Nest site selection is a critical decision for many animals, but for small carpenter bees (Ceratina calcarata), it’s a gamble with possibly far-reaching consequences. In our recent study, deHaan et al. explored the delicate balance between benefits and risks when mother bees choose to nest in sunny or shaded environments. The research uncovers an intriguing trade-off: while sunny nests boost maternal fitness by reducing the chances of complete brood failure, they come at the cost of smaller, thermally- stressed offspring. Thanks Mum!

Sunny nests, which are warmer, offer distinct advantages to mother bees. These nests enable earlier foraging activity and faster brood development, reducing the window of vulnerability to predators and parasites. To test this in an field experiment, however, we (i.e., Jessie deHaan) had to find nests early in the spring and relocate some nests to the shade and some to the sun to allow for these effects to be tested across the summer.  Sunny nests reached maximum temperatures that were up to 3.8 °C higher than the maximum temperatures reached in the shade;  further, the sunny nests would have been warmer for ~14-15 hours per day during the study period. In short, sunny nests are obviously warmer than shady nests, but also undergo wider diurnal changes in temperature.  

In our experiment, we found that 59% of sunny nests successfully produced offspring, compared to only 32% of shaded nests. However, these sunnier sites posed challenges for developing juveniles, who faced higher temperatures that necessitated energy-intensive thermoprotective measures. Juveniles from sunny nests were smaller and had elevated heat tolerance thresholds (CTmax), suggesting they diverted resources from growth to survival. Since mothers provision each brood cell with a fixed amount of pollen after laying their egg, the size the young bees reach must reflect the trade-off between temperature-dependent energy expenditure and development. This trade-off also highlights how maternal decisions prioritize their own fitness, sometimes at the expense of their offspring’s long-term prospects.

This research sheds light on the intricate dynamics of environmental stress, maternal investment, and juvenile development in ectotherms like bees. With climate change amplifying temperature extremes, understanding these relationships could be crucial for predicting the future of pollinator populations.

This paper was the result of Jessie deHaan’s MSc research in Dr. Miriam Richards lab (co-supervised in part in my lab), but conducted during the lockdown period during the COVID-19 travel and research restrictions.  At the time, faculty and student researchers were not permitted to come to campus, or initiate new research projects in the field (even though government scientists were allowed to carry on their research).  For an MSc student in the middle of their research project, 2020 presented challenges to which Jessie rapidly adapted by running their experiments in their own backyard and in the basement of their house, using a modified PCR machine as the bee incubator! Hats off to ingenuity in the face of adversity.  

Citation

deHaan, JL, Maretski, J, Skandalis, A, Tattersall, GJ, and Richards, MH. 2025. Costs and benefits of maternal nest choice: trade-offs between brood survival and thermal stress. Ecology. https://doi.org/10.1002/ecy.4525

See Dr. Miriam Richards lab page for more details about bees and her bee research!