Many bee species are shifting their spring emergence phenologies in response to climate-warming. The interspecific effects of phenological shifts, such as phenological mismatches with flowering plants, have been widely studied in recent decades. However, the potential for intraspecific effects has received less attention. For example, less stored fat available for energy during winter diapause in male solitary bees compared to females may constrain male emergence plasticity. Thus, as environmental conditions during winter (i.e., temperature, duration, and annual variability) change, male emergence phenologies may become uncoupled from female phenologies. Reduced male-female phenological overlap may decrease mating success, reproductive success, and influence foraging behavior (i.e., unmated females may forage less when not provisioning a nest). To assess the effects of intraspecific male-female phenological mismatches in solitary bees, we manipulated the number of days between the emergence date of male and female Osmia lignaria bees by storing emerged males without food at 6°C between 1 and 22 days prior to female emergence. Males where then placed with female bees inside mesh-sided mesocosms containing flowering plants and nesting habitat for one month. We recorded flower visitation patterns and bee life span, and collected nests containing bee offspring at the end of the experiment.
Currently we are overwintering bee offspring collected from mesocosms to assess total reproductive success by recording the viable offspring that emerge during spring 2017. We expect reproductive success to decrease as days between male and female emergence increase due to decreasing male-female phenological overlap (i.e., opportunity to mate). Preliminary results comparing male bee life span after release into mesocosms suggests a 4% decrease in mean male survival over the duration of the experiment for each one day increase between male and female emergence, suggesting male-female phenological overlap is reduced as days between male and female emergence increase. If reduced phenological overlap translates to reduced mating success, we expect unmated females to forage less often. Preliminary results show that female foraging patterns (i.e., number of flowers visited and time spent visiting flowers) did not differ between treatments, suggesting either that unmated females forage at equal rates compared to mated females, or that reduced phenological overlap did not affect mating success. We are eager to see how reduced male-female phenological overlap affected total reproductive success among our treatments and hope our results help guide further research into the mechanisms by which phenological shifts affect solitary bee reproductive success and plant-pollinator communities.