Humans Inadvertently Changed This Fish's Genitals By Building Roads

Roads are made to lead from place to place, but a new study has found that they sometimes lead to evolutionary changes in animals, too.

Researchers at North Carolina State University say that road construction in the Bahamas has had a hand in altering the appearance and behavior of a small species of native fish, giving rise to what could be, potentially, a new species of mosquito fish.

Mosquito fish have always been abundant in the tidal creeks that extend inland on the Bahaman islands. Up until relatively recently, these fish pretty much looked and acted the same. But that's begun to change, thanks to human activity. In the middle part of last century, many of these narrow waterways were split by road crossings, and as a result, some populations of mosquito fish suddenly lost access to the ocean and continued to evolve in isolation.

Over the decades that followed in these mostly predator-free habitats, the mating behavior of mosquitofish began to change and, as researchers discovered, so did their genitalia. The rigid, elongated male sex organs typically found on mosquitofish had become ones that were apparently a bit more pleasing to their mates, the scientists said.

"Where there are lots of predators around, mating behaviors are very costly, so selection favors genitalia in males that increases speed and efficiency of fertilization, with or without the female's consent," lead researcher Brian Langerhans told The Dodo.

With fewer predators around, the fish are free to devote more energy on other activities - including mating.

"There is a lot more female preference in mating and more courtship behaviors," Langerhans said. "No longer is there this strong selection pressure to shape the genitalia in a manner that favors efficiency. We think that basically the females are asserting these preferences based on slight differences in male genitalia."

To the untrained eye, isolated fish's organs don't appear to be much different from each other. But the changes may be significant enough to consider it the formation of a new species - all because of the new roads.

"As populations become more and more different in their genital morphology, their ability to interbreed can decline, leading to speciation," he explained.

Human activity is, by and large, responsible for a huge loss of biodiversity across the globe. But Langerhans said the findings suggest that under certain cases it may produce more, and in ways science has yet to discover.

"In recent years, it's becoming increasingly clear that humans are driving rapid evolution in lots of organisms intentionally and unintentionally - usually unintentionally. But the extent to which these activities actually increase diversification is a question that we'll be asking a lot this century."