Bahamas Mosquitofish Develop Longer Sex-Organ when Surrounded by Predators

Mosquitofish grows bonier, longer genitalia in the presence of predators, researchers find.

Previous research has shown that male Bahamas mosquitofish (Gambusia hubbsi) changes mating techniques- from elaborate sexual activities to forcing females into sex- when predators lurk around them.

But researchers at North Carolina State University found that these fish actually changed the shape of genitalia when they were surrounded by attackers. According to the study, fish living along predators have longer, bonier gonopodium tips.

The gonopodium is a one millimeter-long organ that transfers sperm. Previous research has shown that female mosquitofishes spend 80 percent more time with males that have bigger genitalia.

"When predators are around, G. hubbsi males spend a lot of time attempting to mate with females because of the high mortality rate," Justa Heinen-Kay, a PhD student at the university and one of the study authors, said. "We hypothesize that G. hubbsi have evolved these bonier and more elongated gonopodium tips as a way to copulate even when females don't cooperate."

"Essentially, males need to transfer as much sperm as possible as quickly as possible, and this shape difference could help facilitate that," Langerhans said.

For the study, researchers analyzed mating behavior of mosquitofish in the "blue holes" located in the Bahamas. These holes are caves that are filled with water and are unique because some of them have Gambusia predators while others don't, making them an ideal location to study fish behavior.

 "Comparing Gambusia across blue holes reveals that predation is associated with evolutionary changes in male genital shape," R. Brian Langerhans, assistant professor of biological sciences, and one of the study authors said in a news release. "It's a beautiful and elegant system to study the causes and predictability of evolutionary changes.

The study is published in the Journal of Evolutionary Biology.