In the new study published in Nature Ecology and Evolution, a research team mapped the extensive and striking colour variation among the females of the bluetail damselfly (Ischnura elegans). In this damselfly species, there are three genetically determined colour forms in the females, one of which makes them look like males. These male-like females have an advantage because they avoid excessive mating harassment from the males. The study clarifies when, how and why this variation arose, and shows that this variation has been maintained over long evolutionary time periods through so-called balanced natural selection.

By sequencing the DNA of the three colour forms of the bluetail damselfly and comparing it to the two colour forms in its closely related tropical relative Ischnura senegalensis, the researchers were able to demonstrate that this genetic colour variation in females arose at least five million years ago; through several different mutations in a specific genetic region on the damselfly's thirteenth chromosome. Having located the gene behind the female colour variation, the researchers can now go further and identify different genotypes in the males, and in the aquatic larval stage of these insects.

The researches demonstrated that We now have a good knowledge base for investigating the colour variation over longer evolutionary time scales among other species of this damselfly genus, which occurs in Europe, Africa, Asia, Australia, North and South America. These new genetic results help us understand both the evolutionary processes that take place within a species, and what happens over longer evolutionary macroevolutionary time scales of tens of millions of years and across several different species.