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2012 SOUTHEASTERN NATURALIST 11(2):297–310
Phylogenetic Relationships in the North American Genus
Pseudemys (Emydidae) Inferred from
Two Mitochondrial Genes
Thomas G. Jackson, Jr.1, David H. Nelson1, and Ashley B. Morris2,*
Abstract - Pseudemys turtles are an important component of southeastern North American
aquatic ecosystems, but the relationships within the genus are poorly understood.
Convergent morphology and apparent hybridization have complicated the identification
of species boundaries and have resulted in numerous conflicting taxonomic treatments.
We used mitochondrial DNA sequence data from the control region and cytochrome-b
gene to address 1) the monophyly of currently recognized subgeneric clades (the cooters
and the red-bellies), and 2) relationships within these two groups. A total of 91 specimens
representing 8 Pseudemys and 3 outgroup taxa were sampled, and 36 distinct haplotypes
were recovered. Pseudemys forms a well-supported monophyletic group, but relationships
among species were not well resolved, such that support for the two subgeneric
groupings was lacking. Furthermore, most taxa do not appear to be monophyletic, with
the exception of P. gorzugi (Rio Grande Cooter) and P. texana (Texas Cooter), suggesting
the possibility of mitochondrial introgression as a result of historic or continuing hybrid
swarms across the range of the genus, or the lack of resolution may reflect a pattern of
recent speciation. In light of recent molecular surveys in turtles, the utility of mitochondrial
DNA in turtle systematics is also discussed .
Emydid turtles represent a significant component of the fauna of the southeastern
US. The family has been characterized as the most abundant, speciose,
and ecologically diverse group of turtles in eastern North America (Ernst and
Lovich 2009, Ernst et al. 1994, Stephens and Wiens 2003). Pseudemys is the
second largest genus of emydid turtles in the subfamily Deirochelyinae. Members
of this genus range from southeastern New Mexico eastward throughout the
Florida peninsula and as far north as Massachusetts (Fig. 1). Eight species and
two subspecies are currently recognized (Ernst and Lovich 2009): P. alabamensis
(Alabama Red-bellied Turtle), P. concinna (subspecies P. c. concinna [Eastern
River Cooter] and P. c. floridana [Florida Cooter]), P. gorzugi (Rio Grande
Cooter), P. nelsoni (Florida Red-bellied Turtle), P. peninsularis (Peninsula Cooter),
P. rubriventris (Northern Red-bellied Turtle), P. suwanniensis (Suwannee
Cooter), and P. texana (Texas Cooter). Most of these species, with the exception
of P. c. concinna, have restricted geographic distributions, and three are listed
on the IUCN red list (2010) as either lower risk/near threatened (P. gorzugi and
P. rubriventris) or endangered (P. alabamensis). The ability to properly plan for
conservation and management practices is obviously dependent on a clear understanding
of phylogenetic relationships, which is currently lacking in this group.
1Department of Biology, University of South Alabama, Mobile, AL 36688. 2Department
of Biology, Middle Tennessee State University, Murfreesboro, TN 37132. *Corresponding
author - email@example.com.
298 Southeastern Naturalist Vol. 11, No. 2
Seidel (1994) recognized two species complexes on the basis of morphological
and protein data: the red-bellies (P. rubriventris, P. nelsoni, and P. alabamensis)
and the cooters (P. c. concinna, P. c. floridana, P. gorzugi, P. peninsularis,
P. suwanniensis, and P. texana). Although Siedel and Ernst (1996) acknowledged
that these two lineages (i.e., red-bellies and cooters) are distinct, historical
problems with taxonomic nomenclature led them to avoid defining these two
groups as subgenera. The red-bellies are characterized as having orange-reddish
Figure 1. Geographic distribution of turtles in the genus Pseudemys: the red-bellies (subgenus
Ptechemys; upper map) and the cooters (subgenus Pseudemys; lower map), as defined by
Seidel (1994). Maps are redrawn from Ernst et al. (1994) and Conant and Collins (1998).
