Abstract:
To elucidate factors underlying the evolution of large brains in cetaceans, we examined 16 brains
from 14 cetartiodactyl species, with immunohistochemical techniques, for evidence of non-shivering
thermogenesis. We show that, in comparison to the 11 artiodactyl brains studied (from 11 species),
the 5 cetacean brains (from 3 species), exhibit an expanded expression of uncoupling protein 1
(UCP1, UCPs being mitochondrial inner membrane proteins that dissipate the proton gradient to
generate heat) in cortical neurons, immunolocalization of UCP4 within a substantial proportion of
glia throughout the brain, and an increased density of noradrenergic axonal boutons (noradrenaline
functioning to control concentrations of and activate UCPs). Thus, cetacean brains studied possess
multiple characteristics indicative of intensified thermogenetic functionality that can be related to
their current and historical obligatory aquatic niche. These findings necessitate reassessment of
our concepts regarding the reasons for large brain evolution and associated functional capacities in
cetaceans.
