Penguins are no strangers to climate change. Their life history has been shaped by rising and falling temperatures, and their bodies are highly specialized for some of Earth’s most extreme conditions.
And yet, scientists fear the penguin’s evolutionary pathway may come to a halt, thanks to what appear to be the lowest rates of evolution ever detected in birds.
A team of international researchers has just published one of the most comprehensive studies of penguin evolution to date, which is the first to integrate data from living and fossil penguin species.
The research unravels the tumultuous life history of penguins in general, with three quarters of all known penguin species – now represented only by fossils – already extinct.
“Over 60 million years, these iconic birds have evolved into highly specialized marine predators and are now well adapted to some of Earth’s most extreme environments,” the authors write.
“Yet, as their evolutionary history reveals, they now stand as sentinels highlighting the vulnerability of cold-adapted wildlife in a rapidly warming world.”
On land, penguins can look a little silly, with their clumsy waddling and seemingly useless wings. But underwater, their bodies transform into hydrodynamic torpedoes that any runaway fish would dream of.
Penguins had already lost their ability to fly 60 million years ago, before the formation of the polar ice caps, in favor of wing-powered diving.
Fossils and genomic data suggest the unique features that allow penguins’ aquatic lifestyles to emerge early in their existence as a group, with rates of evolutionary change generally trending downward over time.
Scientists believe penguins originated on a Gondwana micro-continent called Zealandia, which is now mostly submerged under the ocean.
The article suggests that the ancestors of modern penguins – king penguins – appeared about 14 million years ago, or 10 million years after genetic analyzes suggested.
This particular period would coincide with a moment of global cooling called the Middle Miocene climate transition. Living penguins, however, have split into distinct genetic groups over the past 3 million years.
The penguins dispersed across Zealandia before dispersing several times to South America and Antarctica, with later groups likely hitching a ride on the Antarctic Circumpolar Current.
Scientists have found that almost all penguin species experienced a period of physical isolation during the last Ice Age.
Their contact with other penguins was limited during this time, as groups were forced to live in more fragmented habitat areas farther north where they could still find food and shelter.
As a result, each group’s DNA pool became narrower, genetically distancing the species.
In the ensuing period of warming, they moved back towards the poles, and some groups, now much more genetically distinct, interbred again.
How certain groups of penguins experienced these significant climatic events provides insight into how they might cope with human-induced climate change.
The groups that increased in number during the warming shared certain characteristics: they were migratory and fed offshore. The researchers believe that these characteristics allowed them to better respond to climate change, in particular the ability to seek prey farther and move to lower latitudes.
Those that dwindled in number, on the other hand, lived in a particular location and sought food closer to shore: a way of life that doesn’t adapt very well when conditions “at home” change drastically.
But penguins’ ability to change might be limited by more than just lifestyle – it seems to be ingrained in their genes.
It turns out that penguins have the lowest evolutionary rates ever detected among bird species, along with their sister order Procellariiformes, which includes birds like petrels and albatrosses.
The researchers compared 17 different orders of birds in total, using several genetic signatures closely linked to rates of evolutionary change.
They noticed that waterfowl generally had slower rates of evolution than their terrestrial relatives, so they speculate that adopting an aquatic lifestyle might go hand in hand with low rates of evolution. They also believe that rates of evolution in birds are lower in cooler climates.
The order Pelecaniformes, which includes seabirds like pelicans and cormorants, was nearly a third for the lowest rate of evolution, and waterfowl (order Anseriformes) had much lower rates than landbirds. such as turkeys, chickens and quail (order Galliformes).
Researchers note that ancestral crown penguins evolved at a faster rate than living penguins, but even then it was slow compared to other birds.
Half of all living penguin species are endangered or vulnerable, and scientists say their slow evolutionary rates and niche lifestyles could send penguins into a bind.
“The current rate of warming combined with limited refuges in the Southern Ocean will likely far exceed the penguins’ ability to adapt,” they write.
“The risks of future collapses are ever-present as Southern Hemisphere penguin populations face rapid anthropogenic climate change.”
This research was published in Nature Communication.