Variable flight distance to resources results in changing sex allocation decisions, Megachile rotundata

Abstract

Resource availability and location are expected to vary, based on use by individuals and changing ecological conditions; the response of animals to those changes is critical to their fitness. To investigate the effects of changing conditions on fitness, we conducted field experiments using the central-place-foraging alfalfa leafcutting bee (Megachile rotundata), examining the changes in sex allocation when presented with changes in flight distance required to obtain resources. The results suggest that changes in flight distance to resources during the year’s flight season altered subsequent allocation decisions: mothers experiencing long flight distance to resources early in the season and short flight distance later in the season generated a greater proportion of female offspring than mothers experiencing the opposite. During the second half of the season, however, it was current experimental conditions significantly impacting decisions with those mothers residing near the resources producing a greater portion of female offspring than those far from resources, regardless of flight distances experienced earlier in the year. These results show that sex allocation decisions may change dynamically during a female’s lifetime in response to ecological changes. We also looked at these results through the contradicting hypotheses marginal value theorem and sex ratio theory, finding that the latter may be in play depending on an individual’s past and/or present condition.