Oviposition dynamics and sex ratio model assumptions in pollinating fig wasps

Abstract

This thesis investigates a few assumptions of sex allocation in fig wasps, a pivotal subject in evolutionary biology and sex ratio theory. We investigate specifically if species can be considered in isolation of one another, and if the females that share a fig, oviposit simultaneously or sequentially. In doing so the study tries to explain deviations in fig wasp sex ratios from predictions made by classical frequency-dependent selection models. As more mothers oviposit in a fig, their offspring sex ratios become less female biased as predicted, but to a lesser degree than is optimal. The adaptive adjustment is a result of the two mechanisms of sex ratio adjustment in pollinating fig wasps: a passive response due to unlaid female eggs in competitive environments, and a facultative response involving increased male egg production in the presence of co-foundresses. An information-theoretic approach allowed me to contrast different hypotheses and to conclude that the presence of heterospecifics disrupts these mechanisms, leading to maladaptive sex ratios and illustrating trade-offs between versatility and specialization. The standard sex ratio models based on local mate competition theory assumes that females oviposit simultaneous. My direct observations show that sequential oviposition is in fact more frequent than simultaneous oviposition and this can help to explain sex ratios that are too female-biased in multi-mother figs. To investigate sequentiality further, I used an Approximate Bayesian Computation approach to estimate parameters such as wasp entry probabilities, foundress longevity, and ostiole closure timing The estimated parameters suggests that sequential oviposition is very likely because figs stay open for longer than wasps stay alive.