An army of grasshoppers has taken over Australia. Marching across the continent from west to east, they’ve conquered new lands faster than rival species. The secret to their success? They’ve given up sex.
Warramaba virgo, the matchstick grasshopper, is an all-female species. There are no males in existence. Where most animals have two sexes that combine their genes when they reproduce, this species has evolved to cheat this fundamental process. Instead it reproduces solely by cloning (an egg can develop into an embryo without fertilisation).
She joins an exclusive female-only club that includes a bunch of other insects along with an assortment of vertebrates – fish, lizards and amphibians – and a host of spineless wonders only visible to microscope owners, but whose sex lives (or lack thereof) are exploding evolutionary paradigms.
Do all animals need to have sex to reproduce?
This entire self-replicating sisterhood of grasshoppers, which must number in the billions, originated from just one female – the hybrid daughter of two sexual Warramaba species that accidentally evolved the ability to clone herself around 250,000 years ago. Her subsequent reach and resilience as a species begs the question, why bother with sex at all?
This has been dubbed the ‘queen of questions’, perhaps the greatest riddle in evolutionary biology. Sex, you see, is expensive. As well as all the energetic inconvenience of finding and attracting a mate, sex cuts your reproductive potential in half, since only females can actually produce eggs.
All-female species can therefore proliferate at twice the rate of a sexual species. This makes them excellent colonisers of new territory, since they’re specialised for quick growth and fast dispersal, which is how this asexual grasshopper has outcompeted its sexual cousins. As Ary Hoffman, the lead scientist studying Warramaba virgo points out, with classic Aussie frankness, males in this scenario are reduced to ‘evolutionary wastage’.
What are the benefits of sexual reproduction?
Yet males, and indeed sex, prevails as nature’s reproductive norm. Scientific justification for the proliferation of such male profligacy has centred on two perceived evolutionary benefits of sex. Firstly, the combination of sperm and egg creates the genetic variation necessary for a species to adapt to new parasites, diseases and cope with environmental change. Secondly, it allows harmful mutations to get switched out of the gene pool.
Can all-female species ever thrive?
For this reason, all-female species have long been viewed as evolutionary dead ends with a limited shelf life of around 100,000 generations. Warramaba virgo, still going strong after 250,000 generations, makes males’ essential contribution to species longevity significantly less secure. Hoffman’s conclusion to his grasshopper study is that the rarity of all-female species is down to constraints on their origin and not, as previously assumed, their rapid extinction.
Main image: an illustration of Warramaba virgo. © Holly Exley