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

Abstract

Growth, body size and diet of typical and cannibalistic larval A. tigrinum morphs are reported. The study population, located in northwestern Iowa (43.degree. 23'' N, 95.degree. 11'' 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 the study ponds were drying, data support other studies 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.