Aspects of Cannibalistic Morphs in a Population of Ambystoma t. tigrinum Larvae

Abstract

We report growth, body size and diet of typical and cannibalistic larval Ambystoma tigrinum morphs. The study population, located in northwestern Iowa (430 23' N, 950 1 1' W), currently represents the first instance of larval cannibalistic morphs in the subspecies A. t. tigrinum and the northeastern limit of cannibalistic morphs in the A. tigrinum complex. A comparison of food habits of typical larvae in 1980, when the cannibalistic morph was absent, with 1981, when the morph was present, shows no basic differences. In both years a wide variety of prey were ingested with Daphnia being most abundant. Because 1981 was a drought year and our study ponds were drying, our data support Collins and Cheek's (1983) work showing that density, not food, affects the expression of cannibalistic morph traits. Cannibalistic morphs grew much faster than typical larvae. If metamorphosis is size-dependent, cannibalistic morphs should have a higher survivorship under drying-marsh conditions.