Cascabel

Genetically detecting bairdi-lindheimeri hybrids

A possible hybrid Pantherophis bairdi X P.o. lindheimeri from Bandera County, Texas.

Inevitably when the topic of hybrids/intergrades between Texas and Baird's ratsnakes comes up, someone always says something along the line of, "Well, let's just test their DNA and find out for sure."  This line of reasoning sounds quite logical, but it has always presumed that protocols for such determinations were already out there, just waiting to be applied to this very problem.  Now, however, such a technological solution appears to actually exist.

I perked up when I first saw the title of this new paper by Michael W. Vandewege and associates: "Evidence of Hybridization between Elaphe bairdi and Elaphe obsoleta lindheimeri Including Comparative Population Genetics Inferred from Microsatellites and Mitochondrial DNA."  Dealing with a topic near and dear to my heart, I quickly flipped through the pages to the beginning of the article.

Unfortunately, though, there is very little in this typically jargon-dense phylogenetic publication that will be of use - or even decipherable - to the average herper in the field.  To their credit, of course, this team has now established a protocol, using both mitochondrial and nuclear genes, that can be used in the laboratory to determine the genetic lineage of any questionable specimen of E. bairdi or E.o. lindheimeri one is likely to encounter in central or west Texas.

Vandewege et al. also managed to confirm the suspicions of earlier workers (e.g., Lawson and Lieb, 1990) that F1 hybrids between these two species are fertile and that backcrossing does occur, meaning that not every hybrid found will be a 50%-50% mixture of each parental species; the relative percentages of bairdi and lindheimeri in any given admixture can vary significantly.  They also determined that the issue of hybridization is limited to the zone of sympatry, consisting primarily of the south-central portion of the Edwards Plateau, and apparently does not affect populations of either species occurring outside of that zone.  Additionally, they have determined that whatever hybridization events are occurring are most likely the result of secondary contact and that these two lineages have been evolving independently and, therefore, are best regarded as full species, even though each is the other's closest relative.

All of the genetically identified hybrids detected in this study came from the Junction area of the South Llano River drainage in Kimble County (most drainages in the south-central portion of the Edwards Plateau appear to also harbor hybrids [see Lawson and Lieb, 1990, which remains the best morphological assessment of hybridization between these two species].  The authors report, however, that only five (8.9%) of their total sample of 56 specimens (most of which were collected in wide-ranging areas of central and west Texas, where hybrids would not be expected) showed genetic evidence of hybridization and they consequently conclude that such events (even in the zone of sympatry - the Junction area in this study) are "infrequent."  Since the authors found no hybrids outside of the zone of sympatry, however, it would seem to follow that the frequency of hybrids within the zone of sympatry must be >8.9%, although we are not provided with the total number of specimens from the hybrid zone.

As indicated in the earlier study of Lawson and Lieb (1990), morphological characters can be quite useful in detecting many cases of apparent hybridization between these two species, with the number of dorsal body blotches (mainly in juveniles) being absolutely diagnostic, where apparent (lindheimeri = 27-37; bairdi = 44-61).

Vandewege et al. sought to initially classify each of their specimens according to morphological characters provided by Olson (1977) for bairdi and by Burbrink (2001) for lindheimeri, although some of Olson's characters (e.g., # of supralabials, subdivision of genials, presence of stripes, etc.) were later shown to be of little diagnostic value by Lawson and Lieb (1990).  Based on morphology alone, three of the authors' 56 specimens were considered to be possible hybrids.  When the molecular data was analyzed, however, it actually showed that five specimens were genetic hybrids.  Significantly, the five genetic hybrids included the three that were detected morphologically.

Perhaps the most pragmatically refreshing aspect of this paper is the authors' insistence on retaining their "classically accepted" taxon names (i.e., Elaphe bairdi for the Baird's Ratsnake and Elaphe obsoleta lindheimeri for the Texas Ratsnake).  Note also that they chose to retain the subspecies name "lindheimeri," rather than dumping all populations to the west of the Mississippi into "Pantherophis obsoletus," as has become the fad among the majority of phylogeneticists nowadays.  This is especially so considering that the paper was published in the SSAR's Journal of Herpetology, which has a reputation for enforcing its own vision of standardized nomenclature.  Perhaps it was the authors' innocent yet bold statement that, since they consider the nomenclature of this genus to be "unresolved," - and, by implication, do not regard Burbrink (2001) to necessarily represent the final word on its phylogeny - it is appropriate to retain the more traditional taxonomic arrangement.

Literature Cited [unfortunately, I cannot find PDFs for any these papers]

Lawson, R., and C.S. Lieb. 1990.  Variation and hybridization in Elaphe bairdi (Serpemtes: Colubridae).  J. Herpetol. 24(3): 280-292.

Olson, R.E. 1977.  Evidence for the species status of Baird’s ratsnake.  Tex. J. Sci. 29(1): 79-84. 

