Optimal Egg Size Theory : Does Predation by Fish Affect Egg Size in Ambystoma maculatum?

  • Cunnington D
  • Brooks R
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Abstract

.-Amphibialanr vaeh atching from largere ggs may be better equipped to avoid predationt han larvae hatching from smaller eggs. We use the context of optimal egg size theory to investigate Ambystoma maculatum egg size in lakes with and without fish. Optimal egg size theory predicts that organisms produce an egg size which balances the fitness advantage of producing large eggs against the fitness cost of producing few eggs. Consequently if offspring fitness is relatively lower at a given egg size in one environment than another, the optimal egg size should be relatively larger in the harsher environment. We investigated this prediction at eight permanent lakes in Algonquin Park, Ontario. We analyzed differences in egg size with a three-level nested analysis of variance at the levels of treatment (lakes with and without fish), lake, and clutch. We found no significant difference in treatment means, and, therefore, the hypothesis was not supported. There was no significant variance component due to lake of origin, but there was a highly significant variancec omponenta ttributedt o the clutch,a nd thereforef, emale effect This variationi s presumablyc aused primarily by differences in female body size, and its adaptive significance, if any, is unclear. We reasoned 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 evolve large differences in egg size.

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Authors

  • David C Cunnington

  • Ronald J Brooks

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