Brain size predicts bees’ tolerance to urban environments

The rapid conversion of natural habitats to anthropogenic landscapes is
threatening insect pollinators worldwide, raising concern on the negative
consequences for their fundamental role as plant pollinators. However, not
all pollinators are negatively affected by habitat conversion, as certain
species find in anthropogenic landscapes appropriate resources to persist
and proliferate. The reason why some species thrive in anthropogenic
environments while most find them inhospitable remains poorly understood.
The cognitive buffer hypothesis, widely supported in vertebrates but
untested in insects, offers a potential explanation. This theory suggests
that species with larger brains have enhanced behavioural plasticity,
enabling them to confront and adapt to novel challenges. To investigate
this hypothesis in insects, we measured brains for 89 bee species, and
evaluated the association between brain size and habitat preferences. Our
analyses revealed that bee species that prefer urban habitats had larger
brains relative to their body size than those who prefer forested or
agricultural habitats. Additionally, urban bees exhibited larger body
sizes and, consequently, larger absolute brain sizes. Our results provide
the first empirical support for the cognitive buffer hypothesis in
invertebrates, suggesting that a large brain in bees could confer
behavioural advantages to tolerate urban environments.