Penguins are no strangers to climate change. Their life history has been shaped by rising and falling temperatures, and their bodies are adapted to Earth’s most extreme conditions.
Yet scientists are concerned that the evolutionary path of penguins could reach a dead end due to what appears to be the slowest rate of evolution ever found in birds.
A team of international researchers has just published one of the most comprehensive studies of penguin evolution to date, combining data from living and fossil penguin species for the first time.
The study reveals the turbulent life history of penguins in general: Three-quarters of all known penguin species, currently represented only by fossils, are already extinct.
“Over 60 million years, these iconic birds have evolved into highly specialized marine predators and are now well adapted to some of the most extreme environments on Earth,” the authors write.
“However, as their evolutionary history shows, they now stand as sentinels, highlighting the vulnerability of cold-adapted fauna in a rapidly warming world.”
On land, penguins can seem a little silly, with their clumsy gaits and seemingly useless wings. But underwater, their bodies turn into hydrodynamic torpedoes that will make any escaping fish dream of flying.
Penguins had already lost their ability to fly 60 million years ago, before the formation of the polar ice sheets, in favor of wing diving.
Fossils and genomic evidence suggest that the unique features that enabled penguins to be aquatic evolved early in their existence as a group, with the rate of evolutionary change generally slowing down over time.
Scientists believe penguins originated on the Gondwanan microcontinent called Zealand, which is now mostly submerged under the ocean.
The paper suggests that the ancestors of modern penguins – the crown penguins – appeared about 14 million years ago, a full 10 million years after genetic analysis hinted at it.
This particular period would coincide with the moment of global cooling, called the Middle Miocene climate transition. However, living penguins have split into distinct genetic groups over the past 3 million years.
The penguins dispersed across Zealand before dispersing several times into South America and Antarctica, and later groups probably caught the Antarctic Circumpolar Current.
Scientists have found that almost every species of penguin experienced a period of physical isolation during the last ice age.
Their contact with other penguins during this time was limited as the groups were forced to live in more fragmented areas of habitat further north where they could still find food and shelter.
As a result, each group’s DNA pool became narrower, genetically pushing the species apart.
In the subsequent warming period, they moved back to the poles, and some groups, now much more genetically distinct, crossed again.
How certain groups of penguins have survived these significant climate events provides insight into how they can cope with anthropogenic climate change.
The groups that increased in numbers when the warming happened had some things in common: they were migratory and foraged offshore. The researchers believe that these features allowed them to better respond to climate change, especially the ability to search for prey from afar and move to lower latitudes.
On the other hand, those who have declined in numbers lived in one particular place and foraged closer to the coast: a way of life that does not adapt too well when “home” conditions change dramatically.
But the ability of penguins to change may not only be limited by lifestyle – it seems to be in their genes.
It turned out that penguins have the lowest evolutionary rates ever found among bird species, along with their sister order Procellariiformes, which includes birds such as petrels and albatrosses.
The researchers compared a total of 17 different orders of birds using several genetic signatures closely related to the rate of evolutionary change.
They noticed that aquatic birds tend to have slower evolutionary rates than their terrestrial counterparts, so they think the transition to aquatic life may go hand in hand with slower evolutionary rates. They also believe that the rate of bird evolution is slower in cooler climates.
The order Pelecaniformes, which includes seabirds such as pelicans and cormorants, had almost the third lowest rate of evolution, and waterfowl (order Anseriformes) had a much lower rate than land birds such as turkeys, chickens, and quails. (order Galliformes).
The researchers note that crown penguin ancestors evolved faster than modern penguins, but even then it was slower compared to other birds.
Half of all living penguin species are endangered or vulnerable, and scientists say their slow pace of evolution and niche lifestyle could put penguins in a dead end.
“The current rate of warming, combined with limited refuges in the Southern Ocean, is likely to far exceed the adaptive capacity of penguins,” they write.
“Risks of future collapses are always present as penguin populations in the Southern Hemisphere face rapid anthropogenic climate change.”
This study was published in Connection with nature.
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