盲水虱体内发现视力基因

University of Adelaide researchers have made a surprising discovery in the aquifers¹ beneath the Western Australian desert, which challenges the traditional Darwinian view of evolution. A team, lead by Dr Simon Tierney, discovered that a species of blind predatory water beetles³ -- living underground for millions of years -- express vision genes⁵ (opsin) which are usually only found in species with eyes. The research was published in the journal, Royal Society Open Science.

 

"Opsin proteins form visual pigments⁶ which turn photons of light into a signal that is sent to the brain. We expect to find opsin in beetles living above ground but to find them in those living in the dark is extraordinary," says Dr Tierney, a Postdoctoral Researcher from the University of Adelaide's School of Biological Science.

 

"The presence of these gene⁴ products is unusual, not only because there is no light to activate⁷ the signalling pathways (biochemical cascades) underground, but because these beetles are also eyeless," he says.

 

According to Dr Tierney, the genetic⁸ mechanisms⁹ that lead to the reduction of traits over time (regressive evolution) has intrigued¹⁰ biologists for hundreds of years because traditional Darwinian views of evolution as an adaptive process may not necessarily apply.

 

"Evolution is often perceived as a 'directional' or 'adaptive' process but this is not always the case. These beetles have provided us with credible¹¹ preliminary evidence for non-adaptive evolution," says Dr Tierney.

 

"Non-adaptive evolution or Neutral Theory is when there is no selective pressure on a gene, resulting in an accumulation of random¹² mutations in the gene sequence over time," he says.

 

Dr Tierney and his team used advanced molecular¹³ biology techniques (next-generation sequencing) to compare three subterranean¹⁴ beetle² species with two closely related surface dwelling¹⁵ 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 evolutionary¹⁶ theory and the discovery of a functional¹⁷ opsin in one underground species may indicate either a secondary role for opsin, known as pleiotropy, or the amount of time spent underground," says Dr Tierney.

 

To date, there are approximately 100 known subterranean beetle species living in isolated¹⁸ underground caves.

 

Dr Tierney believes these beetles will provide one of the most informative¹⁹ systems for biologists to explore the mechanisms responsible for regressive evolution because multiple comparisons can be made between species, which will produce a high sample size for statistical²⁰ assessment²¹.

 

"Our study has made a significant contribution in understanding how regressive evolution may operate under a non-adaptive evolutionary process," he says.

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