Fish evolution has scientists seeing blue

12 Jan 2015

Research into the genetics of fish vision has discovered evidence of a little-known alternative form of evolution.

QBI scientists at The University of Queensland (UQ) worked with the University of Basel to discover that a family of genes responsible for blue vision in percomorph fishes – including species such as tuna and anglerfish – has undergone concerted evolution, where related genes stay closely aligned.

The study’s co-lead author, Dr Fabio Cortesi a visiting scholar to QBI, said the evolutionary path taken by these genes led to them having very similar attributes instead of diverging.

“We found that evolution doesn’t always go as assumed, and a different type of evolution occurred for these genes in these fishes,” Dr Cortesi said.

“Instead of genetic changes slowly accumulating over time, concerted evolution actually kept different genes within the family very similar,” he said.

“If one of the genes started to diverge from the other genes within the family, concerted evolution occurred and it got pulled back in again to where it started, keeping the genes functioning within a limited range.

“The concept had so far been more disproven than proven, but this is one of the first studies to comprehensively show it in a gene family across a lot of species.”

Dr Cortesi said the discovery was made amidst another finding of a new gene for blue colour vision in fishes.

“We originally found an extra gene for blue colour vision in one fish species, and then we looked at the genomes of nearly 100 other fishes to see if this particular gene had been overlooked previously,” Dr Cortesi said.

“Not only did this new gene for blue colour vision exist in some of the other fishes we checked, but when comparing the evolutionary history of blue genes between species we discovered attributes that point towards concerted evolution.

“It’s possible this is happening in a lot of other gene families as well, but scientists just haven’t been looking at a broad enough scale.”

QBI’s Professor Justin Marshall said that studying the visual systems of fish provides an insight into human biology as well as aquatic animals.

“Visual systems in land animals are much simpler because our visual environment is quite constant, whereas aquatic animals have to deal with differences in depth and particles in the water, such as sand or algae, creating different levels of light,” Professor Marshall said.

“Vision in humans has evolved to see in three colour channels – red, blue and green.

“In our case, the red and green colour receptors arose through a genetic duplication, similar to the new blue gene we found in fishes, however, before these genes split our ancestors were functionally dichromatic, comparable to some colour blind humans nowadays.”

The study was led by researchers from the Zoological Institute of the University of Basel, and was conducted in collaboration with The University of Queensland, the University of Olso, The University of Western Australia, and the University of Maryland.

Findings of the research, “Ancestral duplications and highly dynamic opsin gene evolution in percomorph fishes”, are published in the Proceedings of the National Academy of Sciences.