A cryptic new species of Indigo Snake (genus Drymarchon) from the

Transcription

Zootaxa 4138 (3): 549–569
http://www.mapress.com/j/zt/
Copyright © 2016 Magnolia Press
Article
ISSN 1175-5326 (print edition)
ZOOTAXA
ISSN 1175-5334 (online edition)
http://doi.org/10.11646/zootaxa.4138.3.7
http://zoobank.org/urn:lsid:zoobank.org:pub:C7391621-50DB-4070-9BCF-3D00B49F291C
A cryptic new species of Indigo Snake (genus Drymarchon)
from the Florida Platform of the United States
KENNETH L. KRYSKO1,5, MICHAEL C. GRANATOSKY2, LEROY P. NUÑEZ1,3 & DANIEL J. SMITH4
1
Florida Museum of Natural History, Museum Road, Dickinson Hall, University of Florida, Gainesville, Florida 32611 USA.
E-mail: KLK: [email protected], LPN: [email protected]
2
Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA.
E-mail: [email protected]
3
School of Natural Resources and Environment, 103 Black Hall, University of Florida, Gainesville, Florida 32611 USA.
4
Department of Biology, University of Central Florida, 4000 Central Florida Blvd, Orlando, Florida 32816, USA.
E-mail: [email protected]
5
Corresponding author
Abstract
Indigo Snakes (genus Drymarchon) occur from northern Argentina northward into to the United States, where they inhabit
southern Texas and disjunct populations in Mississippi, Florida and Georgia. Based on allopatry and morphological differences Collins (1991) hypothesized that the two United States taxa—the Western Indigo Snake, D. melanurus erebennus
(Cope, 1860), and the Eastern Indigo Snake, D. couperi (Holbrook, 1842)—deserved full species recognition. Building
upon this hypothesis with molecular and morphological analyses we illustrate that D. couperi is split into two distinct lineages. Based on the General Lineage Concept of Species, we describe the lineage that occurs along the Gulf coast of Florida and Mississippi as a new species, Drymarchon kolpobasileus. The new species is distinguished from D. couperi by a
suite of morphological features, including a shorter and shallower head, deeper and shorter 7th infralabial scales, and shorter temporal scales. Overall, the presence of a deep 7th infralabial scale provides the best univariate identifier of D. kolpobasileus sp. nov. This study illustrates the usefulness of using both morphological and genetic data in refining accurate
descriptions of geographical distributions.
Key words: Colubridae, D. couperi, D. melanurus, Drymarchon kolpobasileus sp. nov., Indigo Snakes, morphology, phylogenetics, Pleistocene, Pliocene, Serpentes, United States
Introduction
With the advancement of molecular and analytical tools, the definition of a species is becoming more agreed upon
among modern systematists (Wiens 2007; Pyron & Burbrink 2009). Although there have been more than 20
species concepts (some very similar) since Mayr’s (1969) Biological Species Concept, de Queiroz (1998, 2007)
made an invaluable contribution by taking common criteria among the different concepts and applying them to a
unified concept, the General Lineage Concept of Species. Under this philosophical view, the primary criterion for
recognizing a species is that it exhibits a separately evolved metapopulation or lineage, where an inclusive
population is made up of connected subpopulations in an ancestor-descendant series (de Queiroz 1998, 2007).
Secondary operational criteria (although not necessary) include that the lineage exhibits intrinsic reproductive
isolation, diagnosability, or monophyly, which may provide further evidence for lineage separation (de Queiroz
1998, 2007). Thus, species are well-supported genealogical lineages in terms of population structure (Wiens 2004;
Ereshefsky & Matthen 2005; de Queiroz 2007; Shaffer & Thomson 2007; Wiens 2007).
Indigo Snakes (genus Drymarchon, with five currently recognized species; see Wüster et al. 2001) occur from
northern Argentina northward into the United States, where they inhabit southern Texas and disjunct populations in
Mississippi, Florida and Georgia (Krysko et al. 2016). Based on known allopatry (approximately 1000 km, see
Moler 1992) and a difference in supralabial scale shape (Fig. 1; originally proposed by Baird & Girard 1853 and
Accepted by A. Bauer: 9 Jun. 2016; published: 18 Jul. 2016
549
illustrated by Conant 1958), Collins (1991) hypothesized that the two United States taxa previously considered as
subspecies within D. corais (Boie, 1827)—the Western Indigo Snake, D. melanurus erebennus (Cope, 1860), and
Eastern Indigo Snake, D. couperi (Holbrook, 1842)—deserved separate species recognition (Krysko et al. 2016).
