Males need not apply: research on grasshopper species unravels the benefits of giving up sex

Face of Warramaba flavolineata, one of the two sexual species that crossed to form the parthenogen Warramaba virgo
Face of Warramaba flavolineata, one of the two sexual species that crossed to form the parthenogen Warramaba virgo. Image: Professor Michael Kearney

A unique all-female species of grasshopper that can reproduce without sex provides fascinating insights into evolution, new research led by the University of Melbourne has found.

Published today in Science, the research shows the Australian grasshopper Warramaba virgo (W. virgo) – a parthenogenetic species, meaning it can reproduce asexually by cloning itself – was just as ecologically successful as its counterparts that breed by sex.

Lead author Professor Michael Kearney said the findings were significant because they challenged current evolutionary theory about the advantages of sexual reproduction.

“Most species on earth have two sexes, male and female, that mix their genes when they reproduce. This method of reproduction is thought to increase genetic diversity and ecological success of a species,” Professor Kearney said.

“Parthenogenetic species in theory should be suffering from parasites and a high load of bad mutations. Our study finds no disadvantage to W. virgo compared to other species of grasshoppers that sexually reproduce. In fact, W. virgo has even managed to successfully spread from the west to the east of Australia, unlike its sexual relatives.”

Co-author Professor Ary Hoffmann said sexual reproduction could be costly.

“Finding a mate takes time and energy and comes with an increased risk of predation. 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?” Professor Hoffmann said.

The study looked at more than 1500 genetic markers to assess the genetic diversity in the W. virgo and found almost no variation, in striking contrast to related species of grasshoppers that sexually reproduce.

“The species appears to have developed from only a single highly successful clone,” Professor Hoffmann said.

While parthenogenetic species are extremely rare, some do occur in Australia. The W. virgo is estimated to have evolved from a hybrid mating between two other grasshopper species (W. whitei and W. flavolineata) more than 250 thousand years ago.

“With so many benefits of giving up sex, it’s surprising that parthenogenetic species are not more common. Our research proposes this rarity is most likely due to constraints on origin rather than rapid extinction,” Professor Kearney said.