Copulating with multiple mates enhances female fecundity but not egg-to-adult survival in the bruchid beetle Callosobruchus maculatus.

Postcopulatory sexual selection theory has come a long way since the evolutionary implications of sperm competition were first spelled out by Parker (1970). However, one of the most enduring questions remains: why do females copulate with multiple males? Here we show that females copulating with multiple males lay more eggs than those copulating repeatedly with the same male. We also show egg-to-adult survival to be more variable when females copulate multiply with different males and less variable when they copulate multiply with the same male. This supports the notion that egg-to-adult survival may depend on the genetic compatibility of males and females. However, pre-adult survival was highest when females copulated repeatedly with the same male rather than with different males. Thus, it would appear that polyandry in this species does not function to reduce the risk of embryo failure resulting from fertilization by genetically incompatible sperm.