Sexually Selected Traits May Be Harmful When the Population Size Drops

A team of researchers recently used mathematical models to demonstrate the effects of sexual selection on animals’ abilities to adapt to environmental changes. Traits derived from sexual selection, such as oversized horns or the peacock’s beautiful tail, generally improve the species’ chance of success in a new environment. This benefit disappears in small populations, however, and the study has important implications for conservation biology. The details are in a paper that was just published in the Journal of Animal Ecology.

Sexual selection is a type of natural selection in which the traits that help an animal obtain a mate are passed down to offspring. Over time, this can lead to more complex, extravagant features and displays. Examples of traits that developed this way are the peacock’s colorful tail, the lion’s mane, and the oversized antlers of the male moose. These traits, often referred to as “ornaments” if the only purpose is to attract mates, can often put the male in danger. The male peacock’s feathers make them stick out to predators and the long tail can slow them down. If the benefits of being able to attract mates outweigh the costs of being vulnerable to predation, the trait persists and may become even more emphasized. Researchers have debated on whether or not these sexually selected traits will help or harm species that may decline due to climate change.

Researchers from Queen Mary University of London developed a computer model to predict how different species would cope with climate change. The team found that animals with sexually selected traits would be quicker to adapt to new environments. This only occurs in larger populations, however. In very small populations, extravagant features and displays could prove harmful. Species with these types of traits were at a higher risk of extinction in a changing environment once the population size dropped.

The team’s findings show that while sexually selected traits are usually beneficial, very small populations may be at risk. The same traits that may help an animal find a mate can also make them more vulnerable to predation and other dangers. In a small population, this can lead to the rapid decline of the species. The authors hope that their model and findings may help conservationists identify populations that are at the greatest risk of extinction.

REFERENCE

Carlos Martínez-Ruiz, Robert J. Knell. Sexual selection can both increase and decrease extinction probability: reconciling demographic and evolutionary factors. Journal of Animal Ecology (2016).

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