Vandeweege, M.W., Rodriguez, D., Weaver, J.P., Hibbetts, T.D., Forstner, M.R.J., and L.D. Densmore, III. 2012.  Evidence of hybridization between Elaphe bairdi and Elaphe obsoleta lindheimeri including comparative population genetics inferred from microsatellites and mitochondrial DNA.  J. Herpetol. 46(1): 56-63.

Scent-trailing of lizards by Crotalus lepidus.

A Mottled Rock Rattlesnake (Crotalus l. lepidus) from the Davis Mountains of west Texas.

It has generally been assumed that small rattlesnakes, in which lizards comprise a significant portion of the diet, employ a different technique for subduing such prey; that is, that they strike and hold onto lizards (which pose little danger to the attacking snake), as opposed to the striking, envenomating, tracking behavior they use against small rodents, which are capable of defending themselves by biting.

Biologists Vicente Mata-Silva, Jerry D. Johnson, and Arturo Rocha of the University of Texas at El Paso were following a radio-transmitter-equipped adult male Mottled Rock Rattlesnake (Crotalus l. lepidus) at the university's Indio Mountain Research Station in Hudspeth County, Texas when they found the snake near a dying Greater Earless Lizard (Cophosaurus texanus).  That the lizard had been struck and envenomated was surmised from two bloody puncture wounds on its dorsal surface.  Shortly thereafter the snake began what was described as "frenzied" tongue-flicking searching behavior.  Locating the lizard, the snake grasped it by the head, dragged it beneath a nearby bush, and commenced the swallowing process.

Although C. lepidus undoubtedly frequently retains its hold on struck lizards, as conventional wisdom has long maintained, this observation indicates that they are equally capable of tracking down lizards that have been struck and released.

Mata-Silva, V., Johnson, J.D., and A. Rocha. 2011. Crotalus lepidus: Feeding behavior. Herpetol. Rev. 42(3): 439. 

Nuclear vs. mitochondrial genes in taxonomy

A recent phylogenetic study, by Adam D. Leache of the University of California at Davis, of 53 out of the 90+ species in the lizard genus Sceloporus employs four nuclear genes, which were contrasted against a new mitochondrial genealogy based on six genes, revealed more conflicting than concordant relationships among the 21 defined species groups.

Perhaps the most effective means of conveying these results is to simply reproduce Figure 4 from the paper, which clearly shows the level of disagreement between the two methodologies via a multitude of skewed dotted lines.  The tree derived from nuclear data is on the left, that from mitochondrial data to the right.  Bear in mind that this graphic is comparing species groups, not individual species (e.g., the Sceloporus graciosus species group is comprised of the three species: S. arenicolus, S. vandenburgianus, as well as S. graciosus itself).

 [Click on the image to enlarge]
The author concludes:

"The phylogenetic relationships inferred from the nuclear and mtDNA data are in strong disagreement (Fig. 4).  Conflicts are not restricted to weakly supported or unresolved nodes, but include relationships that receive strong support in the separate analyses . . . .  Furthermore, conflicts are found across different levels of the phylogeny and involve alternative placements for species groups and individual species. . . .

"Incongruence is not restricted to weak or unresolved nodes as might be expected under a scenario of rapid diversification . . ., but extends to conflicts involving clades receiving strong support (Fig. 4).  This latter type of incongruence indicates that the nuclear genes are tracking a species history that is distinctly different from that of the mtDNA genome. . . .

"Tapping into the nuclear genome to assemble data sets containing hundreds of independent markers offers greater potential for elucidating difficult phylogenetic relationships . . ., such as those presented by Sceloporus, than does continued sequencing of the remaining genes of the mtDNA locus." 

Some of the problems encountered when attempting to establish a phylogeny of Sceloporus are doubtless related to the hypothesized explosive radiation in its recent evolutionary history, which has resulted in an extensive and rapid diversification.  One remarkable mechanism which could play a role in rapid diversification among such groups involves the acquisition of differing numbers of chromosomes, which would of course instantly render these groups reproductively isolated from each other:

"Variation in chromosomes numbers is a particularly interesting feature of Sceloporus, because chromosomal changes can contribute to species formation . . . .  It is uncommon for members of a species group to have overlapping distributions; however, when communities of Sceloporus do form, they are generally composed of species with different chromosome numbers . . . .  This pattern suggests that chromosomal rearrangements may play a key role during lineage formation by establishing genetic incompatibilities between species . . . .  Whether the chromosomal changes observed in Sceloporus are adaptive is an open question, and the mechanism(s) responsible for increasing the rate of chromosome evolution in Sceloporus remain unknown."

The author additionally questions the wisdom of combining data obtained from nuclear and mitochondrial DNA for analysis, as most current studies utilizing nuclear genes are presently doing.

