Month: January 2025

Latest “buzz” about nesting choices poses a sunny conundrum for bees

/ gtattersall

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.

Close-up image of Ceratina calcarata (photo by Jessie deHaan).

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!

Unlocking the Motivations of Repetitive Behaviours in Reptiles

/ gtattersall

Our latest study (https://doi.org/10.1016/j.applanim.2024.106484) sheds light on a perplexing behaviour seen in captive reptiles, namely their interactions with barriers (IWB), a form of repetitive behaviour akin to pacing in mammals. As part of her PhD research, Melanie Denommé investigated the motivations behind IWB in bearded dragons (Pogona vitticeps; Figure 1) over a three year period, and formally tested whether it stems from a “desire” to escape their enclosures.

Figure 1. Photo of a bearded dragon interacting with a barrier (called glass surfing sometimes if the lizard moves back and forth across the transparent barrier, although reptiles may do this on non-transparent barriers as well).

Our findings revealed a strong preference for performing IWB near the front barrier of their environment (Figure 2), the only known escape route; even when half of it was obscured; they also direct more of their behaviour toward the transparent part of the front barrier. Interestingly, IWB was 15 times more likely to occur around the time when lizards defecated, supporting an argument that these behaviours may be driven by escape-related motivations, at least with respect the need to find suitable defecation areas.  However, no clear link was found between IWB and anticipation of feeding, suggesting species-specific differences in how repetitive behaviours are triggered. Despite these results, lizards would still exhibit IWB with non-transparent barriers (Figure 2), suggesting that escape is not the exclusive explanation for these repetitive behaviours.

Figure 2. Results from multiple rounds of home cage observations of barrier wall interaction (minutes per day). Bearded dragons interacted more with the front barrier (that is, the barrier from which escape could occur), although still exhibited IWB (interacting with barriers) along the other 3 walls of the enclosure.

Seasonal and sex-related patterns offered further nuance. Contrary to expectations, female lizards performed IWB more during spring, while males showed consistent levels year-round. This might reflect frustrated breeding-season motivations, as females in the wild often roam widely in search of mates, a behaviour restricted in captivity. These findings emphasize the complex interplay between natural instincts and captive conditions, highlighting the importance of tailoring environments to better meet the needs of individual animals. By understanding these behaviours and using an evidence-based approach, we can deepen insights into the diverse causes of repetitive behaviours across species and thereby improve captive reptile welfare.

Note that the actual levels of IWB seen were low throughout the study, with numerous animals never performing the behaviour. There appear to be individual differences in the expression of IWB.

Citation

Denommé, M and Tattersall, GJ. 2025. Investigating the motivations of repetitive barrier interactions in Pogona vitticeps. Applied Animal Behaviour Science, 283: 106484. https://doi.org/10.1016/j.applanim.2024.106484