Maternal allocation decisions impacted by variable ecological conditions in a solitary bee: behavioural ecology perspectives

Parents can invest in offspring through a variety of behaviours. I use a combination of theoretical and empirical studies to examine how resource and sex allocation decisions toward offspring were altered in response to changing ecological conditions. My empirical work was done using the haplodiploid alfalfa leafcutter bee (Megachile rotundata), where sex of offspring can be controlled and mothers do all offspring provisioning. My theoretical research demonstrated no single factor determining sex allocation; instead, there is some ‘optimal balance’ between factors. Empirical work results suggest a similar situation. All three experiments demonstrated different factors that impacted sex allocation decisions: flight distance to resources, resource levels, and local population density. Longer flight distances resulted in fewer offspring produced throughout the season, but a greater proportion of daughters produced in the first half of the season and a lower proportion of daughters in the second half of the season compared to mothers with short distance to resources. Lower resource-level treatments had similar effects during the first half of the season as with long flight distance; however, during the second half mothers continued to produce a greater proportion of daughters under low resource conditions compared to high. Lower local population density resulted in both a greater proportion of daughters being produced as well as a greater number of offspring per individual nest compared with high-density conditions. We also addressed two other allocation decisions. We used flight distance to address the question of what foraging currency mothers maximize when collecting resources for offspring. We found mothers increased load size with increased flight distance, suggesting that they are behaving in a manner that maximizes efficiency as opposed to net rate of energy intake. In regards to nest defence, mothers slightly increased nest defense as the nest size increased. However, unlike traditionally studied organisms, this increase in defense continued more steeply until the nest was basically completed and sealed, after which defense dropped suddenly. In combination, these studies contribute to our basic understanding of offspring allocation decisions in solitary organisms.