been estimated from pulse rate analyses of calling
males involving relatively few populations (Blair, 1958; Johnson, 1966; Ralin, 1968,
1977; Zweifel, 1970; Gerhardt, 1974; Jaslow and Vogt, 1977).

Identification, and therefore determination of distribution, is complicated by the
fact that pulse rate is temperature dependent. In some populations, a ‘‘hot’’ H.
versicolor male recorded on a warm night might be confused with a ‘‘cold’’ H.
chrysoscelis male recorded on a cool night (Zweifel, 1970; Gerhardt, 1978). Call
differences may easily be perceived by ear without bioacoustic analysis if the species
occur in sympatry and are both calling together at similar temperatures. The two call
types were heard on June 14, 1974 during an overnight stay in Portage Lake State
Park Campground, Jackson County, Michigan. Tape recordings were not obtained at
that time but voucher specimens of each call type were captured and karyotyped.
From the chromosomal information, it was evident that H. chrysoscelis occurs
sympatrically with H. versicolor at that locality.

Finding H. chrysoscelis in Michigan was unexpected in that the closest published
record of H. chrysoscelis to the west is northern Illinois (Brown and Brown, 1972)
and the tentative map provided by Ralin (1968) indicated that H. chrysoscelis should
not occur north of central Ohio and Indiana. Blair (1958), and more recently Gerhardt
(1974, 1978), Maxson et al. (1977), and Ralin (1977) discuss a possible partitioning
of H. chrysoscelis. This study was undertaken to determine the distribution and
possible interpopulational affinities of the Michigan treefrogs.

Materials and Methods

Trips were made through some of the southern counties of Michigan from May
through July, 1975. Calls were recorded using a Uher 4000S recorder at a tape speed
of 19 cm/sec and a Uher M517 microphone. The tapes were analysed with a Kay
Electric Sound Spectrograph (7030A) using an effective band width filter of 300 Hz
at 1/2 playback speed for pulse rate analysis. Sections were run from calls played
back at normal speed using the narrow band width filter (45 Hz) for frequency
determinations. Call duration was determined by measuring sonograms using the
middle three calls for each individual.

Esophageal temperatures of recorded individuals were taken using a Schultheis
thermometer except for two H. versicolor males which were calling from the water,
in which case the temperature of the water was used for regression analyses. Ten H.
chrysoscelis males were recorded from five localities and nine H. versicolor males
were recorded from five localities. Least squares regression analyses were used to
calculate the regression of pulse repetition rate vs temperature, call duration vs
temperature, and dominant frequency vs temperature.

Chromosomes were obtained from three H. chrysoscelis males and from six H.
versicolor males at one sympatric locality (Portage Lake State Park). The methods
used for obtaining chromosomes were the same as in Bogart (1968). Preserved
specimens were borrowed from the Museum of Zoology at the University of
Michigan and the University of Kansas Museum of Natural History for nucleolar
number determinations using the procedure of Fernandez-Gomez et al. (1969) as
outlined by Cash and Bogart (1978).

Results

The collected specimens of each call type, distinguished by call, at the Portage Lake
State Park all possessed the expected chromosome complement of 48 chromosomes
for H. versicolor and 24 for H. chrysoscelis. The karyotypes are basically similar to
those published by Bogart and Wasserman (1972). The accumulated locality
information for Michigan H. chrysoscelis and H. versicolor is included in Table 1 and
on the map (Fig. 1). Most of the localities for H. versicolor were determined entirely
from nucleolar counts from preserved frogs. These do not represent the entire
preserved collection examined because some of the specimens did not reveal
sufficient cellular detail to determine accurately the number of nucleoli. The
relationship of pulse rate to temperature proved to be the only highly significant
(P<0.005) correlation for calling males of both species (Fig. 2). The regression
formulae for Michigan H. chrysoscelis is: Y = 3.78X — 33.93 (r’ = .81) and for H.
versicolor is. Y = 1.32X — 7.50 (r? = .90). Determinations of call parameters for
both species in Michigan is included in Table 2.

Fig. 1 Distribution, by counties, of Hyla versicolor and H. chrysoscelis in Michigan. Counties where H.
chrysoscelis is sympatric with H. versicolor are indicated by open circles. Closed circles indicate
those counties which have revealed only the presence of H. versicolor.

