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Penguins Survived in Three Refugia during Ice Age

A study of how changing climate has affected emperor penguins over the past 30,000 years has found that only three populations may have survived during the last ice age, and that the Ross Sea was likely the refuge for one of these populations.

Scientists from the universities of Tasmania, Southampton, Oxford and the Australian Antarctic Division examined the genetic diversity of modern and ancient emperor penguin populations in Antarctica to estimate how they had been changing over time.

Emperor penguins breed on sea-ice during the Antarctic winter, when temperatures regularly drop below –30°C. However, conditions were too harsh even for emperor penguins during the last ice age, with the study of genetic diversity finding that the population then was roughly seven times smaller than today and split into three refugial populations.

Emperor penguin numbers only increased over the past 12,000 years as sea-ice decreased around Antarctica throughout the Holocene warming period. This finding suggests that current sea-ice conditions may be optimal for emperor penguins.

The research, published in Global Change Biology, found that emperor penguin colonies spanning 8000 km of coastline are interbreeding, suggesting that they migrate much farther around Antarctica than previously thought. This has important implications for forecasting studies that have so far considered breeding colonies as isolated units.

“Due to there being about twice as much sea-ice compared to current conditions, the penguins were unable to breed in more than 2a few locations around Antarctica,” said the study’s co-leader, Jane Younger, a PhD student at the University of Tasmania’s Institute for Marine and Antarctic Studies. “The distances from the open ocean, where the penguins feed, to the stable sea-ice where they breed was probably too far. The three populations that did manage to survive may have done so by breeding near polynyas – areas of ocean that are kept free of sea-ice by wind and currents.”

One of the polynyas that supported a population of emperor penguins throughout the last ice age was probably in the Ross Sea. Emperor penguins that breed in the Ross Sea today are genetically distinct from other emperor penguins around Antarctica, which suggests they became isolated during the last ice age.

University of Tasmania project leader, Dr Karen Miller, said emperor penguins in the Ross Sea do not interbreed with penguins from elsewhere. This is puzzling as there are no clear barriers isolating the Ross Sea colonies.

“The projected rate of temperature increase over the next century is an order of magnitude greater than that during the early Holocene,” Miller said. “Whether the resilience demonstrated in the past by emperor penguins will enable them to adapt to projected climate change remains to be seen, as rising temperatures will alter their habitat far more rapidly than in the past.”