How the penguins beat the heat and headed south

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

With all of these adaptations to cold weather, it’s hard to imagine penguins living anywhere else. But fossils of ancient penguins have appeared along the equator, and many of these prehistoric seabirds predate the formation of the Antarctic 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 environment.”

To determine how penguins moved from fresh, tropical waters to polar seas, Dr Ksepka and his colleagues recently analyzed the genomes of all living penguins, including pipsqueaks like the blue penguin, rarities like the yellow-eyed penguin endangered species and stars such as the yellow-tufted rockhopper penguin. However, the genetics of modern penguins could not tell researchers 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 extinct now”. He added: “You have to consult the fossil record, otherwise you will only get a fragment of the story.”

To supplement the modern data, the researchers examined the fossils of a motley crew of ancient sailors. Some prehistoric penguins roamed the tropical waters off Peru, using spear-like beaks to spear fish. Others sported long legs, and the tallest might have grown seven feet tall. Some even had spots of rusty red feathers.

Comparing the genomes of modern penguins with fossil penguins allowed the team to piece together the evolution of penguins. In their findings, published Tuesday in Nature Communications, the researchers identified genes that helped penguins transition from wading in warm waters to perfecting polar diving. Some of these genes helped the penguins pack on fat, while others turned their shrunken wings into streamlined fins. Some have even boosted penguins’ immune systems or helped them tolerate low oxygen during deep dives.

The researchers also identified genes that helped fine-tune the penguins’ eyes for looking through the icy depths. While most birds have four colored cones in their eyes, one of them is inactive in penguins, hampering their ability to see green and red. Instead, their eyes adapted to match the ambient blue of the ocean.

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

When these changes happened to the ancient penguins, they stuck. Genetic analyzes have revealed that penguins generally have the lowest rate of evolution of all bird groups. Because they look so bizarre, this rate of glacial change seems surprising. But it does reveal just how successful the penguin’s plump but streamlined body plan is – over millions of years it has changed only in slow increments. But emperor penguins, which breed in Antarctica’s harsh winter, have the highest rate of evolution of any penguin, leading researchers to infer that colder temperatures somehow accelerate or another the evolution of penguins.

Juliana Vianna, an ecologist at the Pontifical Catholic University of Chile, says this idea is consistent with the southward march of penguins that occurs during episodes of global cooling. “Their evolutionary history is roughly associated with historic climate change and glaciation,” said Dr. Vianna, who recently conducted similar research but was not involved in the new study.

Understanding how penguins have changed in the past may offer clues as to how these cold weather specialists might fare in a warmer future. “Warming temperatures will impact the biogeographical ranges of penguins, the species they depend on for food and the species that in turn hunt them,” said Daniel Thomas, a palaeontologist from Massey University in New Zealand. and author of the new study.

While the research is a comprehensive overview of the penguin family, Dr Ksepka said, one seabird is still missing – the last flying penguin. The little puffin-like bird likely lived in ancient New Zealand, but its fossils have proven elusive. “That would be the first thing I would ask if I had a genie,” he said.

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