Species: Paratrechina longicornis
Habitat: found throughout the tropics and subtropics, and many temperate zones it is one of the world's worst invasive species
Suppose you could have sex with your brother or sister, in the full and certain knowledge that any children would be safe from the harmful effects of inbreeding. Would you be more willing to commit incest?
The longhorn crazy ant certainly is. The queens regularly and willingly mate with their brothers, producing healthy offspring in the process. How do the parents manage this? Why, by cloning themselves of course.
Attack of the clones
Longhorn crazy ants get their "crazy" name from their rapid and erratic movements. They are ruthless opportunists, swarming on food sources in great numbers. They owe this ability to a sophisticated system of chemical communication, involving pheromones and other substances, which they use to coordinate their actions.
They have spread throughout the world, outcompeting other insect species and annoying humans in the process. The contained ecosystem of Biosphere 2, built in Arizona in the late 1980s, ended up overrun by longhorn crazy ants.
They are extremely effective invaders, readily setting themselves up in new areas. Yet such exploratory populations are typically small, and ought to quickly become inbred. This is bad news, because genetic defects have a chance to surface.
Not with your sister
Genes come in different forms called alleles, and most animals have two copies of each gene. In many cases, if an animal carries just one harmful allele no harm is done, because the other, "good" allele completely dominates it. Inbreeding removes this protection, as the offspring of closely related individuals are much more likely to end up with two copies of the harmful allele.
It may not be a hard-and-fast rule, but in general inbreeding is best avoided. Charles Darwin's children were blighted by early deaths and infertility, apparently because his family and his wife's were inbred. Human royalty from ancient Egypt to Victorian Europe have also practised inbreeding.
Longhorn crazy ants have got around these problems, and Morgan Pearcy, previously at the University of Lausanne in Switzerland and now at the Free University in Brussels, Belgium, has worked out how. With his colleagues he collected seven longhorn crazy ant nests from Bangkok, Thailand, in late 2008 and tracked them over several generations.
Chips off the old block
He found that when a queen ant makes a daughter queen she simply clones herself, laying an egg that is her genetic doppelganger. Things get more complicated when she makes a reproductive male, however. She mates with a male probably her brother if she doesn't look beyond her nest but their offspring contain none of her genetic material: they are simply clones of the father. As a result, the two siblings can breed while avoiding the problems associated with inbreeding: their offspring are genetically identical to their parents.
When it comes to making workers, the queens switch to normal sexual reproduction, mixing their own genes with those of the males often their brothers. As a result, the alleles get mixed together, but because these workers don't reproduce, there is again no danger that the problems associated with inbreeding will arise.
In the lab, queens readily mated with males from their own nest, even though those males were their brothers. Pearcy still has the nests in his lab, and despite several generations of ants mating with their siblings, there is no sign of harm. "They are doing fine," he says.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2010.2562
