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2018 SOUTHEASTERN NATURALIST 172):286–292
Resolving Questionable Records of Pituophis ruthveni
(Louisiana Pinesnake)
Connor S. Adams1,*, Josh B. Pierce2, D. Craig Rudolph2, Wade A. Ryberg1, and
Toby J. Hibbitts1, 3
Abstract - Pituophis ruthveni (Louisiana Pinesnake) is considered one of the rarest snakes
in North America. For that reason, P. ruthveni is not well represented in scientific collections,
and each existing specimen is very important. Some museum records for the species
are considered questionable or unverified, especially those that represent extralimital records
or those from habitats not normally utilized by Louisiana Pinesnake. Clarifying these
questionable Louisiana Pinesnake records will ultimately provide a better understanding of
its historic and current distribution, which is necessary for listing decisions, critical-habitat
designation, and overall conservation efforts for the species. To resolve this uncertainty,
we performed a multivariate analysis using 13 morphological characters on 50 specimens
representing 3 snake groups: (1) P. ruthveni (n = 23), (2) P. catenifer sayi (Bullsnake; n =
23), and (3) questionable or unverified snakes (n = 4). We included Bullsnake because they
are sister to Louisiana Pinesnake genetically and also most morphologically similar. We
identified all questionable records of Louisiana Pinesnake examined as Bullsnake. Blotch
count, ventral-scale number, and scale-row number at mid-body were the most reliable
characters for distinguishing between groups. These results have potential conservation
implications for the species. The influence of these erroneous records could be substantial
in future research and conservation of the species due to the relatively few known specimens
of Louisiana Pinesnake. We recommend that the specimens we identified be annotated and
considered erroneous records.
Introduction
Pituophis ruthveni Stull (Louisiana Pinesnake) has long been considered one of
the rarest snakes in North America (Conant 1956, Rudolph et al. 2006, Stull 1940,
Young and Vandeventer 1988). Prior to recent efforts to determine the status of the
species, fewer than 100 records of Louisiana Pinesnake were represented in the literature
or in museum collections (Rudolph et al. 2006, Thomas et al. 1976, Young
and Vandeventer 1988). Currently, 246 Louisiana Pinesnake records are databased
by the US Forest Service (USFS) and the US Fish and Wildlife Service (USFWS;
J.B. Pierce, unpubl. data). This large, heavy-bodied snake inhabits pine savannahs
of the Gulf Coastal Plain west of the Mississippi River, and is historically reported
from 8 parishes in Louisiana and 12 counties in Texas (Dixon 2013, Dundee and
Rossman 1989, Werler and Dixon 2000).
1Natural Resources Institute, Texas A&M University, 1500 Research Parkway, College
Station, TX 77843. 2Southern Research Station, USDA Forest Service, 506 Hayter Street,
Nacogdoches, TX 75965. 3Biodiversity Research and Teaching Collections, Department of
Wildlife and Fisheries Sciences, Texas A&M University College Station, TX 77840. *Corresponding
author - conadams22scott@gmail.com.
Manuscript Editor: John Placyk
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Previous research concerning the conservation status of Louisiana Pinesnake has
suggested that the loss of frequently burned pine savannahs, especially the Pinus
palustris Mill. (Longleaf Pine) savannah ecosystem, is the driving factor of population
declines, and this species is now widely considered one of the most imperiled
snakes in the US (Reichling 1990, 1995; Rudolph et al. 2006; Young and Vandeventer
1988). Most of the Longleaf Pine ecosystem of the west Gulf Coastal Plains
was lost by the 1930s due to heavy logging within the region, and it has failed to
recover for a variety of reasons, including the decreased frequency of fire across the
landscape (Frost 1993). It is estimated that less than 5% of the original extent of this open
pine savannah ecosystem is extant, and much of that area is extensively altered by
changes in fire regimes, silvicultural practices, and conversion to other land uses
such as urban development and agriculture, which have further contributed to a reduction
in suitable habitat (Frost 1993, Rudolph et al. 2006). These circumstances
relegated remaining populations of Louisiana Pinesnake to isolated patches of
remnant forests, primarily on public lands, within the historic range of the species
(Reichling 1995; Rudolph and Burgdorf 1997; Rudolph et al. 1998, 2006).
Despite efforts to locate this species, it has only been found in 5 Louisiana parishes
(Bienville, Natchitoches, Rapides, Sabine, and Vernon) and 4 Texas counties
(Angelina, Jasper, Nacogdoches, and Newton) in the last 15 years (2000–2015)
(Rudolph et al. 2006). Although recent research has greatly improved our understanding
of Louisiana Pinesnake in regard to the natural history and current
distribution of the species, the evaluation of older records is still needed to confirm
its historic range. Louisiana Pinesnake specimens are not well-represented
in scientific collections, and some museum records are considered questionable or
unverified. Some of these records have been annotated, but uncertain records still
exist. Resolving these records could have a significant impact on future research
involving the conservation of this species.
