Meeting Abstract
Trade-offs are a powerful tool in investigations of natural selection. Body size may be under intense selective pressure, especially in flying animals, because it offers absolute strength but reduces maneuverability. Eastern carpenter bees (Xylocopa virginica) are large, semi-solitary pollinators. They must be small and agile to hover, avoid predators, and defend their nests from conspecifics, yet large and strong to win in frequent intraspecific direct combat. To begin to investigate the effects of size in these bees, I measured performance during aggressive nest-defense flights in Charlottesville, VA, USA. I used three GoPro cameras (120 Hz), wand-calibrated and synchronized using Argus, to record over 1300 flight paths from the roughly 20 bees in the colony over two days. I developed a custom Python program using background subtraction and image recognition to automatically produce 3D tracks, which were manually refined. Large size is predicted to reduce hovering ability or peak acceleration. Median flight speed in non-interacting bees was 0.9 ms-1, meaning bees spent significant time at or near hovering. Maximum accelerations regularly exceeded 4g, and peaked over 10g, when bees were interacting. Compared to existing data on other species, these results suggest that any size-dependent penalty in flight performance may be too small to detect without more direct comparison. Further, some interactions preceding combat occurred at low speeds and accelerations indicating that maximal acceleration may not be a critical factor in such aggression. One potential conclusion is that the strength that comes with increased size outweighs the relatively small flight penalties in this species, and could be a driver behind the evolution of large size in this and other solitary pollinators.
