Social and ecological drivers of life history evolution in wild bees

All organisms must balance energetic investment in essential functions, such as health and reproduction, and this typically leads to trade-offs over the course of a lifetime. However, these basic rules of life do not seem to apply to insects that live in social groups. For example, queens of some ants, bees, and termites can live for years or even decades, despite laying thousands or hundreds of thousands of eggs, but their sterile sisters and daughters live for just days or weeks.

The mechanisms underlying this drastic departure from otherwise universal life history trade-offs are unknown, in part due to limitations in the types of species that have been studied. This project will focus on wild bees to determine how variation in sociality influences how bees balance investment in reproduction, health, and longevity. By expanding the breadth (number of species) and depth (ecologically relevant experiments within a key species) of analysis, the project will provide unique insights into how bees optimize fitness under changing environmental conditions, which is critical for mitigating issues related to global food security in the face of pollinator decline.

The project will provide training and mentorship for students (undergraduate and graduate) and a postdoctoral researcher. Training will specifically target Native American students from a regional campus to broaden participation in STEM through mentorship in a summer research program and fellowship. Results generated from the research will be used to develop guided experiential learning modules in an upper division/graduate course called Genes and Behavior.

Life history theory has been a guidepost for interpreting variation in behavior and ecology through an evolutionary framework, but social insects seem to break the rules by escaping classic tradeoffs between fecundity and longevity. This suggests that social evolution influences life history evolution, fundamentally altering what seem to be otherwise basic constraints in how life history strategies can vary.

The team will investigate how wild bees invest in life history traits (immunity, reproduction) as a function of variation in the ecological and social environment in three sets of experiments. First, internal and external immunity will be assayed in multiple bee species to test alternative hypotheses for how the evolution of eusociality has shaped investment in immune function.

Second, the focus will shift to a facultatively eusocial bee (Megalopta genalis) that allows direct comparison of life history tradeoffs in solitary and social individuals under the same ecological conditions. Comparing immune response, oxidative stress, and gene expression profiles in three tissues between solitary and social females before and after offspring emergence will take advantage of natural differences in energy reserves to see how access to resources influences investment in survival (i.e., immunity, senescence, mortality risk) and reproduction, as well as the molecular pathways underpinning these traits.

A final set of experiments will test these findings directly by experimentally removing the workers from social M. genalis nests and measuring the effects on queen survival, reproduction, and their underlying mechanisms. These activities will identify the mechanisms by which social evolution influences life history evolution.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.