Penguins – 60 million years of evolution reconstructed
If you think of penguins, you probably automatically see the iconic birds in the icy environment of Antarctica. The association “penguins = Antarctica” is deeply rooted in our minds, even though some species also feel at home in temperate latitudes and in the tropics. A new study now turns this “law of nature” upside down. A large international team of 40 researchers has reconstructed more than 60 million years of evolutionary history and found that penguins evolved long before the polar ice caps formed.
There have been several phylogenetic studies of penguins, but these only examined the genomes of species that still exist today or, if fossil penguins were included, only a portion of their genetic information. The new study, however, published in the journal Nature Communications, was the first to analyze the genomes of all living and recently extinct penguin species (27 in total) and compare them with data from fossil penguins (47 species). Only by doing so was the research team able to reconstruct the evolution of penguins. Modern lineages go back only a few million years, leaving most of the penguin evolution that began 60 million years ago in the dark.
“More than three-quarters of all penguin species are extinct now,” Dr. Daniel Ksepka, a paleontologist at the Bruce Museum in Greenwich, Connecticut, and co-author of the study, told The New York Times. “You have to look at the fossil record, or you’re only getting a fragment of the story.”
Fossils of long-extinct penguins have been found along the equator, and many of them predate the glaciation of the Antarctic continent. “They lived through some of the hottest times in Earth’s history, when it was five degrees warmer at the equator,” Ksepka said. “They basically evolved in an ice-free context.”
The study found that the evolution of penguins, which originated in Australia and New Zealand, was driven by changes in climate and ocean currents. In the penguins’ genetic material, the research team encountered signatures that suggest there was an alternation between small populations surviving in climatic refugia during times when conditions were unfavorable everywhere else, and population growth and recolonization during times when conditions were better. As temperatures dropped, penguins were pushed farther north, and when temperatures rose again, they migrated toward the pole and colonized newly available habitats.
In addition, the researchers identified a number of genes that may be responsible for the penguins’ adaptations as they moved from the tropics to Antarctica. These include abilities such as building up blubber for thermoregulation, tolerating low oxygen levels during deep dives, underwater vision, and factors that control body size.
Compared to other birds, evolution in penguins was very slow, the research team also reported in their study. They assume that penguins developed the most important features needed for life in and under water very early and quickly, and that further adaptations were added only in small steps until today. This means that their body plan was already pretty perfect from the very beginning.
“Although when most people think of penguins, they picture them among ice floes and being chased by leopard seals, penguins evolved to be aquatic creatures before the polar ice sheets formed! Over time, they evolved characteristics that allowed them to colonise a wide range of marine environments from the tropics to Antarctica. This paper provides a step change in our understanding of which genes underpin these different adaptations,” says Professor Richard Phillips, seabird ecologist at the British Antarctic Survey and co-author of the study.
In conclusion, the scientists say in their study that their research on understanding the effects of past climate events on population sizes is critical to understanding how their populations might respond to future climate changes.
Julia Hager, PolarJournal
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