Table 1 Locality information for Hyla chrysoscelis and H. versicolor in Michigan. UM and KU
numbers refer to catalogued specimens used for nucleolar determinations from the
Museum of Zoology at the University of Michigan (UM) or the University of Kansas
Museum of Natural History (KU).
Locality
County H. versicolor H. chrysoscelis
Alcona: Sprinkler Lake (UM128633)
Allegan: Wayland (UM84198)
Barry: T3N/R9OW/S32*?;, TIN/ROW/S3223; T2N/R8W/S 12; T3N/R8W/S36>
T2N/R8W/S 14; T3N/R8W/S36? T3N/R10W/S294; TIN/R9W/S2?
T2N/R9OW/S22°
Berrien: Harbert (UM51186-7); Warrens Harbert (UM51188); Sawyer
dunes (UM54374) (UM53235)
Calhoun: T2S/R4W2; Marshall (UM83266)
Cheboygan: Douglas Lake (KU55510)
Clare: Budd Lake (UM84726)
Clinton: Rose Lake (UM96164)
Eaton: T2N/R5W/S3?; Olivet (UM90743);
Charlotte (UM83792)
Gratiot: Alma (UM56317) Alma (UM56316)
Huron: Caseville (UM37898; UM37904)
Sand Point (UM37902-3; UM37899)
Ingham: Whiteoak Twp. (UM56633; UM56728;
UMS56732); Leslie (UM83791)
Ionia: Boston Twp. (UM89637)
Jackson: Portage Lake State Parkd; Portage Lake State Parkd;
T3S/R2E/S224, T2S/R2E/S4°; T2S/R2E/S4°; T1S/R2E/S34?
T1S/R2E/S34?; T1S/R2E/S284
Manchester (UM56571); Grass Lake
(UM83793); (UM118458)
Kalkaska: (UM65070); (UM69546) (UM69340)
Kalamazoo: Agusta (UM83813); (UM77598)
Keweenaw: Lake Bailey (UM83777)
Livingston: TIN/R4E4; T1N/R4E/S29*; Brighton T1N/R2E/S34?
(UM30656); Whitmore Lake
(KU68852; KU68855-6)
Marquette: Marquette (UM83890); (UM88440);
Moccasin Lake (UM100193-4)
Mecosta: Paris (UM63136); Remus (UM11712)
Newaygo: (UM63457)
Ogemaw: Sage Lake (UM89648)
Otsego: Pigeon River (UM110529)
Rosscommon: (UM122550)
Sanilac: Melvin (UM96167)
Shiawassee: Hopkins Lake (UM74539)
Van Buren: South Haven (UM103667); Wolf

Lake (UM116309)

Table 1 continued

County Locality
H. versicolor H. chrysoscelis

Washtenaw: T3S/R4E/S23>; T1S/R4E/S4&9*, T1S/R3E/S28°; T2S/R3E/S5?
T2S/R3E/S6*; T2S/R3E/S5?;
T1S/R3E/S284; T1S/R3D/S203;
T2S/RSE*; Ann Arbor (UM30805;
UM30707; UM30654-5; UM99999;
UM99408); Dixboro (KU68845-6;
KU68848)
Wayne: Dearborn (UM51920-1; Denton
(UM31600)

* Township/Range/Section number; 4 Determined by call only; One specimen recorded; °‘ Two
specimens recorded; 4 Three specimens recorded.

Table 2 Call parameters in Michigan Hyla chrysoscelis and Hyla versicolor populations + 95%
confidence limits. Ranges are included in parentheses.

Mean Mean pulse Mean call Mean dominant
Species N temperature repetition rate duration frequency
(C) (pulses/sec) (sec) (KHz)
Hyla chrysoscelis 10 23.2 saz. FO 0.46 + 0.06 2252 = 0:07

(21.0 — 26,0) (40.7 — 67.5) (0.34 — 0:59) 217 — 3.00)

Hyla versicolor 9 22.5 23:3). DY. 0.57 + 0.08 2.29 20.03
(20:2) —526.0) (18.7 =.26.0) (0.34 — 0.73) (2.135) 2.55)

Discussion

Populations of H. chrysoscelis in Michigan appear to be concentrated in the southern
counties and at all the localities but one (south of Cloverdale in Barry county) H.
chrysoscelis occurs sympatrically with H. versicolor. The distribution of H.
chrysoscelis is probably more widespread than indicated here as our sampling was
concentrated, for field collecting and recording specimens, in a few areas in southern
Michigan. The museum specimens were from scattered localities and, in most cases,
the populations were represented by only one or a few individuals. Even if the two
species occurred sympatrically, H. chrysoscelis might not be represented in a small
sample. At the one allopatric locality, only two individuals of H. chrysoscelis were
heard and under more favourable conditions, it is possible that H. versicolor would be
encountered. Since our study concentrated on locating populations of H.
chrysoscelis, many allopatric populations of H. versicolor were not examined in
detail and most of the H. versicolor recorded for this study were, for convenience,
from sympatric localities.

