NEW research shows the evolution of Australian rainbowfish was most probably caused by geological changes in the region, with the divergence into separate species probably occurring much earlier than previously thought.
A joint research initiative between the Western Australian Museum, Brigham Young University, and National Evolutionary Synthesis Center recently finished the most comprehensive phylogenetic analysis of rainbowfishes ever undertaken, which included virtually all rainbowfish species.
The research explored the biogeographic history of rainbowfishes in Australia and New Guinea, to determine how the various species are related to one another and how the geography of the region relates to their evolution.
Dr Peter Unmack says the study shows geography is a key indicator as to whether any two species of rainbowfish are closely related.
“We had collected samples extensively over the years and I began conducting DNA sequencing and gradually built a bigger and bigger data set,” he says.
“The major finding was the importance of geographic distribution, which confirms previous findings but this was a lot more thorough in that we had virtually all of the species included.”
The research also suggests rainbowfishes may be older than experts previously thought and provides a new framework for the timing of divergence within the family.
“The central Highlands of New Guinea have been going up very fast for the past five million years, and researchers previously thought that when the mountain range began to rise, the fish in the north were isolated from the fish in the south,” Dr Unmack says.
“We have shown that rainbow fish actually diverged much earlier than that, perhaps as much as 17-20 million years before the north-south separation. The geology suggests things should be young, but the genetics says things may be older than predicted.
“There was a lot of introgression among the groups.
“Essentially, some of the species within the group have mixed with other species at particular times in the past and then separated, and so have a lingering genetic history that includes the other species they’ve mixed with.
“Species breeding with other species creates gene flow between species, and yet rainbowfishes still maintain themselves as separate entities.”
Researchers also documented 15-20 undescribed species of rainbowfish, with as many as 10 of these occurring in Australia.
“Rainbowfishes are a very important Australian group, one that we consider well studied, and that has been very actively worked on for 25 years, so to discover these undescribed species highlights how much work is still to be done on sorting out the taxonomy of Australian fishes.”