2012 T.G. Jackson, Jr., D.H. Nelson, and A.B. Morris 299
plastrons and a terminal maxillary notch bordered by tooth-like cusps. Turtles
in this group also have a prefrontal arrow formed by the meeting of the sagittal
head stripe with the supratemporal stripes (Carr and Crenshaw 1957, Ernst et
al. 1994, Leary et al. 2003). While members of the cooter species complex may
display some of the aforementioned characteristics of the red-bellies complex,
no one species exhibits all of these characteristics entirely. Lydeard (1996) stated
that “Pseudemys has been confounded by marked intra- and interspecific variation
in morphological features often used to delineate a species.” Hence, there
is considerable debate among many herpetologists as to the relationships among
the taxa in the genus. Additionally, multiple researchers have found evidence for
extensive hybrid swarms among species of the genus (Crenshaw 1965, Seidel and
Palmer 1991), which could explain the extensive history of taxonomic revision
described in Siedel and Ernst (1996).
While there have been several molecular studies that have included one or
more members of Pseudemys (Lydeard 1996, Stephens and Wiens 2003, Spinks
et al. 2009, Wiens et al. 2010), no study has yet included all recognized taxa in
the genus, nor has any study included more than one or a few accessions of each
sampled taxon. Lydeard (1996) used mitochondrial DNA (mtDNA) cytochrome-b
sequence data to determine if Mississippi individuals (n = 5) of P. alabamensis
should be recognized as a distinct lineage from those in Alabama (n = 2). He
included a small number of P. concinna (n = 6), P. c. floridana (n = 1), and P.
nelsoni (n = 1) for comparison, but failed to resolve any relationships among
the sampled taxa. Stephens and Wiens (2003) used morphology and the mtDNA
cytochrome-b and control region to address phylogenetic relationships across
Emydidae. They included seven Pseudemys taxa (P. alabamensis, P. concinna,
P. gorzugi, P. nelsoni, P. peninsularis, P. rubriventris, and P. texana) but only had
complete data for P. concinna. When all sampled taxa were included in a combined
morphological and molecular analysis, relationships within the genus were
poorly supported, with red-bellies (P. nelsoni, P. rubriventris, and P. alabamensis)
supported by only 53% bootstrap support (BS) using maximum parsimony
(MP), nested within the rest of the genus, which was only supported by 51% BS.
Spinks et al. (2009) used mtDNA cytochrome-b and seven nuclear loci (nucDNA)
to address relationships across the family, and they included four Pseudemys
taxa (P. c. concinna, P. c. floridana, P. nelsoni, and P. peninsularis). Each data
set (mtDNA and nucDNA) provided strong support for a monophyletic genus
(≥0.95 bayesian posterior probability [BPP] and ≥90% BS for both MP and maximum
likelihood [ML] analyses), but both were insufficient to address questions
regarding infrageneric taxonomy due to the limited number of taxa included.
Wiens et al. (2010) also used a combined mtDNA and nucDNA approach to the
family, and included seven Pseudemys taxa (P. concinna, P. gorzugi, P. nelsoni,
P. peninsularis, P. rubriventris, and P. texana). Their combined analysis showed
strong support (BPP 1.00) for the red-bellies (P. rubriventris and P. nelsoni; P.
alabamensis was not sampled), which were nested within the rest of the clade, as
was suggested by Stephens and Wiens (2003).
Considering the ecological importance and conservation concerns associated
with Pseudemys, additional molecular work is warranted. Our primary objective
300 Southeastern Naturalist Vol. 11, No. 2
was to significantly improve sampling within and among taxa in this group to
better address questions of relatedness. Previous molecular studies, which have
largely focused on broad-scale systematics in turtles, have yet to include all
recognized Pseudemys taxa and have typically included only one or two accessions
per taxon. As a first attempt at assessing phylogenetic relationships within
the genus, we chose to use mitochondrial DNA sequence data. In particular, we
were interested in assessing the monophyly of currently recognized infrageneric
groups (i.e., the red-bellies and the cooters), and relationships among taxa within
these two groups. Here we present the results of two mtDNA genes for 86 accessions
representing all recognized Pseudemys taxa, including subspecies, based on
the taxonomy of Ernst and Lovich (2009).
