When Genetics and Geology Meet in Patagonia

Released: 8-Apr-2008 10:20 AM EDT
Source Newsroom: Dalhousie University
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Newswise — When Charles Darwin first set foot on Patagonia, he was a fresh-faced 22-year old yet to finesse his revolutionary theory of evolution by natural selection.

But traveling around the tip of South America aboard the HMS Beagle—part of an epic, five-year scientific expedition—the young naturalist had his eyes opened to the immense diversity of species and landscapes.

Now, almost two centuries later, a group of scientists from across disciplines and academic institutions in North and South America are revisiting places Darwin explored, and, like him, pondering the connections between the evolution of landscape and of organisms.

Daniel Ruzzante, Canada Research Chair in Marine Conservation Genetics, and Sandra Walde, professor of population and evolutionary ecology, both with Dalhousie's Biology department, together with colleagues at the Universidad de Concepción in Chile and Universidad del Comahue in Argentina, have used molecular genetics to explore historic patterns of population crashes and explosions of two native species of Patagonian fishes. Explaining these patterns however, required an understanding of the evolution of landscape in the Andes.

Enter John Gosse, a Canada Research Chair in Earth Systems Evolution. The Earth Sciences professor uses digital terrain models and isotope geochemistry methods to map and date events that changed the landscape. His research often takes him to the southern Andes.

The group's recent paper, Climate control on ancestral population dynamics, has just been published in Molecular Ecology. Presenting one of the most comprehensive phylogeographic studies yet conducted in South America, the paper argues observed changes in freshwater fish demographics occurred in response to climate change over the past three million years. (Phylogeography is the study of historical processes that may be responsible for the contemporary geographic distributions of populations.)

One of the species, Galaxias platei, gradually rebounded after its population was squeezed 23,000 to 25,000 years ago, a time which coincides with the last ice age when ice extended over southern South America. In comparison, the more widely distributed and adaptable Percichthys trucha showed continuous growth, even through the last two ice ages.

Historic climate change resulted in "genetic bottlenecks," followed by dramatic expansion and growth of the aquatic fauna of the region, leading to the geographical rearrangement of both species and genetic diversity. This type of evidence for climate controls on the Earth's fauna is an example of the kinds of breakthroughs that reaching across traditional boundaries between disciplines can yield.

"Patagonia is like nowhere else in the world. And the research we are doing there is all brand new stuff and this is that's what makes it so exciting," says Dalhousie PhD student Tyler Zemlak, who was recently in Patagonia for a fieldtrip funded by the National Geographic Society.

Now aquatic species and their habitats in Patagonia are facing different threats. There's global warming, which is thinning the ice of mountain glaciers at an alarming rate. And, there's competition from invasive species, including Atlantic salmon, several species of Pacific salmon, rainbow trout, brook trout and lake trout and brown trout, all northern hemisphere species native to North America or Europe.

"Many of these species, like Atlantic salmon and the various Pacific salmon species, are escapees from fish farms," explains Dr. Ruzzante, originally from Argentina. "Now out in the wild, they're competing with, and in some cases feeding on, native species."


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