(040602 revised, 040317 created)
Evol Dev. 2003 May-Jun;5(3):269-80.
The Galton Laboratory, Department of Biology, University College London, London NW1 2HE, UK. russell.naisbit@unine.ch
Despite renewed interest in the role of natural selection as a catalyst for the origin of species, the developmental and genetic basis of speciation remains poorly understood. Here we describe the genetics of Mullerian mimicry in Heliconius cydno and H. melpomene (Lepidoptera: Nymphalidae), sister species that recently diverged to mimic other Heliconius. This mimetic shift was a key step in their speciation, leading to pre- and postmating isolation. We identify 10 autosomal loci, half of which have major effects. At least eight appear to be homologous with genes known to control pattern differences within each species. Dominance has evolved under the influence of identifiable "modifier" loci rather than being a fixed characteristic of each locus. Epistasis is found at many levels: phenotypic interaction between specific pairs of genes, developmental canalization due to polygenic modifiers so that patterns are less sharply defined in hybrids, and overall fitness through ecological selection against nonmimetic hybrid genotypes. Most of the loci are clustered into two genomic regions or "supergenes," suggesting color pattern evolution is constrained by preexisting linked elements that may have arisen via tandem duplication rather than having been assembled by natural selection. Linkage, modifiers, and epistasis affect the strength of mimicry as a barrier to gene flow between these naturally hybridizing species and may permit introgression in genomic regions unlinked to those under disruptive selection. Mullerian mimics in Heliconius use different genetic architectures to achieve the same mimetic patterns, implying few developmental constraints. Therefore, although developmental and genomic constraints undoubtedly influence the evolutionary process, their effects are probably not strong in comparison with natural selection.
Heliconius cydno: English name : the Cydno Longwing. A butterfly found in tropical rainforests of Central and South America. The host plant is passiflora (passion vine). Japanese name:シドノドクチョウ
H. melpomene: English name: the Cattle Heart. A "bowtie" butterfly
having beautiful jet black & bright red colors.. Japanese name: メルポメネドクチョウ
Epistasis: エピスタシス ((2つの遺伝子で，一方が他方の発現を抑えること))
canalization: can・al・ize
left: Heliconius melpomene, right : Heliconius cydno, center: their F1 hybrid.