Having More Females Makes Maintaining Males ‘Cheaper’

Asexual animal populations sometimes struggle to support males, the non-reproductive gender—unless there is a higher proportion of females.

AsianScientist (Apr. 8, 2016) – For organisms with an option to procreate asexually—essentially, females breeding females without mating—supporting males, non-reproductive members of the population, becomes a matter of survival for the entire society. Now, a research team in Japan has shown that males can ‘cost’ less when there is a higher proportion of females.

The results of this study, published in Scientific Reports, may have broad implications for studies of the evolution and sustainability of sexual reproduction.

“It is typically known as the ‘twofold cost of sex,’” explained team leader and PhD student Kazuya Kobayashi from Kyoto University, referring to the fact that populations of sexual organisms grow at only half the rate of asexual ones.

“Purely in numerical terms, sexual reproduction presents a distinct disadvantage.”

But is the cost of supporting males really twofold?

“The dominance of sexual reproduction in the natural world is one of the great enigmas of evolutionary biology,” said Kobayashi.

“The fact that it persists in most organisms is an indication that its benefits outweigh the cost of supporting males. We wanted to quantify this difference.”

Kobayashi and a colleague studied a species of thunderbug, or onion thrips (Thrips tabaci), which has sexual and asexual strains that can be found residing on the same plant. They theorized that the sexual strain could increase its population, and thereby increase its competitiveness against the asexual strain, by lowering its ratio of males.

Using field studies as well as computer simulations, the team was able to demonstrate how lowering the cost of males boosted the sexual strain’s competitive advantage.

“When males cost less, the net-benefit of sexual reproduction increases,” said Kobayashi. He added that although many questions remain to be answered, “we anticipate that this finding will contribute to solving the puzzle of nature’s preference for sexual reproduction.”

The article can be found at: Kabayashi and Hasegawa (2016) A Female-biased Sex Ratio Reduces the Twofold Cost of Sex.


Source: Kyoto University.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

Asian Scientist Magazine is an award-winning science and technology magazine that highlights R&D news stories from Asia to a global audience. The magazine is published by Singapore-headquartered Wildtype Media Group.

Related Stories from Asian Scientist