Leache, A.D. 2010. Species trees for spiny lizards (Genus Sceloporus): Identifying points of concordance and conflict between nuclear  and mitochondrial data.  Mol. Phylogent. Evol. 54(2010): 162-171.  [PDF]

 

 

Crotalus atrox confirmed as monotypic

Skeptics of the currently en vogue mitochondrial DNA sequencing techniques for generating phylogenetic trees have occasionally joked that even such an "obviously" homogeneous taxon as the Western Diamond-backed Rattlesnake (Crotalus atrox) would doubtless be split into several "cryptic" species if ever subjected to mtDNA-based study.  Imagine my surprise to discover that not only have a couple of such a studies been done, but that the results support the traditional notion of atrox as a relatively homogeneous species despite its broad range. 

Castoe, Spencer, and Parkinson (2007) sampled tissues of C. atrox from across its range (including Mexico but excluding peripheral populations in Nevada, Oklahoma, and Arkansas) for mtDNA sequencing.  Although numerous haplotypes were discerned during the study, most samples resolved into two clades ("Eastern" and "Western"), which are hypothesized to have diverged slightly from each other as a result of Pleistocene climatic cooling events pushing populations further to the south into refugia about 1.36 million years ago.  Prior to this, the Eastern and Western clades were apparently in contact along the Cochise filter barrier (roughly between the Animas and Chiricahua mountains in NM and AZ, respectively) and this contact has resumed in post-Pleistocene times.  This study also indicates that the Eastern clade experienced a much greater contraction during the Pleistocene than was experienced by the Western clade, but the Eastern clade currently occupies a substantially larger range than the Western one, implying a dynamic post-Pleistocene expansion in the east. 

Carol L. Spencer (2008), who was one of the investigators in the above mtDNA study, also conducted a complementary morphological study of C. atrox as part of her doctoral requirements at the University of Texas - Arlington.  Originally, Spencer collected measurements and counts of 68 morphological characters from 922 museum specimens of all age groups from throughout the range of the species.  The number of characters was then reduced to 37 by eliminating those that were repetitive or that showed no variation across specimens.  Counts and measurements of the juveniles were also eliminated because of purported high rates of variation among subadults and the fact that the proportions of various measurements may change from the juvenile to the adult stage.  This data winnowing left Spencer with information from 673 adults, which were then subjected to multivariate and univariate statistical programs for analysis.

The results of this analysis failed to show any appreciable patterns for most of the morphological characters investigated, although a number of east-west clines were detected, notably in a few scale counts, and a north-south cline in body size (which seems to differ from the conventional wisdom and which the author attributes to an adherence to Bergman's Rule).  Regardless of these clinal variations, the author found more variation within the three groups she investigated (Eastern, Central, and Western) than between them, effectively discounting the possibility that differentiation occurs along the most probable zone (the aforementioned Cochise Filter Barrier, which extends along the Continental Divide in SE AZ and SW NM).  This conclusion agreed with the previous mtDNA study (Castoe et al., above and op cit), which showed an intergradation of mitochondrial genes in that region, indicating that although different haplotypes had developed during their more southerly Pleistocene sequestration, both clades had been freely interbreeding since their post-Pleistocene reintroduction to each other. 

These two studies offer up an example of what we should see more of in herpetological taxonomy: the application of various, complementary methodologies to a problem instead of making a quixotic decision to disturb taxonomic stability based upon a single study involving a technique (mtDNA sequencing) that is becoming increasingly suspect when compared to results from other methods.  The chauvinism exhibited by molecular taxonomists towards other (especially morphological) methods tends toward an unscientific incuriosity in many cases.  All morphological characters are, after all, determined by nuclear DNA, not by mitochondrial DNA, and it is becoming increasingly evident that mitochondrial DNA  sequencing is inadequate (by itself) to detect many intraspecific populations and subspecies that are "obvious" in a cursory morphological inspection.  Additionally, I am becoming increasingly suspicious that the "phylogenetic history" recorded within the two respective genomes (mitochondrial and nuclear) will eventually prove to be significantly different for most species. 

Literature Cited

Castoe, T.A., Spencer, C.L., and C.L. Parkinson. 2007.  Phylogeographic structure and historical demography of the western diamondback rattlesnake (Crotalus atrox): A perspective on North American desert biogeography.  Molecular Phylogenetics and Evolution 42(2007): 193-212.   [PDF]

Spencer, Carol L. 2008.  Geographic variation in Western Diamond-backed Rattlesnake (Crotalus atrox) morphology.  Pp. 55-78.  In Hayes, W.K., Cardwell, M.D., Beaman, K.R., and S.P. Bush (eds.). 2008.  The Biology of Rattlesnakes. Loma Linda, CA: Loma Linda Univ. Press, xvi + 606 pp., 20 color plates.   [PDF]

Effectiveness of "aquatic barriers" in semi-aquatic species

A persistent question always arises when reading phylogeographic studies of herp distribution: how effective are putative riverine "barriers" (e.g., especially the Mississippi and Apalachicola systems) at limiting gene flow between members of species that are distributed across them?