Methods
To identify records that were considered questionable or unverified, we queried
a database maintained by the US Forest Service’s Wildlife Habitat and Silviculture
Laboratory located at the Southern Research Station in Nacogdoches, TX,
of all known Louisiana Pinesnake records. We identified 6 museum specimens of
Louisiana Pinesnake for which the authenticity of the specimens was considered
questionable or unverified (Table 1). These records included Louisiana Pinesnake
specimens collected from Houston, Montgomery, and Walker counties, in Texas;
and Beauregard, Calcasieu, and Jefferson Davis parishes, in Louisiana (Fig. 1).
We determined that an additional specimen from Caldwell County, TX, was questionable,
but it has since been resolved as a Pituophis catenifer sayi (Schlegel)
Bullsnake (Thomas et al. 1976). We performed a morphometric analysis using 13
morphological characters on correctly identified Louisiana Pinesnake and Bullsnake
specimens and on the aforementioned questionable snake specimens. We selected
Bullsnake for this comparison because it is very similar morphologically and also
considered sister to Louisiana Pinesnake (Rogriguez-Robles and Jesus-Escobar
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2000). These characters, which are known to vary between species, included blotch
count; rostral-scale length, height, and width; number of upper and lower labial
scales, ventral scales, and subcaudal scales; snout-to-vent length (SVL); total body
length (TBL); and scale-row number at neck, midbody, and tail (Reichling 1995,
Thomas et al. 1976).
The entire morphological analysis could not be completed for 2 of the questionable
Louisiana Pinesnake specimens. We could not examine the questionable
Figure 1. Map depicting specimen localities of verified and questionable Pituophis ruthveni
(Louisiana Pinesnake).
Table 1. Museum specimens of Pituophis ruthveni (Louisiana Pinesnake) examined in this study because
the authenticity was considered questionable. MSU = McNeese State University, TCWC = Texas
A&M University Biodiversity Research and Teaching Collections.
County or Collection Institution Catalog Specimen Updated
State Parish date code number Sex condition identification
Louisiana Beaureguard 20 Apr 1967 MSU 1339 Male Tail only Unknown
Louisiana Jefferson Davis Nov 1966 MSU 1274 Female Good Bullsnake
Louisiana Calcasieu 2 Sep 1988 SML 9291 N/A Photograph Bullsnake*
Texas Houston 5 May 1956 TCWC 14977 Female Good Bullsnake
Texas Montgomery Aug 1976 TCWC 81602 Female Good Bullsnake
Texas Walker 24 Apr 1976 TCWC 52078 Male Good Bullsnake
*per Thomas et al. 1976.
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Louisiana Pinesnake specimen from Beaureguard Parish, LA, because of its poor
condition (Table 1). We examined an additional questionable Louisiana Pinesnake
specimen from Calcasieu Parish, LA, via photograph from the original collector,
in which blotch count was the only measurement recorded (Williams and Cordes
1996). Based on blotch count only, we concluded that this specimen is most likely
a Bullsnake, according to criteria described in Thomas et al. (1976; Table 1). After
excluding these 2 specimens, we analyzed 50 specimens total: 4 considered
questionable specimens of Louisiana Pinesnake (Table 1), 23 verified specimens
of Louisiana Pinesnake , and 23 verified specimens of Bullsnake. We based our selection
of verified specimens on key characteristics and distributions. We included
only Bullsnakes collected from east of the Pecos River, in Texas, to avoid potential
influence from western subspecies and to ensure sister relationship to Louisiana
Pinesnake (Rogríguez-Robles and Jesús-Escobar 2000). We tested for differences
between the Louisiana Pinesnake (n = 23), Bullsnake (n = 23), and questionable
specimens (n = 4) groups described above using multivariate analysis of variance
(MANOVA) followed by pairwise comparisons among groups using Hotelling’s
post-hoc tests of significance. We also used principal components analysis (PCA)
to visualize the morphological characters that best distinguished between snake
groups. Prior to these analyses, we used ordinary least-squares regression to conduct
a residuals analysis that adjusted morphological characters for differences in
the body size (i.e., snout-to-vent length) of each specimen. Pair-wise Pearson correlations
among the size-adjusted characters revealed a significant correlation (R2 =
0.60, P < 0.05) between rostral-scale height and length, so we excluded the former
from our final morphometric analyses.
