Sex helps populations avoid extinction: Study

Competition among men for reproduction improves the genetic health of offspring, says a significant study, suggesting that "sexual selection" achieves this by acting as a filter to remove harmful genetic mutations.

It helps populations flourish and avoid extinction in the long-term, said the team from University of East Anglia (UEA). Sexual selection operates when males compete for reproduction and females choose, and the existence of two different sexes encourages these processes.

"It ultimately dictates who gets to reproduce their genes into the next generation -- so it is a widespread and very powerful evolutionary force," said lead researcher professor Matt Gage from UEA's school of biological sciences in a paper appeared in the journal Nature.

To uncover the role of sexual selection, the team evolved Tribolium flour beetles over 10 years under controlled conditions in the laboratory. The only difference between populations was the intensity of sexual selection during each adult reproductive stage. The strength of sexual selection ranged from intense competition and choice where 90 males competed for reproduction with only 10 females.

After seven years of reproduction under these conditions, representing about 50 generations, the study exposed the underlying genetic health of the resulting populations. They found that populations that had previously experienced strong sexual selection maintained higher fitness and were resilient to extinction in the face of inbreeding.

However populations that had experienced weak or non-existent sexual selection showed more rapid declines in health under inbreeding - and all went extinct by the 10th generation.

"The results show that sexual selection is important for population health and persistence, because it helps to purge negative and maintain positive genetic variation in a population," the authors wrote.

Biologists have long puzzled about how evolutionary selection, known for its ruthless requirement for efficiency, allows the existence of males -- when in so many species their only contribution to reproduction are spermatozoa.

The results help explain why sex persists as a dominant mechanism for reproducing offspring. In the absence of sex, populations accumulate deleterious mutations through a ratcheting effect where each new mutation takes a population closer to extinction.

"Sexual selection helps to remove those mutations, enabling populations to persist against the threat of extinction," the authors concluded.