Such herpetological phylogeographic studies as currently exist tend to indicate that for more terrestrial forms (e.g., Pantherophis obsoletus complex, P. guttatus complex, Coluber constrictor, Lampropeltis getula, etc) these river systems significantly impede the exchange of at least mitochondrial genes between populations located on either side of such drainage systems (regardless of the well-known fact that all known species of snakes possess the innate ability to swim).

As would be expected, however, the evidence of a barrier effect is much more equivocal when semi-aquatic species are investigated.  Agkistrodon piscivorus (Guither and Burbrink, 2008) and Nerodia erythrogaster (Makowsky et al., 2010), for example, both display extensive (mitochondrial) gene flow across such river systems, implying that they are less effective barriers for such semi-aquatic species than for more terrestrial forms. 

A new study from M.C. Brandley et al. has sought to specifically address this question with the large water snake Nerodia rhombifer, which they characterize as one of the most aquatic North American water snakes, "spending the majority of its time in or near freshwater environments and consuming fish almost exclusively (97% of its diet . . . .)".  The authors investigated the phylogeographic structure of this species via a "time-calibrated" phylogenetic analysis of mitochondrial DNA using tissue samples from 388 specimens collected throughout the current range of the species in the USA.

The results of the study indeed indicate the presence of distinctive haplotypes to the east and west of the Mississippi River.  However, especially along the river itself, there were several populations composed of a mixture of the eastern and western haplotypes, leading the authors to conclude that, while the Mississippi River did not function as a complete barrier in N. rhombifer, it nevertheless influenced mitochondrial gene flow to the extent that characteristic mt haplotypes managed to develop on both sides of the river.

The authors further suggest that although the Mississippi is - or has been - only a partial barrier (i.e., a "filter") to N. rhombifer, much of the mitochondrial divergence detected in this study occurred relatively recently during the early Pleistocene, likely during interglacial periods when the river was much wider than currently.

The curious failure of the Mississippi River to serve as an impediment to either Agkistrodon piscivorus or Nerodia erythrogaster while exerting at the same time a detectable filter effect on the equally or even more aquatic N. rhombifer remains unexplained by this paper although the authors proffer the possibilities that either 1) mtDNA markers are not sensitive to the signs of vicarience in A. piscivorus and N. erythrogaster, or 2) that these species have invaded the areas west of the river too recently to be detected by mtDNA, or 3) that ultimately the river has not truly acted as an impediment to either of these species.

 This paper is a refreshing, relatively noncontroversial application for mtDNA techniques in a venue that is perhaps more appropriate for them than some of the intraspecific "analyses" in which they are currently employed.  Fortunately, no traditional subspecies were available to be sunk as a result of this study, but one must wonder, if only cynically, if the authors were philosophically inclined toward the recognition of subspecies, whether they might have described their eastern and western clades of N. rhombifer as some sort of "mitochondrial subspecies"!

Brandley, M.C., Guiher, T.J., Pyron, R.A., Winne, C.T, and F.T. Burbrink. 2010.  Does dispersal across an aquatic geographic barrier obscure phylogeographic structure in the diamondback water snake (Nerodia rhombifer)?  Molecular Phylogenetics and Evolution 57(2010): 552-560. 
PDF =   http://www.naherpetology.org/pdf_files/1664.pdf

Literature Cited

Guiher, T.J. and Burbrink, F.T. 2008. Demographic and phylogeographic histories of two venomous North American snakes of the genus Agkistrodon.  Mol. Phylogenet. Evol. 48: 543-553.  PDF = http://www.naherpetology.org/pdf_files/1024.pdf

Makowsky, R., Marshall, J.C., Jr., McVay, J., Chippindale, P.T. and L.J. Risssler. 2010. Phylogeographic analysis and environmental niche modeling of the plainbellied water snake (Nerodia erythrogaster) reveals low levels of genetic and ecological differentiation. Mol. Phylogenet. Evol. 55 (2010): 985-995.  PDF = http://www.naherpetology.org/pdf_files/1498.pdf

Arizona Treefrog threatened by Bullfrogs

(Photo by Randy Babb, courtesy of the Reptiles and Amphibians of Arizona website:  http://www.reptilesofaz.org/Turtle-Amphibs-Subpages/h-h-wrightorum.html )

Two Arizona Game and Fish Department non-game biologists recently reported in Herpetological Review that the introduced and invasive Bullfrog (Lithobates catesbeianus) has been documented to prey upon Arizona Treefrogs (Hyla wrightorum) that occur in a disjunct, isolated population in the Huachuca Mountains and Canelo Hills.

In July of 2008 Thomas Jones and Ross Timmons collected two adult Bullfrogs from a small temporary pond where H. wrightorum were calling.  One of the Bullfrogs contained four adult treefrogs, while the other contained three.  Given that treefrog breeding sites in this population may consist of only 2-30 adults of this high elevation species, it is apparent that the presence of the highly predatory Bullfrogs may comprise a serious threat to the much smaller treefrogs.

