Reproductive isolation caused by colour pattern mimicry

Abstract

Speciation is facilitated if ecological adaptation directly causes assortative mating, but few natural examples are known. Here we show that a shift in colour pattern mimicry was crucial in the origin of two butterfly species. The sister species Heliconius melpomene and Heliconius cydno recently diverged to mimic different model taxa, and our experiments show that their mimetic coloration is also important in choosing mates. Assortative mating between the sister species means that hybridization is rare in nature, and the few hybrids that are produced are non-mimetic, poorly adapted intermediates. Thus, the mimetic shift has caused both pre-mating and post-mating isolation. In addition, individuals from a population of H. melpomene allopatric to H. cydno court and mate with H. cydno more readily than those from a sympatric population. This suggests that assortative mating has been enhanced in sympatry.

No evidence for maintenance of a sympatricHeliconiusspecies barrier by chromosomal inversions

“…2012), and prezygotic isolation in the form of mate preference is almost complete (Jiggins et al. 2001). Therefore, inversions may not be necessary for divergent loci to accumulate between the species.…”

Host plants and immatures as mate-searching cues in Heliconius butterflies

“…Such colorations probably function to advertise larval toxicity to predators, and, although few cases of mimetic convergence have been proposed, they could also provide species-specific information to searching males (Brown & Benson 1977). Signals that have evolved in a defence context are often also used in intraspecihc signalling (Summers et al 1999;Weller et al 1999;Jiggins et al 2001). For example, females of the pipevine swallowtail butterfly, cued by conspecific larval warning colorations, avoid oviposition on occupied plants, which probably reduces competition for their offspring (Papaj & Newsom 2005).…”

Beauty in the eye of the beholder: the two blue opsins of lycaenid butterflies and the opsin gene-driven evolution of sexually dimorphic eyes

“…We hypothesize that the blue opsin gene duplication and the associated evolution of the 500·nm visual pigment may be causally linked to the radiation of this family that is famous for blue butterflies, including Nabokov's Blues (Tribe Polyommatini) (Nabokov, 1945). While cues from UV, LW and polarized light (Silberglied, 1984;Jiggins et al, 2001;Fordyce et al, 2002;Sweeney et al, 2003) have been recognized as important social signals in butterfly communication, our data suggest that blue cues in blue butterflies may provide an equally important signal for visual communication.…”