The names D. couperi and D. melanurus have now been in use for more than 25 and 15 years, respectively (see
Collins 1991; Wüster et al. 2001; Wallach et al. 2014; and Powell et al. 2016). A recent multi-locus phylogenetic
study (Krysko et al. 2016) using both mitochondrial (mtDNA) and single copy nuclear (scnDNA) DNA suggests
that not only are D. melanurus and D. couperi genetically distinct and recognizable as separate species based under
the General Lineage Concept of Species, but also that D. couperi as currently recognized represents two distinct
genetic lineages and separate species (Fig. 2). These molecular data suggest that D. melanurus from Texas and
Mexico initially diverged from Drymarchon populations in Florida and Georgia about 5.9 million years ago (Ma);
95% Highest Posterior Density [HPD] = 2.5–9.8 Ma; during the late Blancan of the Pleistocene through the
Hemphillian of the Miocene) (Krysko et al. 2016). During this time, western Drymarchon likely utilized a Gulf
coast corridor and followed suitable habitat eastward during a glacial maximum when sea levels dropped and
previously submerged land on the Florida Platform was exposed (Krysko et al. 2016), a range expansion
hypothesis originally proposed by Auffenberg & Milstead (1965). Subsequently, the two well-supported genetic
lineages in Florida and Georgia (termed Atlantic and Gulf lineages after Soltis et al. 2006) had diverged from each
other about 2 Ma (95% HPD = 0.7–3.7 Ma; during the Irvingtonian of the Pleistocene through the Blancan of the
Pliocene) (Krysko et al. 2016). This later divergence illustrates a common biogeographic distributional break in
peninsular Florida, corresponding to historical sea level changes caused by Milankovitch cycles (Randazzo &
Jones 1997; Hine 2013; Krysko et al. 2016). The identified extreme glacial minimum between 2.7–3.2 Ma
incorporates much of the 95% HPD for the divergence date estimate between the Atlantic and Gulf lineages
(Krysko et al. 2016). During this time, sea level was about 22 m higher than present day (Miller et al. 2012) and
peninsular Florida consisted of a series of subaerially exposed islands on the Florida Platform (Lane 1994;
Randazzo & Jones 1997; Miller et al. 2012; Hine 2013; Krysko et al. 2016). Thus, Krysko et al. (2016)
hypothesized that the Gulf Lineage (as well as many other distinct plants and animals) evolved on these islands or
a single large island, which would have been surrounded by saltwater acting as a physical barrier to gene flow from
closely related populations (i.e., the Atlantic Lineage) still in contact with the mainland to the north. Despite
dozens of Milankovitch cycles (Hine 2013) along with associated forming of physical barriers (i.e., sea level
fluctuations, high elevation sand ridges, and/or insufficient habitats) since their initial lineage diversification, these
two lineages have likely come in and out of contact with each other many times, yet today they still illustrate near
discrete geographic distributions (Krysko et al. 2016).
Voucher specimens confirm that Drymarchon was once widespread in the Coastal Plain of the southeastern
United States, from southeastern Mississippi, southern Alabama, southern Georgia, and southward into the Florida
Keys (Krysko et al. 2010, 2016). Krysko et al. (2016) noted that the Alabama voucher consists of a late Pleistocene
fossil from the Bogue Chitto Creek Site, Dallas County (Dobie et al. 1996; Holman 2000), and only unverifiable
observations of live snakes have been reported from Alabama (Löding 1922; Haltom 1931; Neill 1954; Mount
1975). However, there is a single non-fossil specimen (MMNS 1199) collected on 16 November 1939 by W.H.
Young from southern Wayne County, Mississippi (United States Fish and Wildlife Service 2008; B. Jones, personal
communication). It is currently unknown to which lineage of Drymarchon this specimen is associated. This
specimen is one of three collected in Mississippi during a faunal survey directed by Fannye A. Cook from 1936–
1941; two specimens from Wayne County and a third specimen from Forrest County (Cook 1954; B. Jones,
personal communication). The other Wayne County specimen and the Forrest County specimen have been lost, and
the last Drymarchon in Mississippi was found in Forrest County in 1955 by William Turcotte (B. Jones, personal
communication).
Although both the Atlantic and Gulf lineages of Drymarchon are well-supported genealogical lineages in terms
of population structure (Krysko et al. 2016), a new species description was delayed in order to acquire secondary
operational criteria to provide further evidence for separately evolved lineages. In this paper, we conduct
morphometric analyses to illustrate reliably detectable diagnosable differences (in addition to molecular evidence)
between these two cryptic lineages, and revise the taxonomy of Drymarchon in the southeastern United States.
550 · Zootaxa 4138 (3) © 2016 Magnolia Press
KRYSKO ET AL.
FIGURE 1. Proposed differences in supralabial morphology between the A) Western Indigo Snake, Drymarchon melanurus
erebennus (Cope, 1860), and B) Eastern Indigo Snake, D. couperi (Holbrook, 1842), after Baird & Girard (1853). Illustrations
originally taken from Cope (1900) and modified after Conant (1958).
FIGURE 2. Bayesian inference phylogeny using combined mtDNA (cytochrome b and ND4 region) and scnDNA (NT3) for
Indigo Snakes (Drymarchon) in the southeastern United States. Values above nodes represent posterior probabilities, values
below nodes represent the mean divergence time estimation of the most recent common ancestor (MRCA) and time intervals in
parentheses representing 95% Highest Posterior Density (HPD). Representative images for Gulf Lineage UF-Herpetology
157097, Miami-Dade County, Florida; and Atlantic Lineage UF-Herpetology 169964, Saint Johns County, Florida. Modified
after Krysko et al. (2016).
