New publication! Clines in iridescent structural colour

1 June 2020

We have a new paper out in Molecular Ecology where we investigate variation in iridescent structural colour in the mimetic butterflies Heliconius erato and Heliconius melpomene. Both of these species vary from having to blue iridescent colour in Colombia to being matt black in Panama.

In her PhD thesis work Emma Curran showed that the colour change is more gradual in H. melpomene than H. erato and this is most likely due to weaker selection acting on the colour in this species. She also investigated population genomic structure and fund that while H. erato clusters into two different groups in Panama and Colombia, H. melpomene doesn’t. While the colour change happens in a similar place in both species, strongly suggesting that mimicry between the species has been important in its evolution, the differences between species hint at different evolutionary histories.

This is the first time that variation in iridescent structural colour has been investigated in wild Heliconius populations. This trait is also different to the colour pattern traits that have most commonly been investigated in Heliconius because it is a quantitative trait, controlled by many loci, rather being controlled by a single genetic locus. Our results therefore also shed light on the major question of how differences in quantitative traits evolve.

Nicola and two other members of the Nadeau lab holding buttefly nets

We collected butterflies from along the Pacific coasts of Colombia and Panama to investigate how wing colour changed across this region.

Two butterflies mating

A hybrid zone in action: Heliconius melpomene individuals with different colours and patterns mate in the centre of the hybrid zone in southern Panama.

The populations not only differ in iridescent colour but also the presence of a yellow bar on the hind-wing. Hybridisation allows the exchange of genetic material between populations but the differences in colour remain. This suggests that natural selection is maintaining these differences and preventing complete homogenisation of the populations.