Sexual selection saves, says study

By Lindsey Woods

By Brandon Smith, Contributing Writer

Imagine there are 10 ladies in a room with 40 prospective fellows. The girls know exactly which type of guy they would like to be seen with in public, and the guys aren’t that picky. But there is a catch—the girls each have to pick their one guy in the dark.

In some respects, that is what some species are being forced to deal with. Entire genetic lines of fish are at risk because toxic waste has literally “muddied up the waters” and reduced visibility at mating time. But a new study conducted by the University of British Columbia and the International Institute for Applied Systems Analysis holds out hope for preserving these and other species.

Choosing the right sexual partner may be a defining factor for maintaining species variation within a relatively narrow niche, according to the study. This idea threatens the widespread view that similar species sharing the same habitat and resources cannot coexist over a long period of time.

Sexual selection is the term used to describe a female’s highly selective nature. Females will often only mate with the strongest, healthiest and most attractive male of their species to better ensure their offspring will carry on those positive traits.

The team, led by Dr. Leithen M’Gonigle from the Department of Environmental Science, Policy, and Management at The University of California at Berkeley, published its findings April 1 on the website of the scientific journal Nature.

The findings, based on computer modelling, challenge the body of evidence that natural selection is the driving force behind a species’ survival.

“I think most evolutionary biologists today are of the opinion that sexual selection is not really an important process maintaining biodiversity,” M’Gonigle said. “Hopefully our paper can help change that opinion.”

There may be conservation implications in proving findings like this as well, he said. One example used in the study focused on Lake Victoria in eastern Africa.

The lake is the second largest body of fresh water by area in the world and home to a diverse population of fish commonly called cichlids. According to the authors, human activity in the lake has led to the extinction of many varieties of these colorful fish.

“There has been an extensive loss of biodiversity in cichlid fish within Lake Victoria due to eutrophication (a takeover by algae) of the lake,” said Dr. Sarah Otto, a co-author of the study. “It is much cloudier, making it difficult for the fish to see and distinguish their mates.”

A body of water may become eutrophic after being exposed to large amounts of chemicals like nitrogen and phosphorous found in fertilizers and detergents. The process increases the mineral richness of the lake, dramatically decreasing visibility and depleting oxygen fish need to survive.

The situation in Lake Victoria is a visible instance of the importance of sexual selection. According to the study, there are hundreds of cichlid species in the lake competing for the same resources.

“As human activities are elevating turbidity levels in Lake Victoria, the female cichlids are becoming less able to discern between males of different species and consequently are often mating with the wrong types,” M’Gonigle said. “I would hope that our results have some implications for conservation.”

Michelle Rafacz, assistant professor in biology in Columbia’s Science and Mathematics Department and an adjunct scientist in the Lincoln Park Zoo’s Conservation and Science Department, said she strongly believes in the value of conservation efforts.

“I do believe this study might have implications for future generations of endangered or threatened species, especially with regard to effects of habitat loss and climate change,” Rafacz said.

If a species is in so endangered that it cannot recover without intervention, conservation efforts would be the next step in preserving a species, according to her.

“It all depends on population size of endangered species,” Rafacz said. “Without enough females with preferences for particular males, the mechanism simply won’t work and natural selection will be the driving force in adaptations.”