Data from: The costs of a big brain: extreme encephalization results in higher energetic demand and reduced hypoxia tolerance in weakly electric African fishes

A large brain can offer several cognitive advantages. However, brain
tissue has an especially high metabolic rate. Thus, evolving an enlarged
brain requires either a decrease in other energetic requirements, or an
increase in overall energy consumption. Previous studies have found
conflicting evidence for these hypotheses, leaving the metabolic costs and
constraints in the evolution of increased encephalization unclear.
Mormyrid electric fishes have extreme encephalization comparable to that
of primates. Here, we show that brain size varies widely among mormyrid
species, and that there is little evidence for a trade-off with organ
size, but instead a correlation between brain size and resting oxygen
consumption rate. Additionally, we show that increased brain size
correlates with decreased hypoxia tolerance. Our data thus provide a
non-mammalian example of extreme encephalization that is accommodated by
an increase in overall energy consumption. Previous studies have found
energetic trade-offs with variation in brain size in taxa that have not
experienced extreme encephalization comparable with that of primates and
mormyrids. Therefore, we suggest that energetic trade-offs can only
explain the evolution of moderate increases in brain size, and that the
energetic requirements of extreme encephalization may necessitate
increased overall energy investment.