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... These variations have been related to phylogeny, ontogeny, gender, diet and geographical snake location (Daltry et al., 1996;Barlow et al., 2009;Morgenstern and King et al., 2013;Kopper et al., 2015). Differences in these conditions can act as selective evolutionary pressures that, when involving populations of the same species, could also lead to variations in other phenotypic traits, such as body coloration (Brodie, 1992;Smyers et al., 2014). In this sense, morphological differences could be indicative of variations in the proportions of venom components and, consequently, in venom toxicity. ...
... These variations have been related to phylogeny, ontogeny, gender, diet and geographical snake location (Daltry et al., 1996;Barlow et al., 2009;Morgenstern and King et al., 2013;Kopper et al., 2015). Differences in these conditions can act as selective evolutionary pressures that, when involving populations of the same species, could also lead to variations in other phenotypic traits, such as body coloration (Brodie, 1992;Smyers et al., 2014). In this sense, morphological differences could be indicative of variations in the proportions of venom components and, consequently, in venom toxicity. ...
After a snakebite accident, species identification is of vital importance. However, the existence of intraspecific differences in the body coloration patterns of venomous snakes can generate confusion and delay a convenient and effective treatment. This is the situation for Porthidium lansbergii lansbergii from Colombia, for which two distinctive color morphs occur, and the relationship of these morphs with venom toxicity is unknown. Therefore, venom samples from specimens of these two morphs were collected from the Colombian Caribbean region, and their protein profiles compared. Likewise, their venom functional activities were evaluated in vitro and in vivo in BALB/C mice. Additionally, using sequences of the mitochondrial cytochrome b (Cyt-b) gene, the relationship between these Colombian P. lansbergii lansbergii morphotypes was investigated, and their phylogenetic positions were determined for the first time using Bayesian inference. Despite the noticeable coloration divergence between the individuals analyzed, similar protein profiles of their venoms were observed. Additionally, neither their lethality nor biochemical activities were notably different. In general, both venoms were highly proteolytic, lacked a coagulant effect in vitro, and extended the clotting time due to the action of venom components, such as disintegrins and proteases, that induce defibrination. These results agreed with the result of our phylogenetic analysis, suggesting that the two chromatic morphs do not represent isolated populations. The phylogenetic analyses also supported the currently recognized P. lansbergii lansbergii subspecies as a monophyletic complex. In conclusion, the results of this investigation suggest similar clinical manifestations regardless of body coloration after a P. lansbergii lansbergii envenomation, and pools can therefore be used for antivenom development, medical treatments, and further research efforts.
Both color (i.e., reflectance) and body size should influence body temperature in heliothermic ectotherms. We compared heating rates and equilibrium temperatures between the normal striped morph and the solid black melanistic morph of the garter snake, Thamnophis sirtalis, from polymorphic populations in the Lake Erie region. Snakes ranging in mass from 2.6–216.2 g were divided into three size classes (small, medium, and large). Using temperature-sensitive PIT tags, we tested pairs of snakes under artificial light in an environmental chamber, then used curvilinear regressions to estimate heating rate and equilibrium temperature. In small and medium-sized snakes, we found no difference in heating rate nor equilibrium temperature between morphs, suggesting that melanism does not provide a thermal advantage in young snakes. In large snakes, morph affected equilibrium temperature, but not heating rate. Melanistics averaged 1.3 C warmer than striped snakes. This difference may represent a thermal advantage for adults, of which gravid females are the largest and may have the most to gain from a thermal advantage.
Populations of the garter snake in the Lake Erie area consist of striped and melanistic morphs. The frequently of melanistic morphs is similar between sexes but varies greatly among 7 island and 15 mainland sites: from 0.00-0.59. Thermoregulatory differences thought to exist between morphs have not resulted in differences between morphs in frequency of reproduction by adult females or in snout-vent length of adults of either sex. Non-selective factors (genetic drift, founder effect) may influence morph frequencies but have not produced significantly greater variance in morph frequency among island sites than among mainland sites. -Author
The Maritime Garter Snake, Thamnophis sirtalis pallidulus, is highly variable in pattern and colour. Although this subspecies is largely defined on the basis of colour, four colour morphs have previously been described for the subspecies, including a melanistic form. Based on specimens from Nova Scotia, Canada, a fifth, uncommon erythristic variant is added to the complex colour variation known for the Maritime Garter Snake.
We studied geographic variation in reproductive characteristics, especially litter size and neonate size, among several populations across Canada of the wide-ranging garter snake, Thamnophis sirtalis. Gravid females differed significantly in body size among sites. However, even after we corrected for intersite differences in maternal body size, there were highly significant differences among populations in litter size and neonate size. Populations with large litters tended to have small progeny, but we found only weak evidence of a "tradeoff" between neonate size and litter size within populations. There was a conspicuous east-west difference in reproductive characteristics of snakes: snakes from eastern Canada were relatively small at maturity and produced large litters of very small young, whereas those from western Canada generally were large and produced smaller litters (for a given body size) of larger young. Although litter size and neonate size are both phenotypically plastic traits, the differences observed among populations in this study were often much larger than those expected from simple environmental influences. We, therefore, hypothesize that reproductive traits differ genetically among populations of T. sirtalis, at least between eastern and western Canada.
Morphological variation in 14 head dimensions of 333 eastern garter snakes from four islands of the Beaver archipelago and adjacent Waugoshance Point, Michigan, was analyzed by multivariate statistical methods. Five principal component axes explained 62.8% of the variation in the data set. Statistically significant (P < 0.05) differences in head shape were found both among island populations and between islands and the mainland. Based on Mantel tests, the structure of the morphological variation was concordant neither with the history of geological events following the last glacial retreat nor with the genetic population structure derived from allozyme data. We suggest that natural selection based on prey availability may have effected the observed variation among these snake populations.
We report on the remarkable variation and frequency of color morphs within and among eight populations of the Common Gartersnake (Thamnophis sirtalis) in central Manitoba, Canada and one on Isle Royale, Michigan, USA. Five color morph categories are identified, one melanistic and four scored on a qualitative scale based on expression of red pigment. In the most northern population (Jenpeg, 54.464 degrees N, 98.115 degrees W) and two island populations (George Island, Lake Winnipeg, 52.819 degrees N, 97.620 degrees W; Isle Royale, 48.102 degrees N, 88.601 degrees W), all five color morphs were expressed. The northernmost population also exhibited sexual color dimorphism, with female snakes expressing significantly more red than males. In contrast, two central and western populations showed very little variation, with only two of the most similar color morphs present. We provide the first report of erythristic snakes in Manitoba, found in three separate locations around Lake Winnipeg. Melanistic snakes are also reported from three new localities in the province, all widely disjunct from previously identified sites around Lake Winnipegosis. Manitoban and isle Royale populations are compared with color frequency data from sites in mainland Michigan and in Kansas. Color patterns among populations do not follow traditionally recognized zones of intergradation between T. s. parietal's and T. s. sirtalis. The extreme intrapopulational variation suggests that subspecies of T. sirtalis based on color are of questionable validity.
The results of 11 captive matings among nine female and six male descendents of six wild-caught female common garter snakes from polymorphic populations near Lake Erie confirm that melanism is inherited as a simple Mendelian trait and is recessive to a striped pattern. The make-up of litters born to 71 wild-caught females from five sites corroborate this result: striped females never produced all melanistic litters and the frequency of entirely striped, mixed, and entirely melanistic litters conforms to expectations based on estimated allele frequencies. Possible explanations for a previously reported nou-Mendelian inheritance of melanism include the occurrence of a somatic mutation or bias in sperm production and fertilization ability.