Scientists measure genetic variation among animals transitioning from one species to two

New research highlights the “gray zone” of speciation, the intermediary or transitionary zone in which one species become two.

The study, published this week in the journal PLOS Biology, features a new method for measuring genetic divergence. The authors, a team of French biologists, modeled the varying — and sometimes contradictory — effects of natural selection, drift and migration rates on animal genomes.

These factors affect different parts of the genome in unique ways. Teasing apart these effects allowed researchers to see new patterns of variance and identify those corresponding to species divergence.

The analysis revealed a genomic gray zone featuring molecular divergence measuring between 0.5 and 2 percent difference. It is in this gray zone that two not-yet diverged species or populations can continue to interbreed and exchange genes.

In this gray zone, some genes continue to be freely exchanged between populations while others remain isolated — encouraging both speciation and genetic diversity.

Analysis of 61 population pairs, including mussels, gorillas, trumpet worms, earthworms, butterflies and mosquitoes, proved speciation among all species is limited by the confines of the same genomic gray zone. In other words, the pattern of speciation and genomic divergence holds true across a variety of animal types.

“Our report of a strong and general relationship between molecular divergence and genetic isolation across a wide diversity of animals suggests that, at the genome level, speciation operates in a more or less similar fashion in distinct taxa, irrespective of biological and ecological particularities,” researchers concluded.