THE GENETIC-BASIS OF AN ADAPTIVE RADIATION - WARNING COLOR IN 2 HELICONIUS SPECIES

Mimetic colour pattern races of Heliconius butterflies provide a strik ing example of adaptive radiation and numerous crossing experiments ha ve investigated the genetics of these racial differences. However, col our pattern differentiation between closely related Heliconius species has not been previously studied. Here we present data from crosses be tween H. erato cyrbia and its sister species, H. himera. The genetic a rchitecture underlying colour pattern divergence between these species is identical to that observed between races of H. erato. As in inter- racial crosses, colour pattern differences resulted from segregation a t a few major loci. Evidence from 1321 offspring in 4 F-1; 17 backcros s, 7 F-2 and 21 further crosses showed that two major loci controlled most of the colour pattern differences between H. erato and H. himera. There were strong interactions between these loci in their patterns o f expression and evidence for other loci with relatively minor phenoty pic effects. More importantly, based on patterns of expression within broods and linkage with Aconitase, we conclude that these major loci w ere homologous with those known to be responsible for colour pattern d ifferences within H. erato. Our crosses also permit a re-evaluation of the relationships between colour pattern races of H. erato. This sugg ests that H. e. hydara, which occurs across a major mtDNA break, is th e ancestral phenotype from which other races have evolved. Based on th is assumption, we find no evidence to support the recent suggestion th at apparently homologous colour pattern alleles have arisen multiple t imes.