THE GENETIC ARCHITECTURE OF ADAPTATION: CONVERGENCE AND PLEIOTROPY IN HELICONIUS WING PATTERN EVOLUTION

Unravelling the genetic architecture of adaptive traits is a major challenge in evolutionary biology. Doing so informs our understanding of how traits evolve towards an adaptive optimum, the distribution of locus effect sizes, and how the genetic architecture of a trait affects its evolvability. The adaptive radiation of Heliconius butterflies is characterised by both intraspecific and interspecific wing pattern variation. While the genetic basis of some Mendelian variation is known in Heliconius melpomene and its mimic Heliconius erato, several wing pattern phenotypes in H. melpomene are yet to be mapped, and the genetics of quantitative phenotypic variation are poorly understood. We used QTL crosses between H. melpomene races from Peru and Suriname, to map for the first time, the control of the broken band phenotype to WntA. Additionally, we map a large effect locus Or that controls a large proportion of the quantitative variation in red-orange pigmentation, and which also modifies medial band shape variation in H. melpomene. We show that Or is homologous to the Ro locus in H. erato centred around the gene ventral vein lacking where it also affects medial band shape. This adds to the list of homologous regions controlling convergent phenotypes between these two species. Furthermore, we show Heliconius colour patterns appear to exhibit striking epistasis and pleiotropy across wing pattern traits and genes, which may enhance coadaptation across loci. Overall, our data further elucidates the genetic architecture of wing patterns in Heliconius, and how this architecture may be shaping, aiding and constraining adaptation across this radiation.