Personal observations from extensive collecting in other localities in various parts
of the range of these two species, reveal the calling male H. chrysoscelis in Michigan
to be similar to those from Wisconsin and different from those of Texas, Louisiana,
and North Carolina. In Michigan, they are smaller and usually all green with few, if
any, dorsal markings. The green colour is brighter and more intense than any of the
green H. versicolor or the more southern H. chrysoscelis in their green colour phase
and extends to the throat where it may appear yellow-green. The colour of Michigan
calling H. chrysoscelis is reminiscent of the colour of the green treefrog, H. cinerea.
Vocalizing H. versicolor in Michigan appear comparatively larger than the Michigan
H. chrysoscelis , have dorsal markings, and are usually moss and kelly-green although
some brown and grey individuals were calling.

The small number of H. chrysoscelis examined in our study does not provide an
adequate sample size to draw any significance from mean snout-vent lengths nor is
the colour difference apparent in preserved specimens. It is interesting to note,
however, that Wisconsin H. chrysoscelis, which appear most similar to Michigan H.
chrysoscelis were found to be smaller (mean size 35.2 mm) (Jaslow and Vogt, 1977)
than H. chrysoscelis in Texas, with a mean size of approximately 40.5 mm
(extrapolated from fig. | in Ralin, 1968). H. versicolor does not seem to possess this
latitudinal difference in size and from these same studies, has a mean size of 42.6 mm
(Wisconsin) and approximately 42.5 mm (Texas).

Gerhardt (1974) found that Georgia and South Carolina populations of H.
chrysoscelis differed from Texas populations in two call parameters; pulse repetition
rate and mean call duration. In Gerhardt’s discrimination experiments, females
preferentially chose males from their own region. Ralin (1977) also indicated that H.
chrysoscelis could be divided, east and west, by pulse rate, call duration, and
electrophoresis. He differentiated two populations of H. versicolor, north and south,
which could be distinguished by call and electrophoresis. Southern populations had a
faster pulse repetition rate. Microcomplement fixation studies by Maxson et al.
(1977) have also indicated separation of H. chrysoscelis into two differentiated
populations. Considering the possible differentiation between the various popula-
tions, it should be instructive to compare the Michigan populations with ‘‘eastern’’
and ‘‘western’’ H. chrysoscelis and ‘‘northern’’ and ‘‘southern’’ H. versicolor.

8

Call Duration

Both Gerhardt (1974) and Ralin (1977) provide evidence that the ‘‘eastern’’ H.
chrysoscelis has a much longer estimated mean call than ‘“‘western’’ H. chrysoscelis.
In our analysis of call duration for Michigan H. chrysoscelis and H. versicolor, we
found that regression equations (call duration vs temperature) were not statistically
valid and correction for temperature was, therefore, not possible over our temperature
range for either species. Our mean call duration (0.46 + 0.06) compares most
favourably with Gerhardt’s value of 0.45 + 0.02 for Texas frogs (opposed to
0.75 + 0.05 for Georgia and South Carolina H. chrysoscelis). Regression equations
for call duration have only been provided by Ralin (1977) for his ‘‘eastern’’
Y = —0.04X + 1.73) and ‘‘western’’ (Y = —0.02X + 1.23) populations of H.
chrysoscelis. Substituting our mean temperature of 23.3 for X in Ralin’s equations,
we obtain a duration of 0.80 (‘‘eastern’’) and 0.76 (‘‘western’’). Neither of these
values would be considered close to our mean call duration for Michigan H.
chrysoscelis. It is evident that regression lines, using Ralin’s equations for call
duration, would intersect when X =25C and Y =0.73 sec. Any possible
discrimination with respect to call duration for Ralin’s populations would appear to be
irrelevant at temperatures around 25 C.

