Fish are Having Gentler Sex Because of Human Influence?

Experts have long known that human activity can influence how local animals live, including their habitats, food sources, and even behavior. However, a new study has found that we can even impact how an animal procreates, changing the size and structure of specific fish species' genitalia in only a few decades.

The study, recently published in the journal Evolutionary Applications, details how the male genitalia of three different species of Bahamian mosquitofish (Gambusia) living in water heavily influenced by human activity have undergone a rapid and surprising change.

Stunningly, the highlighted changes are not mere mutations risen from chemical dumping or other taboo industrial activities. Instead, these appear to be natural changes, and the waters in question were simply split from larger habitats with the building of roads in a process called "fragmentation."

Fragmentation is not a new concept for researchers. Nature World News has previously reported on how fragmentation is leading to massive declines in New England cottontail populations. Similarly, the once proud mountain lions of the Santa Monica Mountains have degraded to inbreeding and patricide to survive, cut off from the rest of the world by the Southland freeways.

However, according to researchers from North Carolina State University, this latest fish study provides the first example of rapid physiological accompanying fragmentation.

"This study shows that human-induced habitat alteration results in changes in fish genitalia in just 35 to 50 years - the time elapsed since the fragment-causing roads were built," researcher Justa Heinen-Kay said in a release.

So what kind of changes are occurring? Based on observations from earlier work, the researchers theorized that mosquitofish traditionally boast long and bony gonopodium tips - the organ that transfers sperm into a female for live-bearing birth.

"When predators are around, G. hubbsi males spend a lot of time attempting to mate with females because of the high mortality rate," Heinen-Kay explained. "These bonier and more elongated gonopodium tips [are] a way to copulate even when females don't cooperate."

However, a smaller habitat leads to fewer predators and less pressure to mate. The researchers observed that fragmented male mosquitofish were boasting gentler gentiles for less frantic copulation, compared to their unfragmented cousins' blunt instruments.

"Because genitalia have an obvious and direct influence on reproduction, these findings beg the question of whether human-induced environmental change might facilitate speciation," added study author Brian Langerhans. "How common this sort of rapid change in genital shape might be in other species, and its consequences for the formation of new species, are some of the questions we'll ask in future studies."