The occurrence of sequential oviposition in fig wasps and the implications for interpreting sex ratio data

Abstract

Pollinating fig wasps are believed to adjust their sex ratios according to standard local mate competition (LMC) theory. Standard LMC theory assumes that all mothers ovipositing in a patch or fig does so simultaneously. However, it has been shown that fig wasps can oviposit sequentially. We counted the number of figs containing dead and living mothers in figs where mothers entered naturally to estimate the incidence of sequential and simultaneous oviposition. Single mothers were the norm in two wasp species, and multiple mothers the norm in the other two. However, contrary to LMC theory, in all four species, when multiple mothers occurred, sequential oviposition seems to occur more frequently than simultaneous oviposition. The sex allocation problem fig wasp mothers face is thus more complicated than the widely assumed simultaneous ovipositing situation, and it leads to several expectations. Single mother's sex ratios should increase as the probability of additional mothers increases. Naturally founded multi-mother figs should have more female-biased sex ratios than the standard LMC model predicts for the final number of mothers. This is because early-arriving mothers underestimate the number of mothers and lay more daughters than the final number of mothers would require and later-arriving mothers can lay fewer sons to be competitive against the first mothers' too female-biased clutches. Mothers must produce sex ratios that are optimised across a probabilistic range of foundress densities they experience.