Materials and Methods
Samples were obtained through field trapping and from museum vouchers
(Table 1). Field samples were collected between May and August 2008. Four
sites in Alabama (Magnolia River [AL1], Blakeley River [AL2], Tensaw River
[AL3], and Fowl River [AL4]) and one site in Mississippi (West Pascagoula
River [MS1]) were chosen for sampling because they represented the full geographic
range of P. alabamensis (Fig. 2), which is a federally endangered species
and for which the authors have ongoing projects. With the exception of at the
Blakeley River site, turtles collected during this study were captured using
aquatic hoop traps. The traps were checked three days each week until a minimum
of 8–10 specimens of P. alabamensis were collected from each site. Any
other species of turtle trapped during this time were also sampled. Tail snips were
taken from captured specimens, along with physical measurements and voucher
photographs, and the turtles were released at the point of capture. The Blakeley
River samples were obtained from previously frozen specimens from an ongoing
highway mortality survey focused on P. alabamensis. Pseudemys species not obtained
through field sampling at the five sites described above were obtained from
museum voucher specimens. Bone fragments of P. nelsoni, P. peninsularis, P. rubriventris,
and P. suwanniensis were obtained from the collections of the Florida
Museum of Natural History (FLMNH), Gainesville, FL. Genomic DNA samples
for P. texana and P. gorzugi were obtained from M.R.J. Forstner at Texas State
University (TSU), San Marcos, TX. Blood samples of Chrysemys picta (Painted
Turtle) and Trachemys scripta (Pond Slider) were obtained from S. Graham and
G. Sorrell, Department of Biological Sciences, Auburn University, Auburn, AL,
and these species were used as outgroups for phylogenetic reconstruction. An
additional outgroup, Graptemys flavimaculata (Yellow-blotched Map Turtle),
was obtained through the field sampling described above. Collection data for all
samples included in phylogeny reconstruction are provided in Table 1.
DNA extraction, amplification, and sequencing
Total genomic DNA was extracted from tail snips and blood samples using
the Qiagen DNeasy Blood and Tissue Kit (QIAGEN, Valencia, CA) following the
manufacturer’s instructions. Bone sample preparation and DNA extraction were
2012 T.G. Jackson, Jr., D.H. Nelson, and A.B. Morris 301
Table 1. Specimens of each species surveyed for at two mitochondrial gene regions for phylogenetic
Collection data n Haplotype
Subgenus Ptechymys (red-bellies)
Pseudemys alabamensis Baur, 1893 (Alabama Red-bellied Turtle)
Magnolia River, Baldwin County, AL (AL1) 9 2, 4
Tensaw River, Baldwin County, AL (AL2) 6 3, 4
Blakely River, Baldwin County, AL (AL3) 7 4
Fowl River, Mobile County, AL (AL4) 6 4
Pascagoula River, Jackson County, MS (MS1) 11 1, 4
Pseudemys nelsoni Carr, 1938‡ (Florida Red-bellied Turtle)
Monroe County, fl(FL1) 1 19
Alachua County, fl(FL2) 2 20
Pseudemys rubriventris (LeConte, 1830)‡ (Northern Red-bellied Turtle)
York County, VA (VA1) 1 26
Virginia County, VA (VA2) 1 26
St. Mary’s County, MD (MD1) 1 27
Subgenus Pseudemys (cooters)
Pseudemys concinna concinna (LeConte, 1830) (Eastern River Cooter)
Magnolia River, Baldwin County, AL (AL1) 6 6, 7, 9, 11
Fowl River, Mobile County, AL (AL4) 2 5, 8
Pascagoula River, Jackson County, MS (MS1) 2 10
Pseudemys concinna floridana (LeConte, 1830) (Florida Cooter)
Magnolia River, Baldwin County, AL (AL1) 5 13, 14, 16
Fowl River, Mobile County, AL (AL4) 2 12, 15
Pseudemys gorzugi Ward, 1984† (Rio Grande Cooter)
Val Verde County, TX (TX1) 7 17, 18
Pseudemys peninsularis Carr, 1938‡ (Peninsula Cooter)
Marion County, fl(FL3) 4 21, 22, 23, 24
Manatee County, fl(FL4) 1 25
Pseudemys suwanniensis Carr, 1937‡ (Suwannee Cooter)
Suwannee County, fl(FL5) 1 28
Citrus County, fl(FL6) 2 29
Pseudemys texana Baur, 1893† (Texas Cooter)
Hays County, TX (TX2) 8 30, 31
Chrysemys picta (Schneider, 1783)* (Painted Turtle)
Macon County, AL (AL5) 3 32, 33
Graptemys flavimaculata Cagle, 1954 (Yellow-blotched Map Turtle)
Pascagoula River, Jackson County, MS (MS1) 1 34
Trachemys scripta (Schoepff, 1792)* (Pond Slider)
Macon County, AL (AL5) 2 35, 36
*Blood samples from S. Graham and G. Sorrell, Department of Biological Sciences, Auburn University,
†Total genomic DNA samples from M.R.J. Forstner Tissue Collection, Department of Biology,
University of Texas at San Marcos, TX.
