Studies say experiments in stickleback fish have shown for the first time that the evolution of new sex chromosomes is the driving force behind the formation of a new vertebrate species.
Up until now, most evidence has shown that new species arise because they have adapted to new environments.
But, according to a report in Nature News, scientists found that the emergence of new sex chromosomes caused a population of threespine stickleback fish in the Japan Sea, to diverge from its Pacific Ocean-dwelling ancestor (Gasterosteus aculeatus) - creating a new species.
Jun Kitano, an evolutionary biologist at Tohoku University in Japan, and his team discovered that the Japan Sea stickleback fish had different sex chromosomes compared to their ancestors.
The ancestral Y sex chromosome (which makes males) had fused with a non-sex chromosome to create a new sex chromosome in the Japan Sea stickleback fish.
The team also observed that the Japan Sea males exhibited more aggressive mating behaviors than their ancestral populations.
Females from the ancestral population avoid mating with the Japan Sea fish due to their more aggressive behaviour. And in lab tests, the male progeny of the two populations were sterile.
The study found that the gene responsible for the aggressive mating behavior of the Japan sea males was on the new Y chromosome.
The new mating behaviors linked to the new sex chromosome stop the two populations from mating, making the Japan Sea population a new species.
"There is a gene on the new sex chromosome that causes differences in mating behavior in the male stickleback. This behavior leads to evolution of a new species of stickleback," said Catherine Peichel, a molecular biologist at the Fred Hutchinson Cancer Research Center in Seattle, Washington, and a member of the research team.
According to Ole Seehausen, a fish ecologist and evolutionist at the Swiss Federal Institute of Aquatic Science and Technology in Dubendorf, the study is "remarkable".
"This is the first study that has shown a direct link between the evolution of sex chromosomes in vertebrates and the evolution of a new species," he said.