Penguins are no stranger to climate change. Their life history has been shaped by rising and falling temperatures, and their bodies are highly specialized in some of the harshest conditions on Earth.
However, scientists are concerned that the penguin’s evolutionary path may be halted, thanks to what appear to be the lowest evolutionary rates 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 combine data from living and fossil penguin species.
The research reveals the turbulent life history of penguins in general, with three-quarters of all known penguin species – now represented only by fossils – having already become extinct.
Over the course of 60 million years, these distinctive birds have evolved into highly specialized marine predators, and are now well-adapted to some of the harshest environments on Earth,” the authors wrote.
“However, as their evolutionary history reveals, they now stand as sentinels highlighting the vulnerability of cold-adapted animals in a rapidly warming world.”
On land, penguins can look a little silly, with their awkward trembling and seemingly useless wings. But under the water, their bodies transform into hydrodynamic torpedoes that would make any escaping fish wish they could fly.
Penguins actually lost their ability to fly 60 million years ago, before the formation of the polar ice sheets, in favor of two-wing diving.
Fossils and genomic data point to the unique features that enable penguins to emerge from aquatic lifestyles early in their existence as a group, with rates of evolutionary change generally trending downward over time.
Scientists believe that the penguins originated on the small continent of Gondwan called Zealandia, which is now mostly submerged under the ocean.
The research paper notes that the ancestors of modern penguins – the coronal penguins – appeared approximately 14 million years ago, a full 10 million years after hinting at genetic analyzes.
This particular period coincides with a moment of global cooling called the Middle Miocene climatic transition. However, living penguins have split into separate genetic groups over the past three million years.
The penguins spread throughout Zealand before spreading to South America and Antarctica several times, with later groups likely to trek up the Antarctic Current.
Scientists have found that nearly every species of penguin experienced a period of physical isolation during the last Ice Age.
Their contact with other penguins was limited during this time, as the groups were forced to live in more fragmented areas of habitat to the north, where they could still find food and shelter.
As a result, the DNA pool for each group became narrower, resulting in the genetically divergent species.
In the warming that followed, they returned to the poles, and some groups, now more genetically distinct, crossed paths again.
The way certain groups of penguins have experienced these important climate events offers insight into how they are dealing with human-caused climate change.
Groups that increased in number when warming occurred shared some features: they were migratory, and they fed outside. Researchers believe that these features allowed them to better respond to changing climates, especially the ability to look away from prey and move to lower latitudes.
On the other hand, those whose number had decreased lived in a certain place, and were looking for food near the shore: a lifestyle that does not adapt well when conditions “at home” radically change.
But penguins’ ability to change may be limited by more than just lifestyle – it seems to be embedded in their genes.
It turns out that penguins have the lowest evolutionary rates yet discovered in bird species, along with their sister, Procellariiformes, which includes birds such as petrels and albatrosses.
The researchers compared 17 different orders of birds overall, using several genetic signatures that are closely linked to rates of evolutionary change.
They note that waterfowl in general have slower rates of evolution than their terrestrial relatives, so they believe that adopting an aquatic lifestyle may go hand in hand with lower evolutionary rates. They also believe that rates of evolution in birds are lower in colder climates.
The order Pelicans, which includes seabirds such as pelicans and cormorants, was at about one-third of the lowest evolutionary rate, and waterfowl (order Anseriformes) had much lower rates than terrestrial birds such as turkeys, chickens, and quails (order Galliformes).
The researchers noted that ancestral coronal penguins evolved at a faster rate than living penguins, but even then, this was slow compared to other birds.
Half of all living penguin species are endangered or endangered, and scientists say their slow development rates and specialized lifestyles could send penguins toward a standstill.
“The current pace of warming combined with the limited sanctuary in the Southern Ocean is likely to far exceed the adaptive capacity of penguins,” they wrote.
“Future avalanche risks are constantly present as penguin populations across the Southern Hemisphere face rapid man-made climate change.”
This research was published in Nature Connections.
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