The biologists also speculated that since all of the sexable Hyla recovered from the Bullfrogs' stomachs were males, the Bullfrogs may have been using the sounds of the chorusing male treefrogs to hone in on their small temporary breeding ponds.  Alternatively, it is possible that the female treefrogs simply had not yet arrived at the ponds since these observations were made early in the monsoonal breeding period.

Bullfrogs are not generally considered to be a high elevation species (these observations were made at 1890 m [6200 ft]), and considering their extended larval phase, are somewhat of a surprising predator in an area where most potential breeding ponds are seasonal at best.  Jones and Timmons, however, note that the Bullfrogs have managed to breed for several years in a permanent, spring-fed pond near the head of the canyon where the predation occurred.  Even more ominously, the biologists assert that the Bullfrogs are capable of quickly covering great distances during the summer monsoon season, which would allow them to temporarily occupy other treefrog breeding sites, potentially depleting them also. 

This disjunct population of H. wrightorum, has recently been declared a "candidate" for listing under the Federal Endangered Species Act and this observation provided the first documentation of the threat previously suspected to be posed to the Arizona Treefrog by this rapacious introduced predator. 

Fortunately, Jones and Timmons were engaged in an effort to remove Bullfrogs from the canyon when these observations were made and, considering their findings, such activity must be continued if not redoubled if we hope to assure the continued existence of the beautiful little Arizona Treefrog in this herpetologically fabled area. 

Jones, Thomas R. and Ross J. Timmons. 2010. Hyla wrightorum: predation.  Herpetol. Rev. 41(4): 473-474.

Book Review: Manny Rubio's Guide to the Rattlesnakes of the US and Canada.

Rubio, Manny. 2010. Guide to the Rattlesnakes of the United States and Canada. Rodeo, NM: ECO Herpetological Publishing and Distribution. 307 pp, w/copious color photos and maps.  ISBN: 0978897943. Softcover, $34.95

I have to confess that Manny Rubio's new rattlesnake book had me at the first glimpse of the beautiful portrait of an Arizona Ridge-nosed Rattlesnake that adorns its cover.  Issues of judging books by their covers aside, however, this new work by a well-known rattlesnake aficionado and professional photographer provides a tremendous amount of information that would be difficult to gather together elsewhere.  The fact that it is also adorned by the author's outstanding photographic skills merely ices the proverbial cake.  That said, however, it would be particularly remiss for a review on a herpetological site such as this to gloss over a few shortcomings and picky details. 

Rattlesnakes as a group have been well covered in the herpetological literature, beginning with Gloyd's  The Rattlesnakes, Genera Sistrurus and Crotalus (1940).  Klauber's magnum opus, Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, has continued through three editions of (1956, 1972, and 1997).  More recently Campbell and Lamar's treatise, The Venomous Reptiles of the Western Hemisphere (2004), which though not restricted to rattlesnakes, managed to cover all the taxa of Crotalus and Sistrurus known at the time.  Hubbs and O'Connor (2009) have also produced a new endeavor, which this reviewer has not yet seen, and the trend currently culminates with the present work, which follows some twelve years in the wake of Rubio's critically acclaimed Rattlesnake: Portrait of a Predator (1998).  While most of these books are not exactly "popular" fare and would hardly qualify as "field" guides, Rubio's new book comes close in both size (9" X 6") and content, making it all the more unfortunate that the author has chosen to restrict himself to the comparatively well-tilled soil north of the Mexican border.     

Contrary to most specialized guides, which use their additional space to delve into identification esoterica (and even minutiae) not possible in the more generalized works, Rubio has assumed the stance of deemphasizing such details in the conviction that all US and Canadian rattlers can be sufficiently distinguished simply by viewing their photos and consulting the range maps in this book.  To this end, it must be admitted that Rubio has provided excellent arrays of photos for each species and subspecies that would likely fulfill this goal to at least a 95% level (the few instances where this might not be practical are noted in the text). 

Some of the characters that Rubio has chosen to eliminate or deemphasize are: head scalation, number of scale rows at points along the body, number of ventral scales, hemipenial morphology, venom pharmacology, and properties of mitochondrial DNA.  The explanation given for excluding this data revolves around the requirement for handling, close inspection, and/or chemical/molecular analysis that applying such criteria would entail.  Admittedly, few serious avocational rattlesnake aficionados ever actually resort to these characters in practice; still, it would have been comforting for them to have been included.

Taxonomically this book adheres to the version of orthodoxy currently accepted as of its date of publication with one exception: Rubio continues to recognize the Hopi Rattlesnake (Crotalus viridis nuntius).  It is of course the author's prerogative to recognize this subspecies despite its sinking by the most recent review (Douglas et al, 2002; based solely on mtDNA sequencing), but it would have been interesting to know his rationale, although such might arguably exceed the scope of the book.  Also, in the Timber Rattlesnake account, Rubio reasonably brings up the unsatisfying current solution to the taxonomic problems inherent in this species (i.e., that no subspecies are justified), while reiterating how distinctive the "Canebrake" and "Timber" "morphs" really are (at least east of the Mississippi).

