BRITT, E.J.; HICKS, J.W.; BENNETT, A.F.; Univ. of California, Irvine; Univ. of California, Irvine; Univ. of California, Irvine: Production efficiency in prey specialist and generalist populations of Thamnophis elegans.
The Western Terrestrial Garter snake, T. elegans, exists in two geographically isolated populations in northern California: a coastal population with a specialized diet of slugs and an inland population with a generalized diet of fish, anurans, mice and leeches. Since some species of natricine snakes are obligate slug specialists, the intraspecific variation in T. elegans presents a unique opportunity to study digestion of different prey types in two diverse populations of conspecifics with different niches and selective pressures. Neonates of both populations demonstrate a high chemoreceptive response to a generalist fish prey diet whereas only the slug specialists have a chemoreceptive response to slug prey. The difference in chemoreception between the two populations translates into geographic variation in a behaviorally mediated response that governs prey detection and consumption. The inland snake populations have a high frequency of slug-refusing morphs, in which animals will refuse to ingest slugs. We hypothesized that the coastal population has a higher production efficiency on a slug diet than does the inland population, and that the two populations has an equal efficiency on fish prey. To test this, we measured production efficiency of each snake population on both prey types upon digestion of the meal. By standardizing the meal and determining its caloric content, the amount of energy remaining in the feces gave an estimate of total assimilation energy. The assimilation energy minus the cost of respiration resulted in an estimate of the production energy available for growth, storage and activity. Thus, the pattern in production efficiency was predicted to follow that of chemoreception and dietary habits, providing a possible link between feeding behavior and digestive physiology. Supported by NSF IBN-0091308 awarded to A.F. Bennett and J.W. Hicks.