Materials and methods
We examined specimens from the Academy of Natural Sciences of Drexel University (formerly Academy of
Natural Sciences of Philadelphia [ANSP]); Florida Museum of Natural History, University of Florida (UFHerpetology); and Mississippi Museum of Natural Science (MMNS) (Table 1).
The following standard scale counts and measurements were taken: snout-vent length (SVL)—measured with
a tape from the tip of the snout to the distal edge of the cloaca; ventrals—the number scales using the standard
system after Dowling (1951); subcaudals—the number of scales from the cloaca to the tail tip, excluding the tail
tip; supralabials—the number of enlarged scales bordering the upper lip (left/right sides); infralabials—the number
of enlarged scales bordering the lower lip; temporals and pre- and post-oculars—the arrangement of scales on both
sides of the head; and dorsal scale rows (DSR)—the number of scales one head length posterior to head, at midbody, and just anterior to the cloaca.
A NEW SPECIES OF DRYMARCHON FROM THE FLORIDA PLATFORM
Zootaxa 4138 (3) © 2016 Magnolia Press ·
551
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Statistical tests were first conducted to determine if data were normally distributed; if data were not normally
distributed a non-parametric test was used to determine the overall differences as well as test for sexual
dimorphism in ventrals, subcaudals, supralabials, and infralabials within and among Atlantic and Gulf lineages.
The numbers of temporals and DSR were used to describe variation only. These statistical tests were conducted
using SigmaPlot (ver. 11.0; Systat Software, Inc., Chicago, Illinois) with α = 0.05. Means are reported ± standard
error.
We also conducted an analysis to determine the legitimacy of Baird & Girard’s (1853) morphological diagnosis
between Drymarchon melanurus erebennus and D. couperi (Fig. 1). Conant (1958) illustrated that the 5th and 7th
supralabial scales were not in contact with each other in D. m. erebennus, whereas these scales contact each other
in D. couperi (sensu lato) (Fig. 1; see Baird & Girard 1853). We performed a Pearson’s chi-squared test to
determine if the frequency of this character varied significantly between these two species.
FIGURE 3. Illustration of the morphological variables collected. These measurements included head length (HL), head height
(HH), temporal length (TL), infralabial length (ILL), and infralabial height (ILH).
We also attempted to 1) determine morphological differences between the Atlantic and Gulf lineages of
Drymarchon couperi (sensu lato); and 2) assess the ability of such morphological measurements to categorize
specimens within a lineage from both areas where no molecular data are available, or in counties of collection that
contain both genetic lineages (Krysko et al. 2016). We restricted examination to linear measurements of head and
scale morphology. We took five linear measurements from each specimen (Fig. 3), including head length (HL),
head height (HH), temporal scale length (TL), 7th infralabial scale length (ILL), and 7th infralabial scale height
(ILH) using digital calipers (± 0.03 mm, Tresna Instrument IP67). To account for the effects of body size variation,
linear measurements were divided by the geometric mean of all linear measurements from that specimen
(Mosimann & James 1979; Granatosky et al. 2014a, 2014b). Prior to analysis, if the specimen originated from a
county of collection where molecular data was available and analyzed (Krysko et al. 2016), it was categorized as
either the Atlantic or Gulf lineage. If no molecular data were available from a county, or a county contained both
KRYSKO ET AL.
Atlantic and Gulf lineages, then the specimen was categorized by county of collection (Table 1). We conducted two
separate principal component analyses (PCA; correlation matrix) to summarize our morphological data. A PCA
was the preferred multivariate technique to explore variation in the metric data as well as to examine the
distribution of sample taxa in multidimensional morphospace (Neff & Marcus 1980; de Queiroz & Good 1997).
Additionally, we used a discriminant function analysis (DFA; unweighted linear method) to determine the
reliability of our morphological features in predicting lineage based on molecular data (Krysko et al. 2016). We
conducted separate DFA to determine if sexual dimorphism influenced the distribution of morphological features
rather than geographic location. Lastly, we used a cluster analysis (Ward hierarchical clustering) to assign
specimens to a particular lineage (i.e., Atlantic or Gulf) where no molecular data are available, or in areas that
contain both the Atlantic and Gulf lineages (Table 1).
To illustrate geographic distributions of our Drymarchon samples and lineages in the southeastern United
States, sample localities were georeferenced and plotted upon the Florida Platform along with the present day
coastline and state boundaries using ArcGIS version 10.1. On maps, our priority layers (highest to lowest) include
samples for each lineage based on 1) genetic data (Krysko et al. 2016), 2) morphological data from counties with
genetic samples, and 3) morphological data assigned into a specific lineage (i.e., Atlantic or Gulf) based on results
of the cluster analysis.
