Australasian Science: Australia's authority on science since 1938

Blind Beetles Show Signs of Sight

A species of blind predatory water beetles that has been living in the aquifers beneath the Western Australian desert for millions of years still express opsin genes that are usually only found in species with eyes, according to research published in Royal Society Open Science.

“Opsin proteins form visual pigments which turn photons of light into a signal that is sent to the brain,” said Dr Simon Tierney of The University of Adelaide. “The presence of these gene products is unusual, not only because there is no light to activate the signalling pathways underground, but because these beetles are also eyeless.”

Tierney says that the genetic mechanisms that lead to the reduction of traits over time – or regressive evolution – has intrigued biologists because Darwinian views of evolution as an adaptive process may not necessarily apply. “These beetles have provided us with credible preliminary evidence for non-adaptive evolution,” he says. “Non-adaptive evolution or ‘neutral theory’ is when there is no selective pressure on a gene, resulting in an accumulation of random mutations in the gene sequence over time,” he says.

Tierney’s team compared three subterranean beetle species with two closely related surface-dwelling species. Opsin gene products were found in all surface species and in one of the three subterranean beetle species studied.

“Our results broadly conform to non-adaptive evolutionary theory, and the discovery of a functional opsin in one underground species may indicate either a secondary role for opsin, known as pleiotropy, or the amount of time spent underground,” Tierney says.