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SONORAN HERPETOLOGIST 37 (4) 2024 181
Copyright © Notice: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Color Polymorphism and Individual Variation in Disparate Populations
California Red-legged Frogs (Rana draytonii)
Je A. Alvarez1, Jeery T. Wilcox2, Matt Coyle3, Maresa Scoeld3, and Tara Collins3,4
1The Wildlife Project, P.O. Box 188888, Sacramento, CA; je@thewildlifeproject.com
2Mitsiu Ranch Preserve, 3124 Sonoma Mountain Road, Petaluma, CA
3Westervelt Ecological Services, 600 N Market Boulevard, Suite 3, Sacramento, CA
4Madrone Ecological Consulting, 8421 Auburn Boulevard, Suite 248, Citrus Heights, CA
NATURAL HISTORY NOTE
The Linnaean system of taxonomy considered speciation
in wildlife as delimited by morphometric characterization,
geographic range (individuals of a species typically live
together), and overall morphology and patterning in
coloration. e concept followed the plan that if two
animals looked alike, they must be related (Larson 1968).
More recently, the biological species concept suggested
that appearance of two related individuals meant very
little and two very similar looking species may remain
seperate species irrespective of their similarities. is
can be found in cryptic species (i.e., Northwestern and
Southwestern Pond Turtles [Actinemys marmorata and
A. pallida]; Burroughs et al. 2024) as well as in Batesian
mimicry (Myers and Daly 1983). Conversely, individual
variation in a single species does not require speciation.
For example, Ensatina eschscholtzii eschscholtzii and E.
e. croceator, common in California, are the same species
(although dierent subspecies) and are markedly dierent
in appearance and can be syntopic (Stebbins 1957, Wake
et al. 1986). Individual variation in coloration is reported
in many species of garter snakes, and numerous species
of amphibians, such as California Tiger Salamander
(Ambystoma californiense), Black Salamander (Aniedes
avipuntatus), and Ensatina salamanders (Stebbins 2003,
Alvarez and Foster 2016). is appears equally true in some
anurans, where the Pacic Treefrog (Pseudacris regilla) and
the Sierra Nevada Yellow-legged Frog (Rana sierrae) showed
marked variation in coloration (Stebbins 2003, Jones et al.
2005).
roughout its range, from Mendocino County, south
to Baja California (Stebbins 1951) the California Red-
legged Frog (Rana draytonii) exhibits a variable coloration.
e original description by Baird and Girard (1852) was
brief: “e ground color is olivaceous green and maculated
with black on the upper region of the body and limbs.”
Storer (1925) gave greater detail in his description,
summarized here: referring to the dorsal coloration as
buy brown to olive brown, becoming darker posteriorly;
back and sides of the body covered in black blotches, each
with a light-colored central papilla, with these becoming
larger posteriorly (Fig. 1). He describes the ventral surface
as white with the undersides of the body, thighs, legs, and
feet covered in dragon’s blood red. ose researchers that
summarized the coloration following Storer (1925) were
predominantly similar (Slevin 1928, Stebbins 1966, 1985,
2003, Dodd 2013, Stebbins and McGinnis 2018). Stebbins
(1951) reported dark “dusky” blotches on the dorsum
with a fuzzy outline, a character that carries through to
adults from larval color patterning and one that became a
useful comparative diagnostic tool when invasive American
Fig. 1. Typical coloration of California Red-legged Frog (Rana draytonii) in both the adult life stage and the post-metamorphic life
stage, Napa County, CA. Photo by Je A. Alvarez.
The Linnaean
system of tax-
onomy consid-
ered speciation
in wildlife as
delimited by
morphometric
characteriza-
tion, geographic
range (individu-
als of a species
typically live
together), and
overall morphol-
ogy and pattern-
ing in coloration.
SONORAN HERPETOLOGIST 37 (4) 2024 182
Copyright © Notice: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)
Bullfrogs (Lithobates catesbeianus) became established.
Most anurans are capable of rapid color change due to
background matching to achieve crypticism in escaping
predators, possibly in thermoregulation, and to enhance
breeding colors (reviewed in Rojas et al. 2023). We
note an example of this where an adult California Red-
legged Frog that was captured from a pond bottom in
conditions where the air temperature was 5° C and the
surface water temperature was 6° C. e frog, probably
due to mobilization of melanophores from deep in its
dermal layers, presented with an atypical color; nearly
black. After approximately 3 minutes of exposure to the
sun, the ground color transmogried from dark purple
to a more typical coloration (i.e., Fig. 2). is drastic
color change is representative of short-term color change
due to physiological triggers, not a permanent color
polymorphism.
Atypical coloration (color polymorphism) has been
reported by Jansen and Alvarez (2022), and Solis-Sotelo et
al. (2022), reporting amelanistic and leucistic California
Red-legged Frogs respectively. ese reports described
individual frogs that were from geographically disjunct
locations (San Francisco Bay Area and northern Baja
California, respectively). e majority of frogs we have
encountered (n ≥ 150,000 individuals, unpubl. data) would
fall under the original description by Storer (1925; Fig. 1).
