A molecular investigation of population structure and paternity in the common garter snake, thamnophis sirtalis
Date
1998
Authors
Garner, Trenton W.J.
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Abstract
The study of genetic variation within and among populations of a species is a cornerstone of evolutionary biology. Here, I use the wideranging species, Thamnophis sirtalis, to study genetic variation between two classes of study sites that are predicted to differ in genetic variation. I also test the role of multiple paternity in contributing to within population genetic variation in this species.
At salmon hatcheries on Vancouver Island, Common Garter Snakes often feed heavily on salmon smolts, which represent an abundant food source. The frequently high abundance of snakes at hatcheries thus may result either from snakes being attracted to them from surrounding areas or from explosion of a local population due to a rich source of food. If the former, genetic variation at hatcheries should be higher than at natural sites; if the latter, genetic variation should be similar to that of natural sites, or perhaps even lower. Microsatellite markers revealed little detectable genetic variation among sites, but genetic profiles from one locus suggest that hatcheries are not as stable as natural sites, providing slight support for the first hypothesis. Although genetic variation among populations was not closely related to geographic relationships , the data do suggest that snakes from southern Vancouver Island are distinct from more northern sites.
Based on single-locus microsatellite DNA analysis, there was clear evidence of multiple paternity in 37.5% of 16 litters born in the laboratory. However, the significance of this phenomenon is not clear. Snakes exhibiting multiple paternity were similar in body size and litter size to snakes showing only single paternity; they also did not differ in the size of their offspring or in the proportion of stillborn offspring they produced. Furthermore, there was no demonstrable difference in the frequency of multiple paternity between my sample and that from another study of eastern snakes, which produce much larger litters.