By its very nature, evolution is a long drawn out process. While it can be easily observed in the lab using organisms with short generation times like bacteria and fruit flies, seeing it happen in the wild with animals that live for much longer is far trickier.
But by using a long-term study of one population of penguins, researchers have been able to do just this, documenting natural selection acting on the birds, something which has only been achieved for a bird species once before.
“We know that evolution occurs – that species change,” explained the University of Washington’s Dee Boersma, co-author of the study published in the journal The Auk. “But to see this process in long-lived animals you have to look at generations of individuals, track how traits are inherited and detect selection at work.”
Boersma has been focusing on a single colony of Magellanic penguins in South America, spending 34 years documenting their lifespan, reproduction, and behavior.
Found along the coast on the tip of South America, the Magellanic penguin (Spheniscus magellanicus) nest in large colonies of up 500,000 individuals. But it’s their tendency to stick with one partner during breeding season, and return to the same beach each year that means Boersma has been able to follow individual birds over a period of decades, tracking their physical characteristics as well as keeping detailed notes on their offspring and their looks.
The penguins of the Punta Tombo colongy, Argentina. Dee Boersma
By doing this, Boersma has been able to build up a vastly detailed picture of the birds in the Punta Tombo colony in Argentina, and how certain traits have changed over time. “We chose characteristics that might be important to the success of individual penguins, like body size and bill depth,” said Boersma. “And once we had generations of trackable data for individuals and their descendants, we could ask: do these traits change over time?”
For this latest study, the researchers trawled through 28 years of Boersma’s data, from which they were able to detect natural selection occurring in seven of the years for both sexes. While selection is no doubt happening every year, they found that the variable condition where the penguins live mean that is difficult to determine which direction it is pushing them.
From these seven years that could use, however, they were able to see clear signs that larger males had better reproductive success in years when fish stocks were low, while natural selection was influencing the foot size, bill depth, and body size of the females, though they were unable to determine exactly why.
“This is the first decades-long study to measure selection in penguins, and only the second one for birds overall,” said Laura Koehn, another of the study’s authors. They hope that as the study continues over the years, more data will help them pick up the exact causes for these and other traits.
At its height, there were 500,000 penguins nesting. Dee Boersma
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