The genetic architecture of adaptation: convergence and pleiotropy in Heliconius wing pattern evolution.

Unravelling the genetic basis of adaptive traits is a major challenge in evolutionary biology. Doing so informs our understanding of evolution towards an adaptive optimum, the distribution of locus effect sizes, and the influence of genetic architecture on the evolvability of a trait. In the Müllerian co-mimics Heliconius melpomene and Heliconius erato some Mendelian loci affecting mimicry shifts are well known. However, several phenotypes in H. melpomene remain to be mapped, and the quantitative genetics of colour pattern variation has rarely been analysed. Here we use quantitative trait loci (QTL) analyses of crosses between H. melpomene races from Peru and Suriname to map, for the first time, the control of the broken band phenotype to WntA and identify a ~100 kb region controlling this variation. Additionally, we map variation in basal forewing red-orange pigmentation to a locus centred around the gene ventral veins lacking (vvl). The locus also appears to affect medial band shape variation as it was previously known to do in H. erato. This adds to the list of homologous regions controlling convergent phenotypes between these two species. Finally we show that Heliconius wing-patterning genes are strikingly pleiotropic among wing pattern traits. Our results demonstrate how genetic architecture can shape, aid and constrain adaptive evolution.