Scientific names are also generally in agreement with current standards except for the omission of the admittedly antiquated double "i" patronyms for mitchellii and edwardsii, as written in their original descriptions and thus required by International Commission on Zoological Nomenclature.

Additionally, although the author professes an intention to use the common names deemed standard by the three major herpetological societies in North America (Crother et al, 2008), he fails to do so consistently, using the preferred hyphenated form "Diamond-backed" initially but later lapsing into "Ridgenose," sans hyphen.  Rubio also uses the peculiar formulation of "Green Prairie Rattlesnake" for Crotalus v. viridis and later the atypical "Spotted Rattlesnake" for Crotalus pricei (although the accepted "Twin-spotted" adjective is used in the subspecies account).  These are relatively minor discrepancies, however, and unlikely to confuse most readers.  Rubio is to be commended for writing the common names as proper nouns and appropriately capitalizing them; there is a difference in meaning between, for example, "twin-spotted rattlesnake" and "Twin-spotted Rattlesnake."

Each of the eighteen species accounts begin with a page-length summary for the species and/or each subspecies (in the case of polytypic forms).  Especially helpful to neophytes, the scientific name for each taxon is immediately followed by a pronunciation guide, a feature all too rare in books of this sort (although purists and Europeans will doubtless find fault with the author's decision to retain the markedly American tendency to pronounce the "-i" ending of patronyms with a long "i" [e.g., "klauber-eye"]). 

The first section of each taxon summary is dubbed "Features at a Glance," and depicts the silhouette of an average-sized individual snake juxtaposed against a human boot print on one side and a six-foot linear scale on the opposite, providing an effective representation of the relative length of each form.  Following this graphic are several one sentence descriptors of the taxon's salient physical characteristics (e.g., size, rattle audibility, general pattern characters, etc.).

The second part of the summary page covers "Disposition & Venom Potential."  Here each form is assigned a general threat level indicated by from one to five red skull-and-crossbones icons (Crotalus adamanteus rates five icons, Sistrurus miliarius only one).  Next is a very general one sentence description of the temperamental tendencies of each form (experienced herpers will of course recognize that there are many exceptions to these generalities).  This section closes with another one sentence evaluation of how "life threatening" the author considers a bite from each form, ranging from "extremely serious" (e.g., C. adamanteus), "very serious" (e.g., C. atrox), "serious" (e.g., C. cerberus), "possibly lethal to children or unhealthy adults" (e.g., C. willardi and C. pricei), to "not known to be lethal" (e.g., S. miliarius). 

"Conservation Status & Population Threats" comprises the next section of each summary page where the author attempts to divine the status of each form, with most appearing to fall into the "declining throughout range" category.  Curiously, Crotalus willardi and C. lepidus are both included in the "declining throughout range" group, whereas Crotalus pricei is listed as "stable throughout range.  The "population threats" listed for most taxa are somewhat redundant, with litanies of "commercial collecting" and "unwarranted killing" appearing surprisingly more frequently than "habitat destruction" and "commercial development."

The "Habitat" section of each summary page consists of a brief general description of the kinds of natural situations known to be favored by each form.

And the last item on each summary page is a small map (ca. 1.5" X 1.5") depicting the range of each species (with each subspecies in a different color).  These maps can also become quite redundant in polytypic species, with exactly the same map repeated on consecutive pages (that's five successive pages in the Crotalus oreganus complex displaying the same map!). 

At the end of the species accounts Rubio undertakes to remedy what is likely the most frequent identification conundrum among rattlesnakes north of the Mexican border: the distinction between C. atrox and C. scutulatus.  Devoting three pages and ten photos to this problem, Rubio produces ten characters that generally serve to differentiate between the two similar forms.  Surprisingly, however, he fails to include among those characters one that I have personally found to be extremely reliable: the "Rich G. Rule," that the basal segment of the rattle is almost always uniformly black in C. atrox and usually much lighter or bicolored in C. scutulatus.

The range maps are a mixed bag, depicting substantial gaps in distribution where none that would justify inclusion on maps of this small scale actually exist (e.g., C. lepidus in Central and W. Texas) and continuing to show the presence of taxa in areas where they have been virtually extirpated (e.g., C. adamanteus in the Florida Parishes of Louisiana).  An improvement over similar such maps in most field guides, however, is the attempt to depict how truly spotty the distributions of many rattlesnakes actually are in the modern landscape, particularly in the more developed areas of the country. 

Nonetheless, it appears problematic as to how accurately these splatterings of color represent real populations as opposed to merely suggesting spotty distributions (e.g., the distribution of C. horridus in Arkansas is shown as consisting of fairly evenly dispersed specks, whereas the truly disjunctive distribution of the same species in east Texas is shown with a continuous swath of color).  The map for the Northern Mohave Rattlesnake (C. s. scutulatus) is also particularly helpful in that it depicts the relative distribution of the two major - and medically significant - toxins to be found in this form (although the uninitiated must ultimately infer the legend of the map from the text).

