Sliding down snowy Antarctic slopes and zipping through frigid waters, penguins seem perfectly suited to their environment. But the charismatic birds weren’t always flightless aquatic acrobats: Evolving from flying to swimming demanded an almost entirely new set of skills, body shapes, and functions.
“Penguins are evolution’s most entertaining product,” says study co-author Daniel Ksepka, an avian paleontologist at the Bruce Museum in Greenwich, Connecticut. “They’ve adapted an entirely different body plan and lifestyle than their ancestors.”
The study, published today in the journal Nature Communications, shows early penguins were surprisingly quick to adapt to newly created environmental niches throughout the Southern Hemisphere in the wake of the Cretaceous-Paleogene mass extinction around 66 million years ago. After dinosaurs disappeared, there was more room for other animals to spread, and penguins filled in different climates and biomes around the southern half of the world.
But the research also reveals that penguins exhibit the slowest known rate of evolution among all birds, meaning their rate of genetic mutations has slowed significantly since their switch to marine life following the mass extinction. That throws into question their ability to rapidly adapt to the breakneck pace of modern climate change, the study authors say.
Over half of the about 18 living penguin species, which dwell in places as diverse as Brazil, New Zealand, and South Africa, are already recognized as endangered or vulnerable by the International Union for Conservation of Nature.
“Modern penguins seem to be less well equipped to survive these rapid environmental changes than ancient penguins because of this decrease in evolutionary rate,” says Vanesa De Pietri, an avian paleontologist at New Zealand’s University of Canterbury who was not involved in the study. (Read about seven species hit hard by climate change.)
“Have they specialized themselves into a corner?” she asks. “Yeah, probably.”
The direct ancestor of penguins is still unknown due to a lack of fossils, says De Pietri. The mysterious descendant probably lived over 60 million years ago, when it diverged from related groups of flying birds resembling albatrosses and petrels.
Previous research into penguin evolution has also been limited by the fact that about three-quarters of all penguin species are extinct, known only through the fossil record. Until now, no studies have combined the complete fossil record with all modern and recently extinct penguin genomes.
“This is an impressive approach to understanding penguin evolution,” says Nic Rawlence, a paleogeneticist at New Zealand’s University of Otago who was not involved in the study. (See beautiful photos of penguins.)
By bringing these two massive datasets together, the team—including co-author Pablo Borboroglu, a marine biologist and National Geographic Explorer—refined penguins’ evolutionary tree, pinpointed times when penguins became more diverse, charted changes in populations, and determined which genes helped penguins make the transition to the life aquatic.
“It really gives us the whole picture,” says Ksepka.
The analysis of the penguins’ genomes showed how the birds came to have rigid flippers and waterproof feathers for swimming, thick skin and fat to keep warm, and underwater vision and oxygen control for diving.
Scientists already knew about these adaptations, but comparing all extant penguins’ genomes allowed the team to identify the genes responsible for them. Tying the genomes to the fossil record also produced estimates as to when the genes, and different species, appeared. The last step was connecting it all to climate.
Keeping up with climate change
After their initial burst of adaptation, penguins’ evolutionary rate gradually slowed down. (Woodpeckers have one of the fastest rates, though the reason remains a mystery.)
Having evolved for marine environments, penguins then had to adjust to repeated climate swings over millions of years. A new burst of penguin species diversification started just over two million years ago, when the most recent glacial period began. As ice sheets grew and environments changed, penguins migrated and were often cut off from other groups entirely. Over hundreds of thousands of years, separated by the ice, penguins evolved into the diverse array of penguin species alive today.
While previous research has hypothesized this process, the new genomic-fossil data combination offers the strongest evidence yet for it.
“This study has shown really nicely, in a genomic context, how diversification events can be correlated with major climatic events throughout the history of penguins,” says De Pietri.
A bleak future?
Many penguins adapted to previous climate swings with ease. But the rate of climate change today—at a magnitude more rapid than the shifts penguins previously survived—presents penguins with a novel evolutionary challenge. It’s one the study authors think penguins are unlikely to meet.
“Many penguins are living in ground zero areas for climate change,” says Ksepka. Antarctic species, such as the chinstrap penguin, are especially at risk; the continent has lost roughly three trillion tons of ice since the early 1990s. Penguins restricted to islands are also vulnerable, since they “have nowhere to go,” Ksepka says.
“I think the fate of penguins is tied up in the fate of humanity, really.”