‡Bone samples from Florida Museum of Natural History, University of Florida, Gainesville, FL.
302 Southeastern Naturalist Vol. 11, No. 2
completed at the University of Florida Interdisciplinary Center for Biotechnology
Research (UF ICBR). Prior to DNA extraction, bone samples were prepared
in a laminar flow hood to reduce any chance of cross-contamination of samples.
All samples were first washed in a 6% bleach solution, followed by two washes in
DNA-free water to remove any external contaminants. Samples were then placed
in 2-ml of 0.5M EDTA (pH 8.0) on a rocking mixer for 3–6 days until there were
signs of a gelatinous residue and opaqueness. Once the decalcification process
was complete, DNA was extracted using a phenol/chloroform protocol (Kemp
and Smith 2005) modified by B. Kimura (UF ICBR, unpubl. data).
Two mitochondrial regions, the 5’ end of the control region and cytochrome-b,
were selected for phylogenetic reconstruction. The primers selected for amplifi-
cation of the control region (CR-DES1 and CR-DES2) were initially developed
by Starkey et al. (2003) to study Chrysemys picta, a close relative of Pseudemys.
Cytochrome-b primers (mt-A and CR-12H) were originally designed by Lenk
and Wink (1997) for Emys orbicularis (L.) (European Pond Turtle; Emydidae).
PCR amplification of the two regions followed the methods of Kozak et al. (2005)
and Lenk et al. (1998), respectively. Annealing temperature was typically 55 °C,
although 47 °C was used for poor quality DNA samples with problematic amplifi
cations. Final concentrations for PCR reactions were the same for both regions:
1X PCR Buffer (Promega Corporation, Madison, WI), 3mM MgCl2, 200μM each
Figure 2. Trapping locations for the present study. Selected locations were designed to
cover the full geographic range of Pseudemys alabamensis. Sites are as follows: 1) Magnolia
River, AL, 2) Blakeley River, AL, 3) Tensaw River, AL, 4) Fowl River, AL, and
5) Pascagoula River, MS.
2012 T.G. Jackson, Jr., D.H. Nelson, and A.B. Morris 303
dNTP, 200nM of each primer, and 1.25 U GoTaq polymerase (Promega Corporation,
Madison, WI). Degradation of DNA from some bone samples required the
development of internal primers (Table 2) and lower annealing temperatures (47
°C) for amplification of both gene regions. PCR cleanup and DNA sequencing
were performed by High-Throughput Sequencing Solutions, a service of the
High-Throughput Genomics Unit, Department of Genome Sciences, University
of Washington, Seattle. All sequence data were deposited in GenBank (Accessions
Sequences were edited and manually aligned by eye using Sequencher 4.2
(Gene Codes Corporation, 1991–2004). Bayesian analyses were conducted using
Mr. Bayes 3.1.2 (Huelsenbeck and Ronquist 2001, Ronquist and Huelsenbeck
2003). Analysis of the combined data was performed, collapsing all individuals
with the same haplotype to a single representative. To improve the fit of the substitution
model to the data for Bayesian analysis, each gene region (control region
and cytochrome-b) was treated as a separate partition. While the hierarchical
likelihood ratio tests (hLRTs) are the most commonly employed model selection
strategy, Posada and Buckley (2004) suggest that the Akaike information
Table 2. Primers used to amplify two mitochondrial DNA regions (control region and cytochrome-b)
for turtles used in this study.
Primer name Primer sequence (5’ to 3’)
CR-DES 11 GCATTCATCTATTTTCCGTTAGCA
CR-DES 21 GGATTTAGGGGTTTGACGAGAAT
1Primers from Starkey et al. (2003).
2Primers developed in the present study for amplification and sequencing of bone samples. L = left
(or forward) primers, R = right (or reverse) primers; numbers refer to the nucleotide position of
the primers start location in relation to CR-DES1 or mt-A.
3Primers from Lenk and Wenk (1997).
304 Southeastern Naturalist Vol. 11, No. 2
criterion (AIC) is a superior approach. Therefore, the AIC was implemented in
Modeltest v3.6 (Posada and Crandall 1998) to determine an appropriate model of
evolution for each gene region. The TIM+I model of nucleotide substitution was
selected for the control region and the best-fit model of evolution for the cytochrome-
b region was K81uf+I. Two independent runs were performed to evaluate
the repeatability of estimating stationarity and convergence between runs. Each
run was set for 5,000,000 generations, sampling one tree every 1000 generations.
