These grasshoppers haven't had sex in 250,000 years, and they're thriving
Warramaba virgo are exclusively females, and they have an ability to create perfect clones of themselves
An all-female species of grasshopper in Australia that ditched reproductive sex in favour of self-cloning is doing just fine, thank you very much.
Scientists at the University of Melbourne did a deep dive on the overall well-being of the Warramaba virgo, a type of grasshopper that's been reproducing asexually for 250,000 years, in a phenomenon known as parthenogenesis.
The findings, they say, challenge our ideas about the advantages of sexual reproduction, which is widely viewed as a way of diversifying the gene pool and safeguarding against parasites, mutations and bad genes.
"So we were thinking, well, you know, would these parthenogens be loaded with parasites and sick with mutations?" biosciences professor Michael Kearney told As It Happens guest host Tom Harrington. "So we went to look at how well they're doing, basically. And we found they're doing really well. No problems."
The study by Kearney and his colleagues was published in the journal Science.
Parthenogenesis is a form of asexual reproduction in which an embryo develops without fertilization from sperm. It is extremely rare in the animal kingdom, though not unheard of. Kearney estimates it occurs in about one in 1,000 species.
Most species that do it are bugs or reptiles, though it has also been observed in some fish and amphibians. Mammals can't do it at all. On rare occasions, birds can adopt this technique when the females don't have access to males, though it tends to result in short-lived and unhealthy offspring.
But W. virgo has got it down to a science.
"It's evolved a way of getting rid of the males. It's actually tweaked its meiosis, which is the way the sex cells are produced, so that it it actually doubles the chromosomes," Kearney said. "It basically means perfect cloning. So they are able to just produce eggs that are all female, that are identical to themselves, with no males necessary."
And they really are identical, he said. A genetic examination of the population suggests they've all evolved from a single female, about quarter of a million years ago.
That female, Kearney said, was the product of hybridization, or cross-mating, between two similar grasshopper species. "It's like a horse and a donkey crossing to make a mule," he said.
But while a mule has advantages in strength and endurance over its predecessors, Kearney says these female grasshoppers don't seem to be any better or worse off than the species they came from.
The researchers examined 14 traits to measure their physical fitness, including how many eggs they lay, how long they take to mature, their heat tolerance and their resistance to water loss. Overall, the all-female grasshoppers squared up evenly against the other two species.
"There was no super power, but neither was there any evidence of a loss of fitness because of mutations or disease. So they were just somewhere in the middle, nothing particularly special," he said.
Insects are very old — and very diverse
Dan Johnson, an environmental scientist at the University of Lethbridge and president of the Entomological Society of Alberta, says the study's findings are interesting, but not surprising.
"There are many species of insects that have gone for a long, long time [without sexual reproduction] and they're perfectly healthy," he said.
After all, he says, insects have been around for millions of years, predating even dinosaurs. As a result, they display an incredible diversity when it comes to their mating habits.
There are mites, for example, that can lay unfertilized eggs, which then become male offspring that can then mate with their mother. There are also grasshoppers in the Canadian Prairies that engage in group sex, with one female and up to seven males.
There may even be grasshoppers in Alberta that are parthenogenetic, just like W. virgo. Johnson says he and his colleagues have never seen a male three-lined shieldback in the province.
"But the weird thing is in B.C., males and females are all over the place. If you went out and collected 500, you probably have half and half male and female. But here in Alberta, only females," he said. "So we're wondering what's going on. At least I am."
Advantages of sex-free reproduction
So why do the Australian grasshoppers do it this way? Scientists don't know for sure. But there are some pretty big advantages to asexual reproduction.
"Imagine you've got a species that has half males, half females, and it switches over to having all females. That means that the reproductive rate doubles because there are twice as many individuals having babies," Kearney said. "So it is a massive advantage, in fact, to parthenogenesis, at least in the short term."
What's more, sexual reproduction has its disadvantages.
"Finding a mate takes time and energy and comes with an increased risk of predation," Ary Hoffman, a co-author of the study, said in a press release. "If we can do away with males and still have viable offspring and the species thrives, then why do we bother with sex at all?"
Written by Sheena Goodyear. Interview with Michael Kearney produced by Aloysius Wong.