The first PCA and the DFA consisted of only specimens in which molecular distinction had been determined
(i.e., Atlantic or Gulf lineage). The second PCA, second DFA, and cluster analysis consisted of all Drymarchon
couperi (sensu lato) examined in this study. Measurements included in the PCA, DFA, and cluster analysis
consisted of HH, HL, TL, ILL, and ILH. In order to normalize the distribution data for each sample, each linear
variable included in the analyses was log transformed (Jungers et al. 1995; Hamrick 1999). Shapiro-Wilk and
Levene's tests were conducted to assure normality and equality of variances for the data. These statistical tests were
conducted in JMP Pro ver. 12 (SAS; Cary, NC).
Results
The mean number of ventrals was 188.36 ± 0.56 within the Atlantic (n = 30) and 187.00 ± 0.35 within the Gulf (n
= 71) lineages. There was a significant difference found in the mean number of ventrals (t = 2.069, d.f. = 99, P =
0.041) among Atlantic and Gulf lineages, and between males and females within the Atlantic (U = 22.5, P = 0.01)
and Gulf (t = -3.858, d.f. = 69, P = < 0.001) lineages.
The mean number of subcaudals was 63.89 ± 0.41 within the Atlantic (n = 19) and 64.22 ± 0.43 within the Gulf
(n = 36) lineages. There was no significant difference found in the mean number of subcaudals (t = -0.484, d.f. =
53, P = 0.631) among Atlantic and Gulf lineages, nor between males and females within the Atlantic (t = 1.112, d.f.
= 17, P = 0.281) and Gulf (Mann-Whitney Rank Sum test; U = 87.5, P = 0.135) lineages.
The arrangement of supralabials was 8/8 (n = 28 Atlantic, n = 67 Gulf), 7 + 8 (n = 1 Gulf), and 7/7 (n = 2
Atlantic, n = 3 Gulf). There was no significant difference found in the median number of total supralabials (MannWhitney Rank Sum test; U = 1053.0, P = 0.835) among Atlantic and Gulf lineages, nor between males and females
within the Atlantic (U = 66.0, P = 0.509) and Gulf (U = 432.0, P = 0.236) lineages.
The arrangement of infralabials was 9/9 (n = 30 Atlantic, n = 70 Gulf) and 8/8 (n = 1 Gulf). There was no
significant difference found in the median number of total infralabials (Mann-Whitney Rank Sum test; U = 1050.0,
P = 0.530) among Atlantic and Gulf lineages, nor between males and females within the Atlantic (U = 72.0, P =
1.000) and Gulf (U = 510.0, P = 0.556) lineages.
The arrangement of temporals was 2 + 2 invariant (n = 30 Atlantic, n = 71 Gulf), though many specimens had
smaller divided scales. The arrangement of oculars was 1 + 2 and invariant (n = 30 Atlantic, n = 71 Gulf). DSR
were 15-17-15 (n = 17 Atlantic, n = 29 Gulf), 17-17-15 (n = 12 Atlantic, n = 36 Gulf), and 17-19-15 (n = 1 Atlantic,
n = 5 Gulf).
The frequency of contact between the 5th and 7th supralabial scales varied significantly between Drymarchon
melanurus and D. couperi (sensu lato) (χ2 = 18.80; d.f. = 1; P < 0.001). Although 100% of D. couperi had the 5th
and 7th supralabial scales in contact with each other, only 80.96% of D. melanurus had these supralabial scales not
in contact.
555
FIGURE 4. Principal component analysis of head and scale measurements of Atlantic (blue) and Gulf (red) lineages of
Drymarchon in the southeastern United States. Bivariate plot of factor scores for the first two principal component axes of logtransformed shape variables. Convex hulls encapsulate all data points for a particular genetic lineage found by Krysko et al.
(2016).
Summary statistics for relative values of morphological data are presented in Tables 2 and 3. The results of our
second DFA, which aimed to determine if sexual dimorphism influenced the distribution of morphological features
rather than geographic location, misclassified 41.24% of the specimens. This finding indicates that effects of sexual
dimorphism are low in the features that we selected and likely do not interfere in the statistical reliability of the
other analyses.
Results from the first PCA are presented in Table 4 and Figure 4. Together the first two principal components
account for 70.1% of the variance within the sample. The first principal component axis accounts for
approximately 44.7% of the variance, and largely separates specimens based on molecular lineage classification
with little overlap between the two groups. Factor scores on this axis are most highly correlated with HL, HH, ILH
(negatively), and ILL. Based on the first principal component axis, specimens from the Gulf Lineage have
relatively shorter and shallower head dimensions, and relatively deeper and shorter 7th infralabial scales (Fig. 5). In
contrast, specimens from the Atlantic Lineage have relatively longer and deeper head dimensions, and relatively
longer and shallower 7th infralabial scales. The second principal component axis accounts for approximately 25.4%
of the variance, and to some extent separates specimens based on molecular lineage classification, but with
considerable overlap. Factor scores on this axis are most highly correlated with ILH (negatively) and TL. Based on
the second principal component axis, specimens from the Gulf Lineage have relatively deeper 7th infralabial scales,
and shorter temporal scales (Fig. 5). In contrast, specimens from the Atlantic Lineage have relatively shallower 7th
infralabial scales, and longer temporal scales. The results of the DFA appropriately classified 96.34% of the
examined specimens into the originally assigned molecular lineage groups based on the morphological characters
we examined.
