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Stickleback fish provide new insight into natural selection

Many animals will not be able to survive climate change, and predicting how individual species will respond can be very challenging. In a new study from McGill University, scientists have used genome sequencing to reveal that some animals, like the threespine stickleback fish, can adapt remarkably quickly to extreme new environments. 

According to the researchers, the findings could help scientists forecast the evolutionary future of stickleback populations.

Threespine stickleback fish are known to be very resilient. They can live in both seawater and freshwater, and under a wide range of temperatures. The researchers set out to investigate the genetic foundation of such adaptations.

“The modern version of Darwin’s idea of evolution by natural selection posits that organisms with genes that favor survival and reproduction will tend to leave more offspring than their peers, causing the genes to increase in frequency over generations. As a result, populations become adapted or better-suited to their environments over time,” explained study lead author Alan Garcia-Elfring.

“However, this process has typically been studied retrospectively, in populations that adapted to their current environments long in the past. This can make it difficult to understand the sequence of events – for example, which traits were most important and when – that led to their adaptation.”

To study natural selection among threespine stickleback fish, the experts tracked six populations before and after seasonal changes to their environment through genome sequencing. 

In estuaries along the coast of California, dramatic seasonal shifts take place that range from wet winters to dry summers. The habitat structure changes, as well as the balance of saltwater and freshwater, which means that fish must rapidly adapt to survive from season to season. 

For example, when sandbars form during dry summer months, estuaries become temporarily shut off from the ocean. Such conditions present a unique opportunity for experts to study natural selection in real time.

“These changes probably resemble the habitat shifts experienced by stickleback populations when they colonized many newly created freshwater lakes from the ocean after the glaciers receded 10,000 years ago” said Professor Barrett. “We hope to gain insight into the genetic changes that may have resulted from natural selection long in the past.”

The researchers discovered genetic changes in the stickleback fish driven by seasonal shifts in habitat that were comparable to differences found between long-established freshwater and saltwater populations. 

“These genetic changes occurred in independent populations over a single season, highlighting just how quickly the effects of natural selection can be detected,” said Alan Garcia-Elfring.

“The findings are important because they suggest that we may be able to use the genetic differences that evolved in the past as a way to predict how populations may adapt to environmental stressors like climate change in the future.”

The research highlights the importance of studying species that adapt to dynamic environments to gain a better understanding of how natural selection works. 

The study is published in the journal Molecular Ecology.

By Chrissy Sexton, Staff Writer

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