Stationarity was determined by plotting log likelihood scores against generation
times, and sample points collected prior to stationarity were eliminated (i.e., as
“burn-in”). The first 500 trees (10%) were discarded as burn-in, and the remaining
4500 trees were combined in a 50% majority rule consensus tree to estimate
posterior probabilities for supported nodes.
A total of 1450 bp from the control region and cytochrome-b gene region were
amplified for analyses. Ninety-one specimens from the eight different species of
Pseudemys and three outgroup taxa were used for analysis in this study. Of the 91
samples used, 36 different mtDNA haplotypes were recovered for the combined
mitochondrial data set (Table 1). Within the genus Pseudemys (n = 86), there
were 31 unique haplotypes, with no haplotypes shared across taxa. Pseudemys
concinna concinna exhibited the greatest variation in sequence data with seven
haplotypes represented from ten samples. Pseudemys alabamensis exhibited
four haplotypes from 39 specimens used for analysis. One haplotype (haplotype
4) was common among all the populations of P. alabamensis sampled. A single
private haplotype was observed in each of three sites (Magnolia River and Tensaw
River in Alabama, Pascagoula River in Mississippi). Together, the outgroups
accounted for five different haplotypes from six individuals.
Three major clades were recovered with Bayesian analyses (Fig. 3): Clade 1
contains P. gorzugi only; Clade 2 includes individuals from all species except
P. gorzugi, P. nelsoni, and P. texana; and Clade 3 includes individuals from all
species except P. rubriventris and P. suwanniensis. Each of these major clades is
supported by a Bayesian posterior probability of 0.98 or greater. Only P. gorzugi
and P. texana appear to be monophyletic, while all other species are polyphyletic
on the basis of the mitochondrial data presented here. There are no apparent
geographic trends with respect to distribution of haplotypes, with one exception.
Within Clade 3, there is a well-supported clade (PP 0.97) that includes all accessions
of P. nelsoni and all but one accession of P. peninsularis. These individuals
were all sampled from North Central Florida (see Table 1). The remaining accession
of P. peninularis falls within a well-supported (PP 0.98) sub-clade of Clade 2
that also includes P. suwanniensis and P. concinna concinna. Missing data likely
explains the inconsistent placement of this accession; 65 bp of the control region
that exhibited variation in other members of the genus were missing in this accession.
One accession of P. rubriventris from Maryland (MD1, haplotype 27) was
recovered as unresolved between Clades 2 and 3; this accession had 186 bp of
missing data in an otherwise variable region of cytochrome-b. Removal of these
2012 T.G. Jackson, Jr., D.H. Nelson, and A.B. Morris 305
twos accession did not significantly affect the positions of the remaining taxa in
the reconstructed topologies (data not shown).
Our results from two mtDNA regions show limited resolution among Pseudemys
turtles. Most taxa are not recovered as monophyletic, and there is no support
provided for currently recognized infrageneric groupings (i.e., red-bellies and
cooters). Pseudemys gorzugi and P. texana, which are the most geographically
distinct of all of the taxa, are the only recognized species recovered here as monophyletic
(BPP 1.00 in each case), although the position of P. texana nested within
the rest of the genus (BPP 1.00) is curious. Of the museum specimens included
Figure 3. Results of Bayesian analysis showing the relationship among the 31 unique
haplotypes of Pseudemys and the three outgroups. Numbers above each branch correspond
to posterior probabilities greater than 0.90 for each recovered relationship.
Parentheses contain haplotype codes (1–36), followed by sampling location, which correspond
to those given in Table 1.
306 Southeastern Naturalist Vol. 11, No. 2
here, most accessions of P. peninsularis and both accessions of P. nelsoni were
recovered in a single sub-clade of Clade 3 (Fig. 3). These two taxa share an
overlapping geographic distribution, making these accessions the only lineage in
our data set that appears to conform to any geographic pattern.