KRYSKO ET AL.
557
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FIGURE 5. Differences in infralabial and temporal scale morphology between the A) Eastern Indigo Snake, Drymarchon
couperi (Holbrook, 1842), and B) Gulf Coast Indigo Snake, D. kolpobasileus, found in this study. Illustrations originally taken
and modified from Cope (1900). Note that D. kolpobasileus has relatively deeper and shorter 7th infralabial scales, shorter
temporal scales, and overall shorter and shallower head dimensions (not depicted).
TABLE 3. Summary statistics for morphological variables (mean ± standard deviation) arranged by species. All values
are presented as geometric shape variables.
n
Head length
Head height
Infralabial
height
Infralabial
length
Temporal
length
81
3.73 ± 0.24
1.51 ± 0.13
0.41 ± 0.04
0.58 ± 0.05
0.76 ± 0.09
Drymarchon couperi
42
4.09 ± 0.42
1.76 ± 0.17
0.30 ± 0.04
0.63 ± 0.04
0.75 ± 0.10
TABLE 4. Principal component analysis loadings for the first two axes performed on only specimens from the counties
from known lineages (Table 1) of Drymarchon in the southeastern United States. Measurements with significant loading
factors are in bold.
Measurement
Factor 1 (44.7%)
Factor 2 (25.4%)
HL
0.62
-0.10
HH
0.76
-0.10
ILH
-0.87
-0.50
ILL
0.68
-0.33
TL
-0.23
0.94
The second PCA largely reflected the results of the first PCA (Table 5; Fig. 6). Together, the first two principal
components account for 67.4% of the variance within the sample. The first principal component axis accounts for
approximately 41.4% of the variance and largely replicates the results of the first PCA. Specimens with high scores
on this axis display relatively longer and deeper head dimensions, and relatively longer and shallower 7th infralabial
scales. The second principal component axis accounts for approximately 26% of the variance and again replicates
the findings of the first PCA, with the exception that factor scores on this axis are also correlated with ILL
(negatively), ILH (negatively), and TL. Specimens with high scores on this axis display relatively shallower and
shorter 7th infralabial scale dimensions, and relatively longer temporal scales. Together the first two principal
components do, at some level, aid in interpreting potential lineage classification based on morphology in areas
where no molecular data are available, or in counties that contain both the Atlantic and Gulf lineages. For example,
the holotype of Drymarchon couperi (ANSP 3937) demonstrates morphology consistent with specimens from the
Atlantic Lineage. The Drymarchon specimen (MMNS 1199) collected from Wayne County, Mississippi
demonstrates morphology consistent with specimens from the Gulf Lineage. Florida specimens from Duval and
Madison counties exhibit morphology most similar to specimens from the Atlantic Lineage, whereas specimens
from Citrus, Columbia, De Soto, Dixie, Lafayette, Liberty, Sarasota, Seminole, Saint Lucie, Taylor, and Walton
counties exhibit morphology most similar to specimens from the Gulf Lineage. Specimens from Alachua, Clay,
559
Indian River, Hardee, and Volusia counties have morphological features consistent with both the Atlantic and Gulf
lineages. While PCA results allowed for specimens to occupy a morphospace intermediate between lineages, our
cluster analysis assigned all specimens to the Atlantic or Gulf lineage (Fig. 7). The assigned specimens matched the
genetic-predicted biogeographic distribution (Krysko et al. 2016), exhibiting evidence for separately evolved
lineages and secondary operational criteria for lineage separation (de Queiroz 1998, 2007).
TABLE 5. Principal component analysis loadings for the first two axes performed on all specimens of Drymarchon in
the southeastern United States. Measurements with significant loading factors are in bold.
Measurement
Factor 1 (41.4%)
Factor 2 (26%)
HL
0.64
-0.09
HH
0.67
0.19
ILH
-0.86
-0.50
ILL
0.64
-0.42
TL
-0.26
0.91
FIGURE 6. Principal component analysis of head and scale linear measurements of Atlantic (blue polygon) and Gulf (red
polygon) lineages of Drymarchon in the southeastern United States. Bivariate plot of factor scores for the first two principal
component axes of log-transformed shape variables. Convex hulls encapsulate all data points for a particular genetic lineage
found by Krysko et al. (2016). Stars represent holotype specimens for D. couperi (blue) and D. kolpobasileus (red).
KRYSKO ET AL.
FIGURE 7. Distribution of Indigo Snake (Drymarchon) samples on the subaerially exposed Florida Platform in Florida and
Georgia. Atlantic Lineage (blue triangles; with dots = genetic samples, without dots = this study using morphology based on
cluster analysis); Gulf Lineage (red circles; with dots = genetic samples, without dots = this study using morphology based on
cluster analysis); and stars represent holotype specimens for D. couperi (blue) and D. kolpobasileus (red). Genetic data taken
from Krysko et al. (2016).
