Data from: Müllerian mimicry of a quantitative trait despite contrasting levels of genomic divergence and selection

Hybrid zones, where distinct populations meet and interbreed, give insight
into how differences between populations are maintained despite gene flow.
Studying clines in genetic loci and adaptive traits across hybrid zones is
a powerful method for understanding how selection drives differentiation
within a single species, but can also be used to compare parallel
divergence in different species responding to a common selective pressure.
Here, we study parallel divergence of wing colouration in the butterflies
Heliconius erato and H. melpomene, which are distantly related Müllerian
mimics that show parallel geographic variation in both discrete variation
in pigmentation, and quantitative variation in structural colour. Using
geographic cline analysis, we show that clines in these traits are
positioned in the roughly the same geographic region for both species,
which is consistent with direct selection for mimicry. However, the width
of the clines varies markedly between species. This difference is
explained in part by variation in the strength of selection acting on
colour traits within each species, but may also be influenced by
differences in the dispersal rate and total strength of selection against
hybrids between the species. Genotyping-by-sequencing also revealed weaker
population structure in H. melpomene, suggesting the hybrid zones may have
evolved differently in each species; which may also contribute to the
patterns of phenotypic divergence in this system Overall, we conclude that
multiple factors are needed to explain patterns of clinal variation within
and between these species, although mimicry has probably played a central
role.