Results
The MANOVA revealed significant differences among groups of snakes (Wilks’
Lambda = 0.95, df1 = 22, df2 = 68, F = 6.93, P < 0.001). Hotelling’s pairwise
comparisons indicated that the verified Louisiana Pinesnake specimens were significantly
different from verified Bullsnake specimens (P < 0.001) and were also
significantly different from the unverified snake specimens (P < 0.01). The unverified
snake specimens were not significantly different from verified Bullsnake
specimens (P = 0.64). This pattern of statistical significance between snake groups
was apparent in the PCA (Table 2; Fig. 2). The first principal component axis explained
90.4% of the variation between snake groups with blotches, ventral scales,
and, to a lesser extent, scales at midbody exhibiting the highest loadings (PCA loadings
0.73, 0.66, and 0.17, respectively). Along this component, verified Louisiana
Pinesnake specimens were characterized by low blotch-counts, low ventral-scale
counts, and low scale-counts at midbody. Verified Bullsnake specimens and unverified
snake specimens exhibited high counts for each of those characters. Principal
component 2 explained the remaining variation between groups; blotches, ventral
scales, subcaudal scales, and tail-scale counts exhibited the highest loadings (PCA
loadings: -0.49, 0.49, -0.46, and 0.51, respectively; Table 2).
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Table 2. Loadings for each morphological character used in the principal components analysis (PCA)
illustrating multivariate differences between the Pituophis ruthveni (Louisiana Pinesnake), P. catenifer
sayi (Bullsnake), and unverified groups.
Morphological characters Axis 1 Axis 2
Blotch count 0.733 -0.487
Rostral-scale length -0.001 0.007
Rostral-scale width 0.048 0.054
Upper labial-scale number 0.025 0.108
Lower labial-scale number 0.010 -0.011
Scale-row number at neck 0.038 0.184
Scale-row number at midbody 0.166 0.066
Scale-row number at tail 0.016 0.509
Ventral-scale number 0.656 0.489
Subcaudal-scale number -0.014 -0.456
Variance explained 90.4% 9.6%
Figure 2. Results from principal components analysis (PCA) illustrating morphological
multivariate differences between Pituophis ruthveni (Louisiana Pinesnake), P. catenifer
sayi (Bullsnake), and unverified groups.
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Discussion
Our examinations of questionable museum records indicated that the unverified
specimens mentioned above are morphologically distinguishable from Louisiana
Pinesnake and represent Bullsnake. Based on these findings, the specimen records
from these counties and parishes (Houston, Montgomery, and Walker Counties, TX;
and Jefferson Davis Parish, LA) should be considered erroneous. Our data also suggest
that blotch count, ventral-scale number, and scale-row number at mid-body are
reliable characters for distinguishing between groups. Similar findings concerning
the taxonomy of snakes within the genus Pituophis exist in the literature (Conant
and Collins 1998, Reichling 1995, Thomas et al. 1976, Werler and Dixon 2000,
Wright and Wright 1957).
The provenance of these Bullsnake records is unknown. A large gap exists
between known Bullsnake distributional records and the westernmost Louisiana
Pinesnake records. It is unlikely that the Bullsnake specimens collected near the
distribution of Louisiana Pinesnake represent extant or natural populations, but
were probably errors made by the original collectors or represent escaped or released
pets.
Clarifying these questionable Louisiana Pinesnake records is important for
the conservation of the species. Erroneous records must not be used in future
habitat models; the influence could be substantial due to the relatively few known
Louisiana Pinesnake specimens (Wagner 2014). Knowledge of the species’ correct
historical distribution is vital to making informed listing decisions, critical habitat
designation, and the overall conservation efforts for the species.
Natural-history collections provide researchers with a useful tool to understand
the natural history and historical distributions of species (Shaffer et al 1998).
However, there is still a need for researchers to identify questionable or unverified
records, especially in rare species such as the Louisiana Pinesnake. There is a
wealth of information residing on the shelves of natural-history museums and in
their tissue collections that is underused or undervalued. Efforts to resolve questionable
records of species of greatest conservation need through morphometric or
genetic analyses (e.g., DNA barcoding) are necessary and important steps that will
ultimately contribute to better understanding of the historic and current distributions
of these species, as well as more informed decision making regarding policy,
conservation, and management.
Acknowledgments
We thank Dr. Justin Hoffman and Dr. Matt Kwiatkowski at McNeese State University
and Stephen F. Austin University, respectively, for allowing us to visit and examine museum
specimens. We are grateful to the American Museum of Natural History (New York, NY)
for specimen loans, Avery A. Williams for providing photographs of specimens, and Dalton
B. Neuharth and Aaron George for their help measuring specimens for this study.
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