As they report in PLOS Biology, a University of Cambridge-led team examined patterns of assortative mating behavior among Heliconius melpomene and H. cydno, two butterfly species that live side by side, though rarely hybridize. The butterflies have differing wing color patterns, the researchers note, that are both warning signals to would-be predators and recognition signals for would-be mates.
The researchers conducted a genome-wide quantitative trait locus analysis of male preference behaviors among these butterflies — as determined by observing courtship rituals — to find three QTLs that explain 60 percent of mate choice behavior. One QTLs, the researchers note, is located close by to the optix gene, which is involved in giving the butterflies their patterns. This suggested to the researchers that this tight association might create a genetic barrier between the species.
"It explains why hybrid butterflies are so rare — there is a strong genetic preference for similar partners which mostly stops inter-species breeding," first author Richard Merrill from Ludwig-Maximilians-Universität, says in a statement. "This genetic structure promotes long-term evolution of new species by reducing intermixing with others."