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Sex: It's Costly But Worth It. Just Ask A Microbe

February 8, 2006
McMaster University
Microbes were assumed to be asexual organisms, but a study shows that they also produce offspring when they mate with other microbes. When mating with other microbes, however, a fair bit of flirting and fluffing goes on in their mating ritual, which draws on the microbe's energy reserves, and ultimately affects the quality of their offspring.

The next time you mutter about the high cost of relationship maintenance, take comfort in knowing that microbes share your pain. In the first study to examine the cost of sexuality in microbes, Jianping Xu, associate professor of biology at McMaster University, found that sex exacts physical, morphological and behavioural stress on microbes. His findings are published in the recent edition of Genetics, published by the Genetics Society of America.

"There was always an assumption that microbes reproduce asexually, but they are actually asexual and sexual," says Xu. Using a fungus that has two sexes, A and Alpha, he established three populations: A microbes (females), Alpha microbes (males), and a combination of the two. When left to re-produce on their own, the first two groups of microbes performed efficiently and prolifically. The microbe couples, however, were slower to reproduce. But Xu also found that a fair bit of fluffing and flirting goes on when mixed pairs slide into a petri dish, and the results can be detrimental to their fitness.

"We noticed that mating stunted their asexual reproduction because each partner spent more time attracting the other than nourishing its own growth," explains Xu. "Transmitting mating signals costs both partners: one partner uses up materials and energy to produce and transmit the signal, and the other partner gets distracted by the mating signal and loses interest in reproducing on its own."

The irony is that despite the high cost of sex there are benefits.

"In many microbes, mating and sexual reproduction produce genetically diverse and hardy progeny better able to withstand environmental changes, inhospitable conditions, lack of water, extreme temperatures and fewer nutrients," says Xu.

There may be other benefits, too. "Every time DNA replicates and the microbes reproduce, mutations are introduced. While some mutations may be beneficial, most have no effect or are deleterious," says Xu. "Through mating and sexual reproduction, mutations accumulated in different strains are brought together so that deleterious ones are purged more efficiently, and the beneficial ones are brought together to produce fitter offspring."

As Xu found out, some of those mutations reduced the cost of interacting with sexual partners. The downside is that the same mutations can also reduce their mating ability. "There is some kind of balance out there between the cost and benefit of sex," says Xu. "And we are looking into that right now".


Funding for this study was provided in part by the Natural Science and Engineering Research Council of Canada.

McMaster University, a world-renowned, research-intensive university, fosters a culture of innovation, and a commitment to discovery and learning in teaching, research and scholarship. Based in Hamilton, the University, one of only four Canadian universities to be listed on the Top 100 universities in the world, has a student population of more than 23,000, and an alumni population of more than 115,000 in 128 countries.

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McMaster University. "Sex: It's Costly But Worth It. Just Ask A Microbe." ScienceDaily. ScienceDaily, 8 February 2006. <>.
McMaster University. (2006, February 8). Sex: It's Costly But Worth It. Just Ask A Microbe. ScienceDaily. Retrieved May 23, 2017 from
McMaster University. "Sex: It's Costly But Worth It. Just Ask A Microbe." ScienceDaily. (accessed May 23, 2017).