Sex Allocation in a Solitary Bee: A Behavioural Ecology Approach

Organisms reproducing sexually face the question of how to allocate investment to offspring between the sexes. My research objective was to evaluate the impact of ecological factors on maternal allocation decisions related to size, sex and number of offspring produced. Empirical and theoretical work was carried out using the alfalfa leafcutter bee, Megachile rotundata. Decreased resource levels resulted in lower maternal investment per daughter and fewer offspring produced; investment per son and sex ratio were unaffected. Increased flight distance required to obtain resources resulted in decreased investment per individual daughter and son, overall production of offspring and proportion of daughters produced. Using a dynamic state variable model to determine optimal maternal investment, I found optimal offspring size was controlled by the shape of maternal fitness return curves while sex ratio was influenced by numerous ecological factors. In conclusion, ecological factors appear to be important determinants of maternal investment in offspring.