We report here on populations in which we found multiple
individuals with distinctive color polymorphisms.
e population with the widest range of color
polymorphisms is the Big Gun Conservation Bank,
Michigan Blu, Placer County, California—a site owned
and managed by Westervelt Ecological Services—where
over the past 16 years we have captured all life stages of
California Red-legged Frogs. Approximately half of the
captured frogs represented the typical adult coloration
(Fig. 1). A small percentage of frogs (approximately 10%)
were colored in an extraordinary pattern not representing
the typical coloration of California Red-legged Frogs in
any way (Fig. 3). ese individuals have an overall ground
color of black with a pattern of yellow, cream, gold, or
pink spotting (irregular shapes) over much of the dorsal
surface. ese atypically colored California Red-legged
Frogs appear more similar, visually, to some color morphs
of Sierra Nevada Yellow-legged Frogs (R. sierrae) than
they do California Red-legged Frogs (Stebbins 2003,
McGinnis and Stebbins 2018). Moreover, approximately
40% of frogs from Big Gun are colored in yet another
color polymorphism, with a suuse pattern of yellow
or cream spots covering the dorsum (Fig. 4). ese two
distinct color polymorphisms appear to be isolated to
this site, yet common to the Big Gun site, which has at
least three distinct variations (i.e., black with light ecks,
dominant gold color with dark braids of color, and typical
Fig. 2. Atypical coloration of a California Red-legged Frog (Rana
draytonii) seined from a cold pond bottom in winter, eastern
Contra Costa County, California. Note: this is not a color
polymorphism, but is likely mobilized melanophores, which can
return to a typical coloration in 0.5 to 3 minutes. Photo by Je A.
Alvarez.
Most anurans are
capable of rapid
color change due
to background
matching to
achieve crypti-
cism in escaping
predators, pos-
sibly in ther-
moregulation,
and to enhance
breeding colors
(reviewed in Ro-
jas et al. 2023).
Fig. 3. Two adult frogs with one typical coloration (right) and one (left) from the polymorphic forms at the Big Gun Site, Placer
County, California, referenced by Jeery T. Wilcox as the galactic form of California Red-legged Frog (Rana draytonii). Photo by Tara
Collins.
SONORAN HERPETOLOGIST 37 (4) 2024 183
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coloration), as well as individuals that appear to have one
or more of these color polymorphisms mixed together.
Two additional sites that do not exhibit the range of
color polymorphisms of Big Gun but are worth noting
because they represent geographically disparate populations
in dramatically dierent habitat types. e rst site includes
eastern Contra Costa County, CA (Kellogg Creek and
Brushy Creek watersheds), which are comprised of open
annual grasslands, on the eastern side of the Coast Range,
in northern California (see Alvarez et al. 2004). Small
proportion of the population includes individuals that have
a dorsum that is completely red (Fig. 5). An additional site
showing a color polymorphism falls in the southern extreme
of the range of the species, and is situated in a fen meadow
at 6,400 feet elevation in the Sierra San Pedro Mártir in Baja
California, Mexico. California Red-legged Frogs found here
are frequently noted to have a eld color of forest green, with
cream and gold highlights (Fig. 6).
Storer (1925) described a California Red-legged Frog
that changed color from nearly black to more typical
coloration, and back to nearly black in a matter of seconds.
is is similar to the frog we described as collected from a
cold-water source that modied its color within a couple
of minutes. is clearly shows that individuals can alter the
color of the skin in the context or temperature (our frog) or
stress (Storer 1925). We have further observed individuals
captured and placed in buckets, lighten their skin color
while housed out of the sun, again showing an ability to
contract and expand melanophores at a relatively fast rate.
We report this to note that variation in coloration can
be exemplied in an individual frog due to extrinsic and
intrinsic factors, as well as being a color polymorphism—
variation among individuals and populations.
It is not unusual to see high levels of variation in the
coloration of amphibians (Stewart 1974). Some species
have been misclassied, misidentied, or mismanaged
due simply to misunderstandings in the frequency and
occurrence of color variations (Paterson et al. 2016). We
acknowledge that early zoologists/naturalists like Storer
(1925) had a paucity of tools compared to modern
times. Early investigators took notes from live specimens,
when possible, but often had to work from preserved
specimens in museum collections (D. Wake, pers. comm).
In addition, for expediency, they picked a few specimens
from representative locations from which to draw the
species description. Modern researchers have the luxury of
capturing and distributing highly accurate color images,
allowing for highly varied descriptions of species range
wide.
e high level of variability in this species at Big
Gun may be phenotypic variation but further research
is required to make that determination. Whatever the
mechanism for this level of variation in a species, it shows
a persistently stable coloration pattern. At sites such as Big
Gun, which are over 1,000 m elevation, the California
Red-legged Frog could be misidentied as a Sierra Nevada
Ye ll ow -l e gg ed Fr og ( Rana muscosa) or an exotic species
Fig. 4. Adult California Red-legged Frog (Rana draytonii) from
one of three polymorphic forms at the Big Gun Site, Placer
County, California. Photo by Jeery T. Wilcox.
Fig. 5. Adult California Red-legged Frog (Rana draytonii) eastern Contra Costa County, CA illustrating an additional polymorphic
form. Photo by Je A. Alvarez.
Storer (1925)
described a
California Red-
legged Frog
that changed
color from
nearly black to
more typical
coloration, and
back to nearly
black in a mat-
ter of seconds.
This is similar
to the frog we
described as
collected from
a cold-water
source that mod-
ied its color
within a couple
of minutes.
SONORAN HERPETOLOGIST 37 (4) 2024 184
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that may then be targeted for control or removal. Biologists
working in these areas should be aware of the wide range in color
morphotypes that have the potential to be expressed in California
Red-legged Frogs, such as we have reported here.
Acknowledgments—Westervelt Ecological Services manages the
Big Gun Conservation Bank site and has generously oered access
to the site for many years. e Wildlife Project and Westervelt
Ecological Services supported the preparation of the manuscript.
We also acknowledge permitting through the California
Department of Fish and Wildlife (SCP-000040) and the US Fish
and Wildlife Service (TE-24524).
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