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 worry that the penguin’s evolutionary trajectory may be stalling, 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, the first to integrate data from living and fossil penguin species.
The research reveals 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 to become highly specialized marine predators, and are now well adapted to some of the most extreme environments on Earth,” the authors write.
“Yet, as their evolutionary history reveals, they now stand as sentinels highlighting the vulnerability of cold-adapted fauna in a rapidly warming world.”
On land, penguins can appear a bit ridiculous, with their awkward waddling and seemingly useless wings. But underwater, their bodies are transformed into hydrodynamic torpedoes that make any fleeing fish wish they could fly.
Penguins had already lost the ability to fly 60 million years ago, before the formation of polar ice sheets, in favor of wing-powered diving.
The fossils and genomic data suggest that the unique traits that enable penguins’ aquatic lifestyle emerged early in their existence as a group, with rates of evolutionary change generally trending downward over time.
The researchers believe penguins originated on a Gondwanan microcontinent called Zealandia, which is now largely submerged under the sea.
The paper suggests that the ancestors of modern penguins – crown penguins – appeared about 14 million years ago, a full 10 million years after genetic analyzes have suggested.
This particular period would coincide with a moment of global cooling called the mid-Miocene climate transition. However, living penguins have split into separate genetic groups over the past 3 million years.
Penguins spread across Zealandia before dispersing to South America and Antarctica several times, with later groups likely traveling on the Antarctic Circumpolar Current.
The researchers 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 areas of habitat further north, where they could still find food and shelter.
As a result, the DNA pool of each group narrowed, pushing species further apart genetically.
In the warming period that followed, they moved back toward the poles, and some groups, now much more genetically distinct, crossed paths again.
The way certain groups of penguins experienced these important climate events provides insight into how they might cope with anthropogenic climate change.
The groups that increased in number when the warming occurred shared some traits: They were migratory and foraging offshore. The researchers believe that these features enabled them to better respond to changing climates, particularly the ability to look further afield for prey and move to lower latitudes.
Those who decreased in number, on the other hand, lived in one particular place, and searched closer to land for food: a lifestyle that does not cope well when conditions “at home” change drastically.
But penguins’ ability to change may be limited by more than just lifestyle — it appears to be built into their genes.
It turns out that penguins have the lowest rates of evolution yet discovered in avian species, along with their sister order, the Procellariiformes, which includes birds such as petrels and albatrosses.
The researchers compared a total of 17 different orders of birds, using several genetic signatures that are closely related to rates of evolutionary change.
They noticed that aquatic birds generally had slower evolutionary rates than their terrestrial relatives, so they believe that the adoption of an aquatic lifestyle may go hand in hand with slow evolutionary rates. They also believe that development rates in birds are lower in cooler climates.
The order Pelecaniformes, which includes seafaring birds such as pelicans and cormorants, was a nearly third for the lowest rate of evolution, and waterfowl (order Anseriformes) had much lower rates than land-bound birds such as turkeys, chickens and quail (order Galliformes).
The researchers note that ancestral crested penguins evolved faster than living penguins, but even then this 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 toward a dead end.
“The current rate of warming combined with limited refugia in the Southern Ocean is likely to far exceed the adaptive capacity of penguins,” they write.
“The risk of future collapses is ever-present as penguin populations across the Southern Hemisphere face rapid anthropogenic climate change.”
This research was published in Nature communication.