Mosquitofish genital shape linked to presence of predators

October 11, 2013
The male Gambusia hubbsi (a) and its sperm-transferring organ (b). The threat of predators is linked to differences in the organ tip’s shape (c).

(Phys.org) —When predators lurk nearby, male Bahamas mosquitofish (Gambusia hubbsi) change mating strategies, rejecting elaborate courting rituals for more frequent and sometimes forceful encounters with females.

But as a recent North Carolina State University study shows, mating strategies aren't the only things changing for G. hubbsi when predators abound. The shape and size of the 's genitalia are also linked to the presence or absence of predators.

NC State Ph.D. student Justa Heinen-Kay and assistant professor of biological sciences R. Brian Langerhans show, in a paper published in the Journal of Evolutionary Biology, that fish coexisting with predators have longer, bonier and more elongated gonopodium tips than fish living without threat of predation. The gonopodium is the sperm-transferring organ in these livebearing fish.

Longer, bonier and more elongated gonopodium tips are, of course, relative; in small fish, these organ tips are generally only 1 millimeter long. Yet the findings suggest that male fish under constant threat of serving as a predator's snack have evolved better ways to impregnate under these conditions.

"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 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.

The researchers conducted the study in so-called "blue holes" in the Bahamas. These "big test tubes" are caves that have filled with water in the past 17,000 years; Langerhans calls them aquatic islands in a sea of land. Some of these aquatic islands contain Gambusia , while others do not.

"Comparing Gambusia across blue holes reveals that predation is associated with evolutionary changes in male genital shape," Langerhans said. "It's a beautiful and elegant system to study the causes and predictability of ."

Explore further: New fish species offers literal take on 'hooking up'

More information: Heinen-Kay, J. and Langerhans, B. Predation-associated divergence of male genital morphology in a livebearing fish, Journal of Evolutionary Biology, October 2013. DOI: 10.5061/dryad.g9735

Related Stories

New fish species offers literal take on 'hooking up'

September 27, 2012

Fishing hooks aren't the only hooks found in east-central Mexican waters. A new species of freshwater fish described by a North Carolina State University researcher has several interesting – and perhaps cringe-inducing ...

Why guppies have genital claws

August 2, 2013

New research from evolutionary biologists at the University of Toronto shows that the male guppy grows claws on its genitals to make it more difficult for unreceptive females to get away during mating.

Male guppies ensure successful mating with genital claws

July 24, 2013

Some males will go to great lengths to pursue a female and take extreme measures to hold on once they find one that interests them, even if that affection is unrequited. New research from evolutionary biologists at the University ...

Guppies and sexual conflict? It's a genital arms race

June 3, 2013

(Phys.org) —It's not always easy to tell if a fish is male or female: they look more or less the same. But there are exceptions, such as guppies and, as with humans, guppy genitalia varies in size across the species.

Females choose sexier friends to avoid harassment

December 7, 2011

(PhysOrg.com) -- Scientists have observed a strategy for females to avoid unwanted male attention: choosing more attractive friends. Published today (7 December) in the journal Proceedings of the Royal Society B, the study ...

Recommended for you

Genome study offers clues about history of big cats

July 21, 2017

(Phys.org)—A large international team of researchers has conducted a genetic analysis and comparison of the world's biggest cats to learn more about their history. In their paper published on the open source site Science ...

Good fighters are bad runners

July 21, 2017

For mice and men, a strength in one area of Darwinian fitness may mean a deficiency in another. A look at Olympic athletes shows that a wrestler is built much differently than a marathoner. It's long been supposed that strength ...

Researchers discover mice speak similarly to humans

July 21, 2017

Grasshopper mice (genus Onychomys), rodents known for their remarkably loud call, produce audible vocalizations in the same way that humans speak and wolves howl, according to new research published in Proceedings of the ...

Researchers discover biological hydraulic system in tuna fins

July 20, 2017

Cutting through the ocean like a jet through the sky, giant bluefin tuna are built for performance, endurance and speed. Just as the fastest planes have carefully positioned wings and tail flaps to ensure precision maneuverability ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

tadchem
not rated yet Oct 11, 2013
The thesis here seems to be that rapid copulation with force is an adaptation of males faced with a threat they cannot overcome but must flee from?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.