MHC class I and II genes in Serpentes

Genes of the major class I and II histocompatibility complex have been extensively studied in mammals. Studies of these antigens in reptiles are very scarce. Here we describe the characteristics of these genes in the suborder Serpentes. We identified the presence of a much larger number of molecules of class I and beta chains of class II than found in mammals. Snakes only have one gene for the class II alpha chain. In these species, class I genes can be classified into two types. Approximately half of the genes lack 10 amino acids in the α1 domain, producing a structural alteration in the interaction region with the T lymphocyte receptor. In the genome of Thamnophis elegans, two haplotypes of an individual were studied revealing a different number and location of class I genes between these haplotypes. The results indicate that in these species, the diversity in the MHC is generated by the presence or absence of genes, independent of the presence of alleles.

Factors affecting litter size in Western Gartersnake (Thamnophis elegans) in British Columbia: place, time, and size of mother

Life-history traits of organisms are influenced by both genetic and environmental factors. We used counts of offspring in captive-born litters to determine how geographic location, year-to-year variation, and body size of mother affected litter size of Western Gartersnake (Thamnophis elegans) in four widely separated populations in British Columbia. Litter size varied significantly among populations, but that variation was largely explained by differences in maternal body size among populations; that is, larger females had larger litters. With maternal size treated as a covariate, there was no further significant effect of location or of different years within sites on litter size. The overall regression, pooled over sites and years, between litter size and size of mother accounted for 55% of the total variation in litter size. Nonetheless, the significant variation in body size among locations calls for explanation and the consequent differences in litter size could be important demographically. Presumably, the large amount of unexplained residual variation reflects other differences, beyond body size, between individual mothers. Such differences among individuals might be determined by genetics or by environmental effects such as foraging success, but our data cannot address this question.

EFFECTS OF SEX, ENVIRONMENT, AND CONDITION ON THE MUSKING BEHAVIOR OF SYMPATRIC GARTERSNAKES (THAMNOPHIS SPP.)

Despite an abundance of studies documenting antipredator and defensive behaviors of gartersnakes (genus Thamnophis), few have quantitatively examined musking, a widely utilized antipredator tactic. In this study we quantify musking behaviors in the Terrestrial Gartersnake (Thamnophis elegans) and the Plains Gartersnake (T. radix) when hand-captured at four sites in and near Denver, Colorado, USA. Overall, Plains Gartersnakes musked significantly more often than Terrestrial Gartersnakes. Female Terrestrial Gartersnakes musked more frequently than males, a pattern not evident in the Plains Gartersnake. Additionally, we observed a positive correlation in body condition and musking propensity in Terrestrial Gartersnakes, suggesting resource-dependent behavior in this species. Musking behavior was consistent across variations in predation pressure, environmental conditions, and snake body size, all factors shown to influence other gartersnake defensive behaviors. These results corroborate other research which demonstrates that snake antipredator behaviors are determined by complex interactions of abiotic and biotic factors.

Gene expression of components of the insulin/insulin-like signaling pathway in response to heat stress in the garter snake, Thamnophis elegans

The insulin/insulin-like signaling (IIS) pathway is an evolutionary conserved molecular signaling pathway that regulates growth, reproduction, stress resistance, and longevity in response to nutrition and external stress. While the constituents of this pathway and their functions are relatively well understood in laboratory model animals, they have not been explored in many other organisms, with notable exceptions in the fisheries literature. We tested for the gene expression of four key components of this pathway in the garter snake (Thamnophis elegans) liver, and determine how the transcription of these components responds to heat stress. We found that the two insulin-like growth factor ligands (IGF-1 and IGF-2) and the receptors (IGF-1 Receptor and M6P/IGF-2 Receptor, or IGF-1R and IGF-2R) are expressed in garter snake liver tissue. Under normal laboratory conditions, IGF-2 and IGF-2R are expressed at a higher level than IGF-1 and IGF-1R. In response to heat stress, IGF-1 expression remained the same, IGF-2 expression decreased, and the expression of both receptors increased. These results demonstrate that elements of the IIS pathway are responsive to heat stress in snakes. Further studies are needed to fully understand the biological consequences of this response.