Species accounts
Drymarchon couperi (Holbrook, 1842)
Eastern Indigo Snake
(Figures 8–9)
Coluber couperi Holbrook, 1842
Georgia couperi Baird & Girard 1853
Spilotes couperi (part) Cope 1860
Spilotes corais couperii (part) Lönnberg 1894
Compsosoma corais couperii (part) Cope 1900
Spilotes corais couperi (part) Brown 1901
Drymarchon corais couperi (part) Amaral 1929
Drymarchon couperi (part) Conant & Collins 1991
561
FIGURE 8. Holotype (ANSP 3937) of Eastern Indigo Snake, Drymarchon couperi, presumably from Wayne County, Georgia.
A) dorsal and B) ventral views.
Holotype. Academy of Natural Sciences of Drexel University (ANSP 3937); although there is no known collector,
locality, nor date assigned to this specimen, it is presumably collected by J.H. Couper (McCranie 1980), from the
Altamaha River (Baird & Girard 1853), Wayne County, Georgia, USA (Schmidt 1953).
Etymology. Drymarchon is derived from the Greek Drymos (meaning Oak Coppice or Forest) and archos
(meaning Commander or Chief), referring to it being the chief of the oak woodland. The species epithet couperi is
derived from the surname of J.H. Couper, who supposedly collected the holotype specimen.
Distribution. Occurs from southeastern Georgia, southward into Florida from Suwannee and Alachua
counties, southeastward to Marion, Osceola, and Indian River counties (Fig. 7).
Diagnosis. Drymarchon couperi is distinguished by a suite of molecular and morphological features, including
relatively longer and deeper head dimensions, longer and shallower 7th infralabials, and longer temporal scales.
Overall, the presence of a longer and shallow 7th infralabial scale provides the best univariate predictor for this
species (Table 3; Fig. 5). Based on both DNA (Krysko et al. 2016) and morphology (specimens examined in this
study) this species includes populations from southeastern Georgia southward along the Atlantic coast to central
peninsular Florida.
Description of holotype. Adult male; Total Length 163.1 cm; Snout-vent Length 133.1 cm; Tail Length 30.0
cm; Head Length 51.3 mm; Head Width 25.2 mm. The relative head length (geometric shape variable; see Tables 2
and 3) is short (3.80) and relative head height is narrow (1.98). Supralabials 8/8 (left/right); Infralabials 9/9;
Oculars 1+2/1+2; Temporals 2+2/2+2 (divided). The 7th infralabial is relatively long (0.65) and narrow (0.26)
(geometric shape variable; see Tables 2 and 3) and the temporal scale is relatively short (0.78). The 5th and 7th
supralabials are in contact with each other. Two pairs of chin shields, both of which are in contact with each other;
posterior pair slightly narrower than anterior pair. The rostral visible from above, broader than high. Dorsal scales
smooth and in rows at Mid-Body 17, Anterior 17 and Posterior 15; Ventral Scales 184; cloaca undivided;
Subcaudal Scale Total 59 (all divided).
The specimen has faded from its likely original solid black dorsum. There is light pigment (likely reddish in
real life) on the rostral, loreals, labials and chin shields that extend posteriorly onto the first three to four ventrals.
The first 40 ventral scales are mottled or bicolored with different degrees of black (posteriorly) and light colored
(distally) pigmentation with the remaining ventrals predominantly black. Subcaudals are entirely black.
Intraspecific variation. Ventrals range from 182–197 (mean = 188, n = 30); subcaudals range from 60–67
(mean = 63, n = 19); supralabials are arranged 8/8 (n = 28) and 7/7 (n = 2); infralabials are arranged 9/9 (n = 30);
temporals are arranged 2 + 2 (n = 30), some individuals with smaller divided scales; oculars are arranged 1 + 2 (n =
30); and DSR are 15-17-15 (n = 17), 17-17-15 (n = 12), and 17-19-15 (n = 1).
KRYSKO ET AL.
FIGURE 9. Holotype (ANSP 3937) of Eastern Indigo Snake, Drymarchon couperi, presumably from Wayne County, Georgia.
A) lateral, B) dorsal, and C) ventral views of head region.
563
Drymarchon kolpobasileus sp. nov.
Gulf Coast Indigo Snake
(Figures 10–11)
Spilotes couperi (part) Cope 1860
Spilotes corais couperii (part) Lönnberg 1894
Compsosoma corais couperii (part) Cope 1900
Spilotes corais couperi (part) Brown 1901
Drymarchon corais couperi (part) Amaral 1929
Drymarchon couperi (part) Conant & Collins 1991
Drymarchon kolpobasileus Krysko et al. 2016 (this study)
Holotype. Florida Museum of Natural History, University of Florida (UF-Herpetology 52751); collected by
Dennis M. Sargent in August 1981 on Mill Terrace and Riverwood Avenue, Sarasota, Sarasota County, Florida,
USA (27.29291 N, 82.52453 W, datum WGS84). Attacked by domestic dog and brought to Sarasota Jungle
Gardens where it died.
