The ecological and physiological consequences of sun vs. shade nesting for the small carpenter bee, Ceratina calcarata, and their offspring

Abstract

Ceratina calcarata mothers choose their nesting location and that choice can have developmental consequences for their offspring. Nests in the sun experience higher developmental temperatures, reducing self-feeding insect body size through a phenomenon called the Temperature-Size Rule. How does developmental temperature affect body size in insects whose mothers’ feed them; for example, in mass-provisioning bees where all the food an offspring needs to complete development is provided by the mother upfront? What are the physiological advantages or disadvantages conveyed to offspring in sunny nests? In this thesis I used C. calcarata to investigate the ecological and behavioural consequences of nest location choice (sun or shade) on mothers, as well as the physiological consequences of developmental temperature on their offspring. Nests randomly allocated to the shade treatment were more likely to be empty when opened, indicating that shaded nesting locations were not preferred. Mothers nesting in the sun foraged more often for nectar than shade mothers, but provisioned similar sized pollen masses. Sunny nests were hotter than shaded nests, even more so if they were oriented on an angle. Offspring from sunny nests were smaller than shade bees in agreement with the Temperature Size Rule. Sunny offspring also had higher thermal tolerance than offspring from the shade but less frequent DGE bursts at 25°C compared to shade bees, suggesting a lower metabolism at a moderate temperature. As a result, I conclude offspring from sunny nests displayed irreversible developmental thermal plasticity. Offspring from sunny nests experienced a thermal trade-off as a result of their developmental conditions; they had a capacity for higher thermal tolerance as evidenced by a shifted thermal breadth, but at the expense of a smaller adult body size. Such trade-offs may enhance their response to climate change and contribute to speciation.