Optimal egg size theory: Does predation by fish affect egg size in Ambystoma maculatum?

Amphibian larvae hatching ham larger eggs may be better equipped to avoid p redation than larvae hatching from smaller eggs. We use the context of opti mal egg size theory to investigate Ambystoma maculatum egg size in lakes wi th and without fish. Optimal egg size theory predicts that organisms produc e an egg size which balances the fitness advantage of producing large eggs against the fitness cost of producing few eggs. Consequently if offspring f itness is relatively lower at a given egg size in one environment than anot her, the optimal egg size should be relatively larger in the harsher enviro nment. We investigated this prediction at eight permanent lakes in Algonqui n Park, Ontario. We analyzed differences in egg size with a three-level nes ted analysis of variance at the levels of treatment (lakes with and without fish), lake, and clutch. We found no significant difference in treatment m eans, and, therefore, the hypothesis was not supported. There was no signif icant variance component due to lake of origin, but there was a highly sign ificant variance component attributed to the clutch and therefore, female e ffect This variation is presumably caused primarily by differences in femal e body size, and its adaptive significance, if any, is unclear. We masoned that the presence of fish has not caused females to adapted their egg size because (1) small differences in egg size may make little or no difference in larval survival, and (2) the populations are not isolated enough to evol ve large differences in egg size.