Ralin (1977) indicated that the call duration for H. versicolor tended to be
intermediate between the duration of ‘‘eastern’’ and ‘‘western’’ H. chrysoscelis. Our
mean call duration for Michigan H. versicolor would be considered of intermediate
duration when compared with Gerhardt’s values for H. chrysoscelis (above). Ralin’s
regression equations for ‘‘southern’’ (Y = —0.04X + 1.62) and ‘‘northern’’
(Y = —0.03X + 1.44) H. versicolor would also produce intersecting regression
lines when X = 18 C and Y = 0.9 sec. Substituting our average temperature of
22.5 C for X in Ralin’s equations, we obtain values of 0.72 (‘‘southern’’) and 0.86
(‘‘northern’’). Neither of these values would be considered close to our mean call
duration for Michigan H. versicolor.

Pulse Repetition Rate

Pulse repetition rates were positively correlated with temperature for both H.
chrysoscelis and H. versicolor in Michigan (Fig. 2). The regression lines in Fig. 2
compare the Michigan populations with H. versicolor from Ralin (1977). Published
regression equations and pulse repetition rates are compared with Michigan
populations in Table 3. Hyla chrysoscelis in Michigan has a pulse repetition rate
which is most similar to ‘‘western’’ populations of H. chrysoscelis while Michigan
H. versicolor would be most similar to ‘‘northern’’ H. versicolor populations. Ralin
(1968, 1977) speculated that a greater pulse rate differential between H. chrysoscelis
and H. versicolor was evident in sympatric populations and this could be the result of
call reinforcement for pre-mating isolation. Most of the populations of H.
chrysoscelis in Wisconsin and Michigan do occur sympatrically with H. versicolor
and the greater distinction in the north might be attributed to reinforcement, but
analyses of large allopatric populations would be necessary to test this hypothesis. It
is evident that the slopes of the regression equations for H. chrysoscelis are all steeper
than those for H. versicolor (Fig. 2; Table 3). In Michigan, H. chrysoscelis
demonstrated a larger variance from the mean that did H. versicolor but, despite the

9

Hyla chrysoscelis

Pulses per second

20 21 22 23 24 25 26
Temperature C

Fig. 2 Pulse repetition rate for Hyla versicolor and H. chrysoscelis. Determinations are plotted from the
calls of Michigan male H. versicolor (dots) and H. chrysoscelis (circles). The regression lines for
Michigan H. versicolor and H. chrysoscelis (solid lines) are compared with ‘‘northern’’ and
‘“*southern’’ H. versicolor and ‘‘eastern’’ and ‘‘western’’ H. chrysoscelis (dashed lines) using the
regression equations provided by Ralin (1977).

variance, the probability that the slope for Michigan H. chrysoscelis is equal to the
slope for Michigan H. versicolor is very low (P = .0025).

Some of the variation shown in the regression analyses (Table 3) could be an
artifact produced by sample size used in the various studies or by the methods of
recording temperature. Larger sample sizes should result in smaller standard
deviations, confidence limit estimations and better correlations. Temperatures
recorded from the esophagus resulted in slightly less variance and slightly greater
correlations than did temperatures recorded from calling sites in Wisconsin (Jaslow
and Vogt, 1977).

Mean Dominant Frequency

The mean dominant frequency for Michigan H. chrysoscelis was higher than that for
H. versicolor (Table 2). Our regression equations (frequency vs temperature) were
not statistically valid and the ranges were wide. The actual measurement of dominant
frequency is complicated by the fact that these species have frequency modulated
(FM) pulses.

10

Table 3 Comparison of pulse repetition rate in Hyla chrysoscelis and Hyla versicolor popuiations.
Pulse rate (Y) at 24 C* is determined by substituting 24 for the temperature (X) in the
regression equations.

Mean pulse
Populations Regression repetition rate References
equation (pulses/sec @
24 C*)
Hyla chrysoscelis
Michigan a = 3:10 — 39,99 56.8 This study
Wisconsin Y= 2.59% — 2.90 59.3 Jaslow and Vogt (1977)
Texas Y = 2.36X — 3.40 33:2 Ralin (1977)
Texas and Missouri Y = 3.05X —_15.80 57.4 Gerhardt (1978)
Texas 55:1 Gerhardt (1974)
Georgia, South Carolina 44.6 Gerhardt (1974)
Oklahoma, Mississippi,
Georgia, South Carolina, Y= 27.88% — 21.75 47.4 Ralin (1977)
and North Carolina
New Jersey, Delaware Y =2.41X — 8.46 49.4 Zweifel (1970)
and Virginia
Hyla versicolor
Michigan ¥ = 1.32% — 7.50 24.2 This study
Wisconsin Y = 1.30X — 4.95 26.2 Jaslow and Vogt (1977)
New Jersey, Delaware Y = 1.43X — 7.16 27:2 Zweifel (1970)
New Jersey, New York Y = 1.22X — 4.30 25.0 Ralin (1977)
Texas Y=1.19XK — 0.51 29.1 Ralin (1977)
Missouri Y ='1,15XK. — __ 2:30 2.3 Gerhardt (1978)

* 24 C was chosen for comparative purposes in order to incorporate Gerhardt’s (1974) values which were
corrected to 24 C.

