Asexual Ants Give up on Males
April 15, 2009 -- "Men, who needs them?" is a question sometimes uttered by frustrated women, but a widespread species of tropical ant has taken that position to the extreme by becoming asexual and only producing females, according to a new study.
The insect, Mycocepurus smithii, represents the first documented male-less species of ant, the scientists believe. What's more, all of its female ant colonies are thriving on clonal fungi, and appear to have stopped producing males a long time ago, puzzling experts who believe asexuality is evolutionarily disadvantageous.
Lead author Anna Himler explained that a life without sex might not be so bad after all.
"Sexual reproduction is costly in several ways and asexual reproduction -- the lack of sex -- can be advantageous," she said, offering four reasons.
First, "asexuality avoids the energetic cost of producing males, and thus doubles the number of reproductive females produced each generation from 50 percent to 100 percent of offspring," said Himler, a researcher at the University of Arizona's Center for Insect Science.
She added there is no need to expend energy trying to find a partner, genes are not broken up, and "the risk of contracting sexually transmitted diseases or parasites" goes out the window.
The two main advantages for sexual reproduction, she said, are more effective elimination of deleterious gene mutations and "faster evolution via mixing genes with those of a mate."
For the study, published in the latest Proceedings of the Royal Society B, Himler and her colleagues conducted field surveys at hundreds of nests for the ant in Panama, Guyana, Ecuador, Peru, Argentina and Brazil. The scientists failed to find any males.
They then collected colonies from five Panama populations of the ant and put them through a barrage of tests. DNA extracted from offspring showed that they were all clones of their mothers. Dissections of colony queens revealed they not only hadn't mated, but their mating apparatus had degenerated, indicating the species has probably been reproducing asexually for a long time.
Since certain bacteria can curb sexual activity in insects, the scientists tested for the presence of those, and even administered antibiotics to see if they could "cure" the ants of their no-sex state. Nothing happened.
Finally, they conducted "a fungal-switch experiment," whereby the ant's normal fungus garden -- which also happens to be asexual -- was replaced with a different fungus. The queen ants produced workers first but, again, all females.
Aside from having a sexless existence, the lack of males doesn't appear to change the ants' lives much since, as Himler explained, "in most ant species, males have little to no role in the daily activities of the ant colony...[so] the absence of males does not generate extra work for the female worker ants."
Jacobus Boomsma, director of the Center for Social Evolution and a professor in the Department of Biology at the University of Copenhagen, told Discovery News, "Time will tell whether this ant is an ancient 'asexual scandal' that flies in the face of commonly accepted theory or whether there is a good explanation, albeit perhaps an unusual one."
His "hunch is that the answer lies in this ant being extremely Catholic in its association with a wide array of fungal partners."
Humans are, of course, a sexual species, but "in theory, genetic engineering could in the distant future enable male-less reproduction," Himler said. "A female could then reproduce without any male mate, whereas a male would still need a female mate to reproduce because males don't have the reproductive machinery to make babies."
She added, "How such theoretical societies would look is difficult to predict."