Differential Susceptibility of Sympatric Garter Snake Species to Amphibian Skin Secretions

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Abstract
On Vancouver Island [Canada], the garter snake Thamnophis sirtalis preys heavily on amphibians while 2 sympatric garter snake species do not. One possible explanation is that the species have different preferences for such prey and/or that they are differentially susceptible to noxious or toxic amphibian skin secretions. These ideas were examined in this study. Relative prey preferences (in terms of tongue flicks) did not differ significantly among naive young of the 3 spp. T. elegans and T. sirtalis, however, showed overall higher tongue-flick responses than T. ordinoides to amphibian extracts. Also, T. sirtalis and T. elegans ate more amphibians in feeding experiments than T. ordinoides, Neither T. elegans or T. ordinoides suffered any apparent ill effects when forced-fed whole Rana aurora, Bufo boreas and Hyla regilla, but both suffered apparent loss of motor function when force-fed whole Taricha granulosa. In general, Thamnophis sirtalis readily ate all amphibian species offered without any apparent ill effects and, when forced-fed Taricha granulosa, a majority of snakes were unaffected by tarichatoxin. It appears that Taricha, while not lethal, may be sufficiently debilitating that it is avoided by Thamnophis elegans and T. ordinoides. Differential susceptibility to toxins in general, however, does not seem to explain the differential consumption of amphibians by these 3 spp. on Vancouver Island.

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