How New Species Emerge: Genetic Reproductive Barriers May Not be Key

Evolution helps drive the emergence of new species. Yet exactly how new animals and plants arise has baffled scientists for years. Now, researchers have taken a closer look at how new species emerge, revealing that it may not be reproductive barriers that are the driving force behind speciation.

Speciation is the formation of barriers to reproduction between populations. These barriers can be either geographic or genetic. Geographic barriers can include mountains, rivers or glaciers that physically separate populations to the point where the groups begin to evolve into different species. Genetic differences, in contrast, prevent individuals from producing fertile offspring.

Yet these reproductive barriers may not actually be driving speciation. In order to learn exactly what might be driving it, the researchers compared speciation rates to genetic indicators of reproduction isolation in birds and fruit flies. They used evolutionary tree-based estimates of speciation rates for nine major fruit fly groups and two-thirds of known bird species.

"Most research on the formation of species has assumed that these types of reproductive barriers are a major cause of speciation," said Daniel Rabosky, one of the researchers, in a news release. "But our results provide no support for this, and our study is actually the first direct test of how these barriers affect the rate at which species form."

In the end, the researchers found that while reproductive barriers are still important on some level, the rate at which genetic reproductive barriers arose did not predict the rate at which new species form in nature. This, in turn, seems to imply that some other mechanism is helping drive speciation and that the current understanding of how species form is extremely incomplete.

"The whole enterprise of finding 'speciation genes' is potentially irrelevant to understanding the origin of species," said Rabosky in a news release. "But our study is certainly not going to be the final word on this. If anything, our results indicate that a lot more data will be needed before we can conclusively link the mechanisms we usually study in the lab to the patterns of species formation we see in the natural world."

So what is driving speciation? What's missing from the current picture is extinction. It's possible that speciation might be limited primarily by factors associated with the persistence of new species. While it may be relatively easy for a species to split into two new species, the vast majority of new species do not persist for long periods.

The findings are published in the journal Proceedings for the National Academy of Sciences.