In some respects, these results are consistent with previous findings (Spinks
et al. 2009, Stephens and Wiens 2003, Wiens et al. 2010). However, our study is
the first to include substantial species-level sampling of all recognized members
of the genus. The patterns (or lack thereof) that we have recovered may reflect
the potential pitfalls associated with using only mtDNA in this group (see recent
review in Wiens et al. 2010). Alternatively, the lack of monophyly seen here may
reflect a long history of mtDNA introgression and widespread hybrid swarms. Either
way, taxonomic relationships within Pseudemys remain complex and elusive
and continue to warrant further work.
Potential pitfalls of mtDNA in Pseudemys
Mitochondrial DNA sequence data has long been the tool of choice for molecular
systematic and phylogeographic studies in animal taxa due to stability
of genome order, relatively high mutation rate, uniparental inheritance, and
ease of amplification (Avise 1994, 2000). In recent years, however, numerous
studies have identified a growing number of exceptions to each of the reported
advantages of mtDNA (see Galtier et al. 2009 for a recent review). As Galtier et
al. (2009) acknowledged, even with these potential pitfalls, mtDNA continues
to be the most practical first step to understanding molecular ecology of wild
populations. The practical applications of mtDNA are the reason we chose these
markers for addressing infrageneric relationships in Pseudemys, particularly
given the lack of previously published molecular data on the group.
Since the completion of the work presented here (Jackson 2009), Spinks et al.
(2009) and Wiens et al. (2010) reported significant conflict between mtDNA and
nucDNA in emydid turtles, suggesting that it would be inappropriate to depend on
mtDNA alone. However, neither study included multiple accessions of all Pseudemys
taxa. Spinks et al. (2009) actually commented on the fact that several taxa,
including Graptemys, Pseudemys, and Trachemys, are taxonomically problematic
and will need “extensive taxon and data sampling” to resolve relationships in
these groups. Wiens et al. (2010) suggested that their own results reflected actual
discrepancies between gene and species trees, but they were unable to invoke a
specific mechanism to explain this. They were quick to exclude introgression as an
option, but considering the limited sampling of Pseudemys taxa (single accessions
of six taxa), the chances of any obvious signs of introgression being recovered in
their molecular data set are limited. They also suggested that shorter-than-expected
branch lengths in mtDNA of Graptemys and Pseudemys may be the result of numts,
or mtDNA genes that have been transferred to the nuclear genome. However, they
have no empirical data to support this hypothesis, and Spinks et al. (2009) found
evidence for potential numts (polymorphisms within an individual mtDNA sequence)
in only four accessions out of approximately 70 taxa across the Emydidae
and related outgroups. While we cannot positively rule out the possibility of numts
in Pseudemys without extensive additional effort, we found no polymorphic sequences
within our accessions to suggest that this was an issue.
2012 T.G. Jackson, Jr., D.H. Nelson, and A.B. Morris 307
Evidence for introgression and hybrid swarms in Pseudemys?
Given that the issues above do not explain the observed patterns in Pseudemys
that are presented here, an alternative is needed. We suggest that historical and
potentially recent introgression as the result of widespread hybrid swarms may
be viable explanations. Wiens et al. (2010) argued that “recent, homogenizing
introgression across the genus” is unlikely, stating that many taxa sampled in
their study (P. gorzugi, P. nelsoni, P. rubriventris, and P. texana) are allopatric
and geographically distant from each other. While recent introgression may not
explain patterns in these particular species, mutations documented in mtDNA
sequences may actually reflect historical introgression that occurred following
glacial retreat in the Pleistocene, as has been hypothesized in many taxa across
the southeastern US (see Avise 2000, Soltis et al. 2006 for recent reviews).
As reviewed in Seidel and Ernst (1996), Pleistocene fossils of Pseudemys
are categorized as one of three taxa: P. nelsoni (known from Florida, Georgia,
Mississippi, and South Carolina), P. concinna (Georgia, Florida, South Carolina,
Alabama, Indiana, Kansas, and possibly Oklahoma), and P. peninsularis (Florida).