The textual accounts for each of the species is thoroughly up-to-date and well-written, covering the significant details of natural history that would not conveniently fit on the summary pages.  One feature of the text that this reviewer found somewhat irritating, however, was the spacing of the text itself; placed almost as though it was double-spaced, the text was not nearly as compact as it could have been, creating the impression of wasted room that could have been profitably used to include a few more North American taxa - doubtless this was due to the layout designer rather than the author. 

As is virtually required for any work dealing with venomous animals, Rubio deals with the potential of envenomation by repeating the accepted modern view of first aid for such situations: there is basically no effective emergency treatment other than seeking medical attention as soon as possible.  Similarly he deals with those who will inevitably be tempted to keep rattlesnakes by painting clearly the medical, financial, and possibly legal consequences of doing so.

All in all, with these few minor criticisms aside, Manny Rubio and ECO Herpetological Publishing and Distribution have created another worthy addition to their growing library of literature produced by herp enthusiasts for herp enthusiasts; it is highly recommended for anyone with an interest these iconic and fascinating creatures.  

Literature Cited

Campbell, J. A. and W.W. Lamar. 2004.  The Venomous Reptiles of the Western Hemisphere. (2 vol.).  Ithaca: Cornell Univ. Press.  870 pp. 

Crother, B. I. (ed.). 2008. Scientific and Standard English Names of Amphibians and Reptiles of North America North of Mexico, with Comments Regarding Confidence in Our Understanding. (6th ed.).  SSAR Herp. Cir. 36, 84 pp.

Douglas, M.E., Douglas, M.R., Schuett, G.W., Porras, L.W. and A.T. Holycross. 2002.  Phylogeography of the Western Rattlesnake (Crotalus viridis) complex, with emphasis on the Colorado Plateau, pp. 11-50, In Schuett, G.W., Hoggren, M., Douglas, M.E. and H.W. Greene [eds.]. 2002. Biology of the Vipers.  Eagle Mountain Publishing.  xii + 580 pp. + 16 plates.

Gloyd, H. K.  1940.  The rattlesnakes, Genera Sistrurus and Crotalus.  Chicago Acad. Sci. Special Publ. (4): 1-266.

Hubbs, B.R. and B.P. O'Connor. 2009. A Guide to the Rattlesnakes of the United States.  Tempe, AZ: Tricolor Books.  96 pp.

Klauber, L. M. 1956. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, 2 Vol.  Berkeley: Univ. of California Press.  1476 pp.

Klauber, L. M. 1972. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, 2nd ed., 2 Vol.  Berkeley: Univ. of California Press.  1533 pp.

Klauber, L. M. 1997. Rattlesnakes: Their Habits, Life Histories, and Influence on Mankind, 3rd ed., 2 Vol. (Foreword by H. W. Greene), Berkeley: Univ. of California Press.  1580 pp.

Rubio, Manny. 1998. Rattlesnake: Portrait of a Predator. Washington, D.C.: Smithsonian Institution Press.  272 pp.

Kisatchie Corn

Snake, that is. 

 

  

 

 

It’s a rare event when I plan a herping excursion to an area seeking specific forms and actually manage to find at least one of them.  The Kisatchie Corn Snake shown here recently managed to somewhat relieve that nemesis.

 

 

Long known to herpetological hobbyists as the “Kisatchie Corn Snake” from its prevalence in west-central Louisiana’s Kisatchie National Forest, this form has remained taxonomically controversial over the years.  Until relatively recently, the Kisatchie Corn has generally been regarded as simply a drably colored population of the usually garish Corn Snake (Pantherophis guttatus), although some have suggested that it is in fact an intergrade population between eastern (P. g. guttatus) and western (P. g. emoryi, the Great Plains Rat Snake) races of a more widely distributed single Corn Snake species. 

 

Adding to the controversy is the recent description of this form as a full species, Slowinski’s Corn Snake (Pantherophis slowinskii) by Frank T. Burbrink (2002 [PDF]).  Burbrink’s data is based largely upon mitochondrial DNA sequencing and a strongly held conviction that large rivers – especially those such as the Mississippi – should constitute evolutionary barriers, despite the well-known fact that all snakes can swim. 

 

While Burbrink’s mtDNA analysis did reveal a clade indigenous to the west-central Louisiana area but closely related to the eastern group, his findings are diminished by the fact that he had no tissues from other areas where this form allegedly occurs in much closer proximity to the very similar Great Plains Rat Snake (P. emoryi), such as southern Arkansas, SE Oklahoma, and eastern Texas (Burbrink, in fact, states that P. slowinskii occurs no further south in Texas than the Brazos River, which we now know it does, perhaps expressing his fixation with rivers again). 

 

At any rate, this turn of events reinforces my contention that one should avoid rushing to adopt the latest taxonomic innovations.  Burbrink’s paper is only a single test of this hypothesis.  Proper scientific methodology requires that sound theories (in the scientific sense) should not be synthesized from only a single investigation.  Indeed, in such controversial situations, adoption of taxonomic change could – and should – await further research that would either validate or refute Burbrink’s conclusions. 

