Abstract

Superfetation, the ability of a female to fertilize and carry simultaneous broods of embryos, has been documented in a variety of organisms, but most notably in the live-bearing fish, Poeciliidae. Current hypotheses for the evolution of superfetation include that superfetation evolved in response to morphological constraints on female body shape, and that superfetation may have evolved in response to resource availability. Further, there is increasing evidence that superfetation may be derived from matrotrophy, where at least some of the embryonic nourishment is supplied maternally, rather than by a yolk. Previous authors have developed analytical models that describe the conditions under which matrotrophy is favored over lecithotrophy (nourishment entirely from yolk) by manipulating resource availability. Similarly, this paper investigates the conditions that favor superfetation over non-superfetation by manipulating mean resource availability and variance in a state-dependent life history model. An increase in mean available resources decreased the gestational age at which individual offspring were born, but was not shown to affect the size of individuals at birth. Increasing variance resulted in an increased range of offspring sizes. An increase in mean resource availability resulted in an increase in total offspring born during the reproductive season. Increasing mean resources and variance had no effect on the number of offspring a female would birth at one time, but the number of gestating offspring was greater with high mean resource availability. Superfetation was not observed in any of the forward simulated females, regardless of the mean resource and variance.

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