Sexual competition makes animal populations more resilient

According to a new study from the University of East Anglia, animal populations have lower genetic quality and a higher risk of extinction without sexual competition and selection.

The experts found that forced monogamy leaves animal populations less resilient to environmental stressors like climate change.

The study was focused on flour beetles that had evolved under natural polyandrous mating patterns or monogamous mating patterns. The researchers investigated how the two groups responded to strenuous conditions.

 “Species around the world are undergoing mass extinction due to a range of factors such as climate change, habitat loss and genetic bottlenecks,” said study lead author Professor Matt Gage. “These different stresses can trap populations within a reinforcing feedback loop known as the extinction vortex. We used this extinction vortex scenario to experimentally measure the importance of sexual competition and choice for population resilience.”

The flour beetle populations examined for the study had been raised in a lab for 10 years. Some lines of beetles were forced to be monogamous with no sexual competition or choice, while others were allowed to engage in a polyandrous mating pattern where each female was given a choice of five males every generation.

After 95 generations of beetles were produced under the two conditions, the experts studied how the following 15 generations coped with different environmental and genetic stresses down a simulated extinction vortex.

“We mimicked ‘real life’ scenarios facing biodiversity today through repeated cycles of stress from food limitation, exposure to heatwaves, and being forced through a genetic bottleneck,” said Professor Gage.

“We found that beetles from the monogamous history of selection could not cope with environmental or genetic stress in the vortex. They were much more likely to decline, and all had become extinct by the end of the trial.”

“So the removal of competition and choice from reproduction had created populations that were weaker when facing environmental and genetic stress.”

“By contrast, beetles with a polyandrous background, where males had been forced to compete and females had been given the opportunity to choose their mates for reproduction, declined much more slowly with 60 percent of the population still alive at the end of the study.”

“It’s not clear whether the forces that operate in the struggle to reproduce are positive or negative for population resilience. Darwin famously felt sick when he looked at the tail of a peacock because he could not understand how such a flamboyant structure could evolve if it hampered survival, but our study clearly shows how important this sexual selection is for maintaining wider population health.”

“Our long-term experiment suggests that sexual selection is a positive force for population resilience by purging out bad genes and fixing in good genes, improving a population’s overall genetic quality and therefore resilience for facing harsh environments or genetic stress.”

According to the researchers, the findings should apply to any species that reproduces sexually, experiences some degree of sexual selection, and faces environmental stress. The research may ultimately help with conservation management and captive breeding practices. 

“We propose that, if an endangered species has an evolved mating pattern where competition and choice is evident, then that opportunity should wherever possible be given to maintain genetic health,” said Professor Gage. 

The study is published in the journal Global Change Biology.

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By Chrissy Sexton, Earth.com Staff Writer