 

Despite all of this, both of the organizations purporting to seek standardization of common names and taxonomic nomenclature in American herps (Center for North American Herpetology and the SSAR-HL-ASIH Committee [PDF]) immediately accepted Burbrink’s alteration of the taxonomy in this group (it should be pointed out that Burbrink is a member of the latter group – perhaps not the best tactic in avoiding the appearance of conflict of interest). 

 

As for my personal opinion, I have no trouble in recognizing this distinct population taxonomically, however I feel that it is currently more appropriate at the subspecies level (i.e., Pantherophis guttatus slowinskii) than as a full species. 

 

Ironically, though, the category of subspecies is currently out of favor among reptile taxonomists, some even curiously arguing that it is “uninformative.”  Composed mostly of molecular systematists enslaved by the dogmas of cladistics, modern phylogeneticists apparently ignore the subspecies category simply because their espoused doctrines and methodologies lack techniques to deal with it.   

  

Burbrink, Frank T.  2002.  Phylogeographic analysis of the corn snake (Elaphe guttata) complex as inferred from maximum likelihood and Bayesian analyses.  Molecular Phylogenetics and Evolution 25 (2002): 465-476.

Rattlesnake eats Red-winged Blackbird

Houston birder Mark Bartosik captured a stunning series of images of a Western Diamondback Rattlesnake (Crotalus atrox) downing a Red-winged Blackbird that it had killed near a birding trail in the Quintana Park near Freeport.  According to Bartosik, the entire incident was observed by about a dozen birders, whose presence apparently failed to distract the snake from his repast.  Remarkably, the snake was seemingly left unmolested (birders tend to get rather anthropomorphic when their favorite animals are harmed by other life forms). 

http://www.pbase.com/mbb/image/111817088

The image linked is the first in a series.  Use the "next" button to view the rest. 

One has to wonder if the birders who congregate in the Freeport area are aware that it - along with most of the central and lower Texas Gulf Coast - sports one of the densest populations of truly large venomous snakes to be found anywhere. 

Jack Reid – In Memoriam

Jack in his Kelly AFB Civilian Guard uniform with a Western Diamondback Rattlesnake (Crotalus atrox).
(U.S. Air Force photo circa 1959.)

Most readers of this site will not recognize the name of Jack R. Reid, but if you were an aspiring young herpetologist in the 1950’s and 1960’s in the San Antonio area it is likely that Jack served as your mentor at some point along the way.

 

I am not sure exactly when Jack became fascinated with reptiles and amphibians, but shortly after World War II he was himself mentored by the noted herpetologist John Werler, who was then curator of reptiles at the San Antonio Zoological Gardens.  Although never officially employed by the zoo, Jack was prominent among an entourage of young men who basically served as Werler’s interns, many of whom went on to careers in zoology and higher education themselves.

 

Since Werler’s research interests centered on the herpetology of Texas and the sparsely-explored portions of southern Mexico, it was natural that Jack became part of many expeditions mounted by Werler into those regions.  His verbal accounts of those trips were legendary and highly entertaining.  On such a trip to the isolated Sierra de los Tuxtlas range in southern Vera Cruz, on February 15, 1953, Jack was climbing one of the many epiphytic-laden trees on the rim of the extinct Volcan San Martin when he encountered and collected an unfamiliar greenish lizard that he thought resembled an alligator lizard.  Not quite a year later he and Werler managed to find another specimen of the puzzling lizard.  In 1961 Werler and Frederick A. Shannon officially designated the new lizard species as Abronia reidi, in Jack’s honor as its discoverer (Werler and Shannon, 1961).  Werler and Shannon, as was customary at the time, did not assign a common name to the new lizard, but Ernest Liner later suggested that the highly endemic form be known as Reid’s Arboreal Alligator Lizard (Liner, 1984).  Although this was the only species to be named in his honor, Jack was instrumental in many of the other herpetological discoveries made by those expeditions. 

 

Jack looking for herps among epiphytic bromeliads in Vera Cruz, Mexico.
(Donald M. Darling photo, circa 1954)

Jack holding a Don Darling and/or John Werler photo of Abronia reidi.  The map he is pointing to does not extend far enough south to include the collecting locality for the lizard. 
(U.S. Army photo, circa 1954).

In the late 1950’s, after John Werler had departed San Antonio to assume similar responsibilities at the Houston Zoo, Jack teamed up with R. Earl Olson and several others to initiate the Southwest Texas Herpetological Society, which was supported by the Witte Memorial Museum, where Olson eventually became curator of natural history.  Although this society was as notoriously short-lived as most of its ilk, it did have the ambitious goal of regularly publishing a mimeographed bulletin incorporating herpetological research and opinion from the area.  Jack, Olson, and Al Dinkins, the San Antonio Zoo’s new reptile curator, predictably authored most of the articles appearing in the “Bulletin”.