Additional reports of Pseudemys-like fossils from the Pleistocene of Texas
are reported in Holman (1964). There are also reports of Pseudemys fossils from
the Miocene and Pliocene of Florida (reviewed in Seidel and Ernst 1996). With
the caveat that the fossil record is likely an incomplete representation of Pleistocene
Pseudemys lineages, the existing records lead us to suggest that modern-day
taxa may be relatively young, such that they are exhibiting patterns of incomplete
lineage sorting of ancestral polymorphisms from their Pleistocene ancestors,
which were partially sympatric. For example, given the disjunct geographic
distributions of the three taxa included in the red-belly group (P. rubriventris,
P. nelsoni, and P. alabamensis), it is possible to hypothesize that these three
taxa may have arisen from a previously more widespread P. nelsoni as reflected
in the fossil record. A similar pattern is seen in the modern-day Sternotherus
oderatus (Latreille) (Common Musk Turtle; Kinosternidae), where three separate
phylogeographic assemblages (one in the Carolinas, one in Florida, and one
more interior/Mississippi River Valley) were recognized on the basis of mtDNA
restriction site data (Walker et al. 1997). Lamb et al. (1994) suggested that members
of the genus Graptemys (Emydidae), because of their reduced propensity for
terrestrial dispersal, may have experienced increased rates of allopatric speciation
caused by vicariant events that affected river habitats during the Pleistocene.
Similar events may be responsible for present-day distributions of Red-bellies in
the southeastern US. A detailed phylogeographic approach coupled with fossilbased
divergence time estimation (similar to that used in Spinks and Shaffer 2009
in Emys) may further clarify these patterns in Pseudemys.
Recent introgression may also play a role in some of the patterns observed
here. Crenshaw (1965) found evidence of extensive hybridization between
P. rubriventris and P. floridana in a lake in Richmond County, NC based on an electrophoretic
survey of serum protein and morphological analyses. Unfortunately,
much of Crenshaw’s discussion of putative hybrid zones in other regions (e.g., peninsular
Florida) is difficult to follow due to major changes in turtle taxonomy since
his publication in 1965. Arguments over the distinctiveness of P. c. concinna and
P. c. floridana at different locations across their sympatric ranges also allude to the
possibility of continuing or recent gene flow between these currently recognized
308 Southeastern Naturalist Vol. 11, No. 2
subspecific taxa (Jackson 1995, Seidel 1995). Microsatellite loci may prove more
effective at teasing apart historical and recent hybridization events in this genus.
As previously mentioned, three Pseudemys species are listed on the IUCN
red list (2010) as either lower risk/near threatened (P. gorzugi and P. rubriventris)
or endangered (P. alabamensis). Of these, only P. gorzugi was recovered as
monophyletic in the present study, although limited sampling and missing data
likely prevent us from being able to assess monophyly in P. rubriventris. We do
not, however, recommend changes to the taxonomy of these organisms on the
basis of the data presented here. The complex nature of the relationships within
Pseudemys remain difficult to resolve, and revisionary taxonomists should be
particularly cautious as a result.
We sampled extensively across the range of P. alabamensis, collecting a total
of 39 accessions from four locations in Alabama and one in Mississippi (Fig. 2,
Table 1). We found no support for the recognition of Mississippi populations as a
distinct evolutionary lineage, which was consistent with the findings of Lydeard
(1996). Furthermore, we found limited variation across the accessions sampled,
only recovering four distinct haplotypes within the species. This variation was
far less than expected for the sampling effort given the number of haplotypes
recovered within other sampled Pseudemys taxa (see Table 1). This result might
be a reflection of the extremely limited geographic range of the species and could
indicate a relatively small effective population size. Additional work is underway
to better understand reproductive ecology in this federally endangered species
(Hieb et al. 2011).
Phylogenetic relationships within Pseudemys are highly complex, likely as
a result of retained ancestral polymorphism and possibly recent hybrid swarms.
Such complexity warrants a battery of approaches, including multiple morphological
and molecular markers. Future work to resolve questions of relatedness in this
genus should focus their efforts on significant fine-scale sampling of sympatric and
allopatric populations of all recognized taxa. Furthermore, consideration of molecular
markers with different mutational rates (mtDNA/nucDNA sequences vs.
microsatellites) coupled with fossil calibration points will be necessary to better
comprehend underlying evolutionary processes from different points in time.
We thank K. Krysko for granting access to specimens from the FLMNH Osteological
Collection, and G. Clark and A. Gomez (UF ICBR) for assistance with molecular
work. We also thank M. Forstner and M. Gaston for contributing samples of P. gorzugi
and P. texana from the M.R.J. Forstner Tissue Collection. Specimens of T. scripta and
C. picta were provided by S. Graham and G. Sorrell. We would also like to thank J. Loo
and P. Floyd for their contributions during trapping efforts. Finally, we thank B. Kreiser,
G. Pauly, B. Thomson, P. Spinks, and several anonymous reviewers for their invaluable
comments on previous versions of this manuscript.
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