Paratypes. UF-Herpetology 55248, collected by T. Rooks on 6 June 1982 on State Road 24, 1.62 km SW State
Road 345, Levy County, Florida (29.225295 N, 82.953708 W); UF-Herpetology 78797, collected by Paul Elliot on
15 November 1988 at the entrance of Upper Hillsborough Wildlife Management Area, Pasco County, Florida
(28.35634 N, 82.12638 W); and UF-Herpetology 157096, collected by Joseph A. Wasilewski on 26 October 2006
at SW 204 Street and SW 134 Avenue, Miami, Miami-Dade County, Florida (25.57706 N, 80.40912 W).
FIGURE 10. Holotype (UF-Herpetology 52751) of Gulf Coast Indigo Snake, Drymarchon kolpobasileus, from Sarasota
County, Florida. A) dorsal and B) ventral views.
Etymology. The Greek kolpo (meaning Gulf, referring to the Gulf of Mexico) and Greek basileus (meaning
King) is used to form the composite noun kolpobasileus (Gulf King), which is applied as a noun in apposition to
the generic name Drymarchon. When sea levels were lower during the Pleistocene, D. kolpobasileus sp. nov. was
the largest known snake inhabiting the subaerially exposed Florida Platform that extended much further westward
than today. This species is still the largest native snake and king of the remaining exposed Florida Platform in the
western peninsula and panhandle of Florida.
Distribution. Known to occur along the Gulf coast in Wayne County, Mississippi; and in Florida from
Okaloosa County in the western panhandle, southeastward to Highlands, Putnam, and Seminole counties, eastward
to Indian River County, and southward to Miami-Dade and Monroe counties on the extreme tip of the southern
peninsula and Florida Keys. It is unknown if the single Pleistocene fossil from Dallas County, Alabama (Dobie et
al. 1996; Holman, 2000) is associated with Drymarchon kolpobasileus.
KRYSKO ET AL.
FIGURE 11. Holotype (UF-Herpetology 52751) of Gulf Coast Indigo Snake, Drymarchon kolpobasileus, from Sarasota
County, Florida. A) lateral, B) dorsal, and C) ventral views of head region.
565
Diagnosis. Drymarchon kolpobasileus sp. nov. is distinguished by a suite of morphological features including
relatively shorter and shallower head dimensions, relatively deeper and shorter 7th infralabial scales, and shorter
temporal scales (Fig. 5). Overall, the presence of a deep 7th infralabial scale provides the best univariate predictor of
D. kolpobasileus sp. nov. (Table 3). Based on both DNA (Krysko et al. 2016) and morphology (specimens
examined in this study) this species includes populations from the panhandle of Florida southeastward along the
Gulf coast to southern peninsular Florida, including the Florida Keys.
Description of holotype. Adult male; Total Length 232.1 cm; Snout-vent Length 194.8 cm; Tail Length 37.3
cm; Head Length 68.5 mm; Head Width 36.2 mm. The relative head length (geometric shape variable; see Tables 2
and 3) is short (3.40) and relative head height is narrow (1.59). Supralabials 8/8 (left/right); Infralabials 9/9;
Oculars 1+2/1+2; Temporals 2+2/2+2 (divided). The 7th infralabial is short (0.48) and broad (0.46) (geometric
shape variable; see Tables 2 and 3) and the temporal scale is relatively long (0.85). The 5th and 7th supralabials are in
contact with each other. Two pairs of chin shields, both of which are in contact with each other; posterior pair
slightly narrower than anterior pair. The rostral visible from above, broader than high. Dorsal scales smooth and in
rows at Mid-Body 17, Anterior 17 and Posterior 15; Ventral Scales 186; cloaca undivided; Subcaudal Scale Total
68 (all divided). The left hemipenis is everted.
The dorsum appears solid black from above. There is light pigment (likely reddish in real life) on the rostral,
labials and chin shields that extend posteriorly onto the first two ventrals. Each ventral scale is mottled or bicolored
with different degrees of black (posteriorly) and light colored (distally) pigmentation, with the last 8 ventrals
predominantly black. Subcaudals are entirely black.
Intraspecific variation. Ventrals range from 181–194 (mean = 187, n = 71); subcaudals range from 60–71
(mean = 64, n = 36); supralabials are arranged 8/8 (n = 67), 7/8 (n = 1), and 7/7 (n = 3); infralabials are arranged 9/
9 (n = 70) and 8/8 (n = 1); temporals are arranged 2 + 2 (n = 71), some individuals with smaller divided scales;
oculars are arranged 1 + 2 (n = 71); and DSR are 15-17-15 (n = 29), 17-17-15 (n = 36), and 17-19-15 (n = 5).
