No sex differences in learning in wild bumblebees

Females and males often face different sources of selection, resulting in
dimorphism in morphological, physiological, and even cognitive traits. Sex
differences are often studied in respect to spatial cognition, yet the
different ecological roles of males and females might shape cognition in
multiple ways. For example, in dietary generalist bumblebees (Bombus), the
ability to learn associations is critical to female workers, who face
informationally-rich foraging scenarios as they collect nectar and pollen
from thousands of flowers over a period of weeks to months to feed the
colony. While male bumblebees likely need to learn associations as well,
they only forage for themselves while searching for potential mates. It is
thus less clear whether foraging males would benefit from the same
associative learning performance as foraging females. In this system, as
in others, cognitive performance is typically studied in lab-reared
animals under captive conditions, which may not be representative of
patterns in the wild. In the first test of sex and species differences in
cognition using wild bumblebees, we compared the performance of Bombus
vancouverensis nearcticus (formerly bifarius) and Bombus vosnesenskii of
both sexes on an associative learning task at Sierra Nevada (CA, USA)
field sites. Across both species, we found that males and females did not
differ in their ability to learn, although males were slower to respond to
the sucrose reward. These results offer the first evidence from natural
populations that male bumblebees may be equally as able to learn
associations as females, supporting findings from captive colonies of
commercial bees. The observed interspecific variation in learning ability
opens the door to using the Bombus system to test hypotheses about
comparative cognition.