By Sarah-Jane O'Connor 15/12/2015

The diverse range of native fish in the South Island are thanks to the uplift of the Southern Alps, new research suggests.

Research published today in Nature Geoscience, and led by the University of Otago, has drawn a link between rapid mountain-building in the South Island and the diversification of native fish. 

Changes in geography have long been considered a driver of evolution, especially when barriers are formed that prevent reproduction across a range. But there are few clear examples of such an effect, especially because there are many other environmental and ecological factors at play.

University of Otago professors Dave Craw (Geology) and Jon Waters (Zoology) collaborated on the research which used a mathematical model to reconstruct the topographical evolution of the South Island over the past 25 million years.

The Marsden-funded research found the island’s landscape was separated into six main tectonic zones, each with distinct river drainage catchments. The zones separated roughly around Southland, Otago, Marlborough, Canterbury, the Southern Alps and the Australian Plate (West Coast plus Nelson/Tasman).

When the tectonic model was compared to a biological evolutionary tree – with over 1000 freshwater fish samples from more than 400 locations – fish DNA sequences diverged over time in tandem with the growth of the mountains. Mudfish, upland bully and several species of galaxiid were included in the model.

Professor Craw said the South Island was an ideal location to study how geology could shape biology, with both the landscape and its native species exhibiting rapid changes.

“By modelling the mountain-building processes, we can really start to understand how the changing landscape has shaped biological processes. New Zealand’s geographic isolation and dynamic geology make it the perfect place for understanding evolution.”

Professor Waters said he and Professor Craw had been collaborating for about 15 years and found a lot of common ground between their two disciplines.

“One particularly interesting thing about the study, from a biological point of view, is that we find such similar evolutionary patterns in unrelated groups of fish species, which really highlights the important role of geology,” he said.

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Featured image: Flickr CC, Aoraki/Mt Cook, Tristan Schmurr.