Data from: Divergence in brain composition during the early stages of ecological specialization in Heliconius butterflies

During speciation across ecological gradients diverging populations are
exposed to contrasting sensory and spatial information that present new
behavioural and perceptive challenges. These challenges may be met by
heritable or environmentally-induced changes in brain function which
mediate behaviour. However, few studies have investigated patterns of
neural divergence at the early stages of speciation, inhibiting our
understanding of the relative importance of these processes. Here, we
provide a novel case study. The incipient species pair, Heliconius erato
and H. himera are parapatric across an environmental and altitudinal
gradient. Despite ongoing gene flow, these species have divergent
ecological, behavioural and physiological traits. We demonstrate that
these taxa also differ significantly in brain composition, in particular
in the relative levels of investment in structures that process sensory
information. These differences are not explained solely by
environmentally-induced plasticity, but reflect heritable, non-allometric
shifts in brain structure. We suggest these differences reflect divergence
to meet the demands of contrasting sensory ecologies. This conclusion
would support the hypothesis that the evolution of brain structure and
function play an important role in facilitating the emergence of
ecologically distinct species.