Discussion
Based on the results of the first PCA and DFA, morphological data support the differences between Drymarchon
couperi (Atlantic Lineage) and D. kolpobasileus sp. nov. (Gulf Lineage). Using only five linear measurements, we
were able to statistically separate these two species, and it is likely that further morphological examination will
result in a greater number of anatomical differences. Drymarchon kolpobasileus sp. nov. displays relatively shorter
and shallower head dimensions, relatively deeper and shorter 7th infralabial scales, and relatively shorter temporal
scales (Fig. 5). In contrast, D. couperi displays relatively longer and deeper head dimensions, relatively longer and
shallower 7th infralabial scales, and longer temporal scales. These characters are reliable morphological indicators
that classified 96.34% of our specimens into the appropriate geographic distribution based on genetic data (Krysko
et al. 2016). In fact, this successful classification based on morphology is more accurate at separating D. couperi
from D. kolpobasileus sp. nov., than is the long-standing known difference in supralabial morphology used to
distinguish D. melanurus erebennus from D. couperi (sensu lato) (Baird & Girard 1853; Conant 1958; Collins
1991), which was only present in 80.96% of our D. melanurus specimens. The single Mississippi specimen
displays all morphological features examined herein and occurs outside the range of D. melanurus, thus it was
assigned to our new species D. kolpobasileus.
It is reasonable to assume that the morphological features identified in this study may be useful in identifying
Drymarchon lineage affiliation in counties where no molecular data are available, or in counties that contain both
the Atlantic and Gulf lineages (Krysko et al. 2016). The results of our second PCA analysis do, to some extent,
show the applicability of using morphology as a tool to aid in lineage affiliation, although some areas (i.e.,
Alachua, Clay, Indian River, Hardee, and Volusia) are more difficult to interpret, and may represent areas of
hybridization between the two species. Following predictions based on our cluster analysis, morphological
variation closely follows biogeographic patterns predicted by Krysko et al. (2016) (i.e., specimens collected from
localities adjacent to those containing the Gulf Lineage tend to display morphology consistent with this lineage,
and vice versa in respect to the Atlantic Lineage). This should be interpreted with some caution however, as many
geographic localities are represented by few specimens.
In conclusion, our morphological analyses demonstrate that Drymarchon couperi (Atlantic Lineage) and D.
KRYSKO ET AL.
kolpobasileus sp. nov. (Gulf Lineage) can be distinguished from each other, and the morphological traits described
herein can be used as classifiers to aid in lineage identification. Our morphological data is consistent with genetic
data using both mtDNA and scnDNA (Krysko et al. 2016), and combining these two types of data provide a more
accurate geographic distribution for both species. Lastly, we believe that it is important to maintain natural genetic
diversity, especially with regards to conservation and translocation efforts.
Acknowledgements
We are extremely grateful to those who helped in this study. For contributing samples we thank Christopher L.
Jenkins, Dirk J. Stevenson, Becky Bolt, Kevin M. Enge, Paul E. Moler, Joseph A. Wasilewski, Peter A. Meylan,
Bob Zappalorti, Ray Ashton, Michael R. Rochford, Skip Snow, Nancy Russell, Christopher R. Gillette, Kenneth R.
Sims, S. Lloyd Newberry, Frankie Snow, Fred Antonio, F. Wayne King, John Jensen, Jim Garrison, Caitlyn
Staskiewicz, Mike and Kara Ravenscoft, William Cope, Steve A. Johnson, Carlos Iudica, Kim Annis, Daniel
Parker, Anthony Flanagan, Robin Lawson, Steven P. Christman, Steven Myers, Cindy Brashear Fury, Joshua
Holbrook, David Cockerill, Paige Martin, Phil and Karen Allma, Grant Lykins, Kendra Willet, Lisa Woods, Mark
E. Ludlow, Paul Russo, Valerie Sparling, Phil Frank, James Duquesnel, Jason Osborne, Mark Parry, Christopher J.
Lechowicz, Charles R. LeBuff, M. Wichrowski, Jens Vindum (CAS), Chris Austin, Donna Dittmann, Fred H
Sheldon, and Robb Brumfield (LSUMZ), Traci D. Hartsell (USNM), Alan Resetar (FMNH), Gregory WatkinsColwell and Kristof Zyskowski (YPM), Stephen P. Rogers (CM), Chris A. Phillips (UIMNH), Greg Schneider
(UMMZ), Travis LaDuc and David Cannatella (TNHC), John E. Simmons (KU), Darrel Frost and David Kizirian
(AMNH), Laura Abraczinskas (MSU); Ned Gilmore for taking photographs of the holotype (ANSP 3937) of
Drymarchon couperi; Bob Jones for data and taking photographs of the Drymarchon kolpobasileus specimen in the
Mississippi Museum of Natural Science; Elias Votzakis and Kurt Auffenberg for help forming the composite noun
kolpobasileus; Alexander R. Lounders for help taking scale counts and measurements; Roger W. Portell, Irvy R.
Quitmyer and Douglas S. Jones for Geology of Florida information; Claudia A. MacKenzie-Krysko for assistance,
attendance at indigo snake meetings, and loving support to KLK; Aaron M. Bauer and two anonymous reviewers
for constructive comments; Linda LaClaire for United States Fish and Wildlife permit (# TE221415-0USFWS);
and especially The Orianne Society Indigo Snake Initiative LTD and The Florida Fish and Wildlife Conservation
Commission (Project # 06011) for funding the phylogenetics study (Project # 08101301).
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