Data from: Ecological and genetic factors influencing the transition between host-use strategies in sympatric Heliconius butterflies

Shifts in host-plant use by phytophagous insects have played a central
role in their diversification. Evolving host-use strategies will reflect a
trade-off between selection pressures. The ecological niche of herbivorous
insects is partitioned along several dimensions, and if populations remain
in contact, recombination will break down associations between relevant
loci. As such, genetic architecture can profoundly affect the coordinated
divergence of traits and subsequently the ability to exploit novel
habitats. The closely related species Heliconius cydno and H. melpomene
differ in mimetic colour pattern, habitat and host-plant use. We
investigate the selection pressures and genetic basis underlying host-use
differences in these two species. Host-plant surveys reveal that H.
melpomene specializes on a single species of Passiflora. This is also true
for the majority of other Heliconius species in secondary growth forest at
our study site, as expected under a model of interspecific competition. In
contrast, H. cydno, which uses closed-forest habitats where both
Heliconius and Passiflora are less common, appears not to be restricted by
competition and uses a broad selection of the available Passiflora.
However, other selection pressures are likely involved, and field
experiments reveal that early larval survival of both butterfly species is
highest on Passiflora menispermifolia, but most markedly so for H.
melpomene, the specialist on that host. Finally, we demonstrate an
association between host-plant acceptance and colour pattern amongst
interspecific hybrids, suggesting that major loci underlying these
important ecological traits are physically linked in the genome. Together,
our results reveal ecological and genetic associations between shifts in
habitat, host use and mimetic colour pattern that have likely facilitated
both speciation and coexistence.