MALE BUTTERFLIES HAVE genes which give them a sexual reference for a partner that looks like them, according to new research.

In a study published in the open-access journal PLOS Biology, a team of academics from the University of Cambridge, in collaboration with the Smithsonian Tropical Research Institute in Panama, observed the courtship rituals and sequenced the DNA from nearly 300 butterflies to find out how much of the genome was responsible for their mating behavior.

This is one of the first ever genome studies to look at butterfly behavior and researchers said it unlocks the secrets of evolution to help explain how new species are formed.

The scientists sequenced the DNA from two different species of Heliconius butterflies which live either side of the Andes mountains in Colombia. Heliconians have evolved to produce their own cyanide which makes them highly poisonous and they have distinct and brightly colored wings which act as a warning to would-be predators.

Professor Chris Jiggins of the University of Cambridge, one of the lead authors on the paper, said: “There has previously been lots of research done on finding genes for things like color patterns on the butterfly wing, but it’s been more difficult to locate the genes that underlie changes in behaviour.

What we found was surprisingly simple – three regions of the genome explain a lot of their behaviours. There’s a small region of the genome that has some very big effects.

The male butterflies were introduced to female butterflies of two species and were scored for their levels of sexual interest directed towards each. The scientists rated each session based on the number of minutes of courtship by the male – shown by sustained hovering near or actively chasing the females.

Unlike many butterflies which use scented chemical signals to identify a mate, Heliconians use their long-range vision to locate the females, which is why it’s important each species has distinct wing markings.

When a hybrid between the two species was introduced, the male would most commonly show a preference for a mate with similar markings to itself. The research showed the same area of the genome that controlled the coloration of the wings was responsible for defining a sexual preference for those same wing patterns.

Dr Richard Merrill, one of the authors of the paper, based at Ludwig-Maximilians-Universität, Munich, said: “It explains why hybrid butterflies are so rare – there is a strong genetic preference for similar partners which mostly stops inter-species breeding. This genetic structure promotes long-term evolution of new species by reducing intermixing with others.”