How the Penguins Beat the Heat and Go South

Few animals have evolved to survive in the unforgiving Antarctica like penguins. Species such as the emperor penguin have overlapping layers of insulating feathers, tight blood vessels to recycle body heat, and a stomach sufficient to withstand wind chills approaching minus 80 degrees Fahrenheit.

With all these cold weather adaptations, it’s hard to imagine penguins living anywhere else. But ancient penguin fossils have emerged along the Equator, and many of these prehistoric seabirds predate the formation of the Antarctic ice sheet. “They lived through some of the hottest times in Earth’s history, when it was five degrees warmer at the Equator,” said Daniel Ksepka, a paleontologist at the Bruce Museum in Greenwich, Conn. “They basically evolved in an ice-free context. ”

To determine how penguins transition from comfortable tropical waters to the polar seas, Dr. Ksepka and his colleagues recently analyzed the genomes of all living penguins, including pipsqueaks such as the foot-high blue penguin, rarities such as the endangered yellow-eyed penguin and showstoppers such as the yellow tufted rockhopper penguin. However, modern penguin genetics can only tell researchers. Most modern lineages date back only a few million years, obscuring much of the penguin’s 60 million year evolutionary journey.

Dr. Ksepka said that more than three-quarters of penguin species are “extinct now”. He added, “You have to look at the fossil record, or you only get part of the story.”

To complement the modern data, the researchers examined fossils from a diverse crew of ancient sailors. Several prehistoric penguins waded through the tropical waters of Peru, using their spear-like beak to catch fish. Others wear long legs, and the largest may have pushed up to seven feet. Some even have patches of rusty red fur.

Comparing modern penguin genomes with fossil penguins allowed the team to reconstruct penguin evolution. In their findings, published Tuesday in Nature Communications, the researchers pinpoint a gene that helps penguins transition from wading through warm waters to perfecting polar plunge. Some of these genes help penguins’ ability to pack fat, while others shape their shriveled wings into slender fins. Some even strengthen penguins’ immune systems or help them tolerate low oxygen during deep dives.

The researchers also identified a gene that helps perfect the penguin’s eyes for peering through the depths of the ice. While most birds have four color cones in their eyes, one of them is inactive in penguins, hindering their ability to see green and red. Instead, their eyes have adapted to adjust to the blue of the ocean.

Some of the missing genes baffled researchers. While modern penguins devour krill, the team found evidence that their ancestors did not have genes that would help break down crustacean shells. This may be evidence that ancient penguins speared larger prey, such as fish and squid. Penguins maintain a limited palate. Their taste receptors can only pick up on salty and sour tastes, which is “pretty good if you eat fish,” says Dr. Ksepka. “Maybe that’s why they’re quite happy with sardines.”

When this change occurred in ancient penguins, they were trapped. Genetic analysis revealed that penguins generally had the lowest evolutionary rate of any group of birds. Because they look so strange, the rate of this glacial change seems surprising. But it does reveal how successful the penguin’s curvaceous yet slender body plan has been—over millions of years, it’s only changed gradually. But emperor penguins, which breed during bitter Antarctic winters, have the highest evolutionary rate of all penguins, leading researchers to conclude that colder temperatures have somehow accelerated penguin evolution.

Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, said the idea was consistent with the southward movement of penguins that occurred during the bout of global cooling. “Their evolutionary history is pretty much tied to climate change and historical glaciation,” said Dr. Vianna, who recently led similar research but was not involved in the new study.

Understanding how penguins have changed in the past can provide clues as to how these cold-weather specialists might survive a hotter future. “Warming temperatures will have an impact on the biogeographical ranges of penguins, the species they rely on for food and the species that, in turn, hunt them,” said Daniel Thomas, a paleontologist from Massey University in New Zealand and author of the new study.

While this study is a comprehensive review of the penguin family, Dr. Ksepka said there was still one seabird missing — the last flying penguin. The little puffin-like bird may have lived in ancient New Zealand, but its fossils are proving elusive. “That would be the No. 1 thing I would ask for if I had a genie,” he said.

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