FEMALE CONTROL OF SPERM TRANSFER AND INTRASPECIFIC VARIATION IN SPERMPRECEDENCE - ANTECEDENTS TO THE EVOLUTION OF A COURTSHIP FOOD GIFT

Manipulation of ejaculates is believed to be an important avenue of fe male choice throughout the animal kingdom, but evidence of its importa nce to sexual selection remains scarce. In crickets, such manipulation is manifest in the premature removal of the externally attached sperm atophore, which may afford females an important means of postcopulator y mate choice. We tested the hypothesis that premature spermatophore r emoval contributes significantly to intraspecific variation in sperm p recedence by (1) experimentally manipulating spermatophore attachment durations of competing male Gryllodes sigillatus and (2) employing pro tein electrophoresis to determine the paternity of doubly mated female s. The relative spermatophore attachment durations of competing males had a significant influence on male paternity, but the pattern of sper m precedence deviated significantly from the predictions of an ideal l ottery. Instead, paternity data and morphological evidence accorded be st with a model of partial sperm displacement derived here. Our model is similar to a displacement model of Parker et al. in that sperm of t he second male mixes instantaneously with that of the first throughout the displacement process, but the novel feature of our model is that the number of sperm displaced is only a fraction of the number of sper m transferred by the second male. Regardless of the underlying mechani sm, female G. sigillatus can clearly alter the paternity of their offs pring through their spermatophore-removal behavior, and employ such cr yptic choice in favoring larger males and those providing larger court ship food gifts. We discuss how female control of sperm transfer and i ntraspecific variation in sperm precedence may be important precursors to the evolution of gift giving in insects.