Penguins first appeared about 22 million years ago, not in Antarctica, as many scientists have thought, but in the cool coastal regions of Australia and New Zealand, according to new research.
An international team of scientists gathered blood and tissue samples from 22 penguins representing 18 species, then sequenced and analysed their whole genomes to chart movement and diversification over the millennia.
The evidence indicates, they say, that the ancestors of the king and emperor penguins, the two largest species, soon split off from the other penguins and moved to sub-Antarctic and Antarctic waters, respectively, presumably to take advantage of abundant food resources.
This is consistent with the contested hypothesis that these two penguins – the only species in the genus Aptenodytes – are the sister group to all other penguin lineages.
“It was very satisfying to be able to resolve the phylogeny, which has been debated for a long time,” says Rauri Bowie from the University of California, Berkeley, co-corresponding author of a paper in the journal Proceedings of the National Academy of Sciences.
The other penguins diversified and spread across the southern oceans after Drake’s Passage between Antarctica and the tip of South America fully opened about 12 million years ago.
Today, they are found in Australia and NZ (yellow-eyed, little and other crested penguins), Antarctica (emperor, Adélie, gentoo and chinstrap), the tropical west coast of South America (Galápagos and Humboldt), the southern coasts of South America (Magellanic and southern rockhopper), the South Atlantic (Magellanic and Macaroni), southern Africa (African) and some in the sub-Antarctic (king, gentoo and Macaroni), Indian Ocean islands (eastern rockhopper) and sub-tropical regions (northern rockhopper).
The research pinpointed genetic adaptions that allowed penguins to thrive in these new and challenging environments, including changes in genes responsible for regulating body temperature. There is a rider, however.
“[W]e want to make the point that it has taken millions of years for penguins to be able to occupy such diverse habitats, and at the rate that oceans are warming, penguins are not going to be able to adapt fast enough to keep up with changing climate,” Bowie says.
The project brought together scientists from the US, Chile, Brazil, Australia, Spain, the UK, France, Monaco, Norway and South Africa.
Using a range of techniques, some developed recently to analyse historical interactions among humans, Neanderthals and Denisovans, they were able to determine, they say, that several groups of penguins interbred over the course of their evolutionary history.
Through exchange of genetic material, penguins may have shared genetic traits that facilitated diversification across the steep thermal and salinity gradients encountered in the southern oceans.
Each genome was sequenced 30 times, producing tiny pieces about 150 base pairs long. Co-corresponding author Juliana Vianna, from the Pontifical Catholic University of Chile, painstakingly aligned each piece along a reference genome of the emperor penguin as a scaffold.
Comparisons told the team that penguins arose between 21 million and 22 million years ago, narrowing down the 10-to-40-million-year window determined previously from fossil penguins.
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