I]

Conclusion

The range map for H. chrysoscelis produced by Ralin (1968, 1977) must now be
amended to include Wisconsin (Blair, 1958; Jaslow and Vogt, 1977), Missouri
(Gerhardt, 1978), and Michigan. From the available evidence, Michigan H.
chrysoscelis has call characteristics which are most similar to ‘‘western’’ populations
and Michigan H. versicolor could be aligned with ‘‘northern’’ populations. A close
examination of the specimens and localities previously used for the distinction of
‘‘eastern’’ and ‘‘western’’ H. chrysoscelis or ‘‘northern’’ and ‘‘southern’’ H.
versicolor has, for the most part, relied on geographically similar populations
(perhaps, in some cases, the same recordings?) (See localities and acknowledgements
in Gerhardt, 1974, 1978; Ralin, 1968, 1977; Zweifel, 1970.) Previously, ‘‘western’’
populations were essentially central Texas populations. In the north, the ‘‘western’’
H. chrysoscelis ranges farther east than the Texas or Mississippi ‘‘eastern’’ H.
chrysoscelis .

The information from call duration and frequency indicates that there must be
considerable variation within and between populations and these parameters are
probably not as important as pulse repetition rate for discrimination. There appears to
be a greater divergence in pulse repetition rate between sympatric H. versicolor and
H. chrysoscelis in the north which may be the result of character displacement (Ralin,
1968, 1977). Analyses of additional populations, and especially allopatric northern
populations of H. chrysoscelis are needed before we accept Ralin’s tenet. Perhaps
populations from intermediate geographical areas will demonstrate clinal relation-
ships with respect to divergence in pulse repetition rate or slope when compared with
H. versicolor. Experimentally produced triploid hybrids are viable and do produce
adult males (Johnson, 1966; Bogart, unpublished) but, considering all the sympatric
populations of H. chrysoscelis and H. versicolor which have been studied, only one
‘‘intermediate call’’ of a putative hybrid has ever been reported (Zweifel, 1970).
Discrimination, therefore, does not seem to be a problem for the frogs. Future studies
from a larger number of populations in various regions will help to alleviate the
present problems concerning distribution and the call parameters which are actually
utilized by the populations for isolation, and possible intraspecific partitioning.

Acknowledgements

We thank Steve Fiering and Peter Tolson for help in the field, and David Green and
David Servage for helpful comments on the manuscript. Arnold G. Kluge and Joseph
T. Collins loaned museum specimens for nucleolar determination from the Museum
of Zoology, University of Michigan and the Museum of Natural History, University
of Kansas. We especially thank the staff at the Portage Lake State Park in Jackson
County. Research support for JPB is from the National Research Council of Canada.

12

Literature Cited

BLAIR, W. F.

1958 Mating call in the speciation of anuran amphibians. American Naturalist 92:27-51.
BOGART, J. P.

1968 Chromosome number difference in the amphibian genus Bufo: the Bufo regularis species

group. Evolution 22:42-45.

BOGART, J. P. and A. O. WASSERMAN
1972 Diploid-polyploid cryptic species pairs: a possible clue to evolution by polyploidization in
anuran amphibians. Cytogenetics 11:7-24.

BROWN, L. E. and J. R. BROWN
1972 Mating calls and distributional records of treefrogs of the Hyla versicolor complex in
Illinois. Journal of Herpetology 6:233-234.

CASH, M.N. and J. P. BOGART
1978 Cytological differentiation of the diploid-tetraploid species pair of North American treefrogs
(Amphibia, Anura, Hylidae). Journal of Herpetology 12:555-558.

FERNANDEZ-GOMEZ, M. E., J. C. STOCKERT, J. F. LOPEZ-SAEZ and G. JIMENEZ-MARTIN
1969 Staining plant cell nucleoli with AgNOs after formalin-hydroquinone fixation. Stain
Technology 44:48-49.

GERHARDT, H. C.

1974 Mating call differences between eastern and western populations of the treefrog Hyla
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13

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ISSN 0384-8159