How penguins beat the heat and headed south

Few animals have evolved to survive the unforgiving Antarctic like penguins. Species like the emperor penguin have overlapping layers of insulating plumage, tightly packed veins to recycle body heat, and just enough belly to survive wind chills that approach minus 80 degrees Fahrenheit.

With all these adaptations to cold weather, it’s hard to imagine penguins living anywhere else. However, fossils of ancient penguins have surfaced along the equator, and many of these prehistoric seabirds predate Antarctica’s ice sheets. “They experienced 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, Connecticut. “They basically evolved in an ice-free context. ”

To determine how penguins migrated from mild, tropical waters to polar seas, Drs. Ksepka and his colleagues recently analyzed the genomes of all living penguins, including tiny ones like the foot-sized blue penguin, rarities like the endangered yellow-eyed penguin, and showstoppers like the yellow-tufted rockhopper penguin. However, the genetics of modern penguins could only tell researchers so much. Most modern lineages date back only a few million years, obscuring most of the 60-million-year odyssey of penguin evolution.

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

To supplement the modern data, the researchers examined fossils from a ragtag crew of ancient seafarers. Some prehistoric penguins swam in tropical waters off Peru and used spear-like beaks to harpoon fish. Others had long legs, and the tallest was perhaps two meters tall. Some even had spots of rusty red feathers.

By comparing the genomes of modern penguins with fossil penguins, the team was able to reconstruct the evolution of penguins. In their findings, published Tuesday in Nature Communications, the researchers located genes that helped penguins transition from wading through warm waters to perfecting the polar jump. Some of these genes supported the penguins’ ability to pack fat, while others shaped their shriveled wings into streamlined fins. Some even boosted the penguins’ immune systems or helped them tolerate low oxygen during deep dives.

The researchers also identified genes that helped fine-tune penguin eyes to see through icy depths. While most birds have four color cones in their eyes, penguins have one of them inactive, hindering their ability to see green and red. Instead, her eyes have adapted to the surrounding ocean blue.

Some missing genes puzzled the researchers. While modern penguins eat krill, the team found evidence their ancestors lacked genes that would have helped break down crustacean shells. This could be evidence that ancient penguins speared larger prey such as fish and squid. Penguins retain a restricted palate. Your taste receptors can only pick up salty and sour tastes, which “is pretty good if you’re eating fish,” said Dr. ksepka “That’s probably why they’re pretty happy with sardines.”

When these changes occurred in old penguins, they stuck. The genetic analyzes revealed that penguins generally have the lowest evolutionary rate of any bird group. Because they look so bizarre, this glacial rate of change seems surprising. But it shows how successful the penguin’s clumsy but streamlined body plan is – it’s changed at slow increments over millions of years. But emperor penguins, which breed during the bitter Antarctic winter, have the highest rate of evolution of any penguin, leading researchers to conclude that colder temperatures are somehow accelerating penguin evolution.

Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, says this idea is consistent with the southward migration of penguins that occurs during global cooling periods. “Their evolutionary history is quite closely linked to historical climate change and 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 could provide clues as to how these cold-weather specialists might fare in a hotter future. “Warming temperatures will affect the biogeographic ranges of penguins, the species they depend on for food, and the species they in turn prey on,” said Daniel Thomas, paleontologist at Massey University in New Zealand and author of the new study.

As the research takes a broad look at the penguin family, says Dr. Ksepka, one more seabird is missing – the last flying penguin. The small, puffin-like bird likely lived in ancient New Zealand, but its fossils have proven elusive. “That would be the number one thing I would ask for if I had a Genie in a bottle,” he said.

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