Climate variability led to penguin evolution

Penguins live in some of the most extreme areas on Earth and have perfectly adapted to their environment. But how did they develop? The researchers have now gotten to the bottom of this question with the help of genome data from both living and extinct penguin species. The results show that climate variability in the past had a significant impact on the species evolution of marine winged predators. In addition, the researchers identified several genes that played an important role in certain adaptations.

Penguins originated more than 60 million years ago. Long before the polar ice sheets formed, they lost their ability to fly and instead used their wings to propel themselves while diving. With so many unique disciplines, different species can survive in some of the harshest environments on earth. But how did penguins evolve? This question has only been partially answered so far.

Adapt to the extreme

A team led by Theresa Kohl of the University of Copenhagen in Denmark included genome data from all 27 living and recently extinct penguin species, as well as 47 fossil species for the first time. They linked this data to past geological events. “Our findings help improve our understanding of how penguins enter the marine environment and successfully colonize some of the harshest environments on Earth,” the researchers said.

Using geographic reconstructions, Cole and her team confirmed the previous hypothesis that penguins originally evolved in New Zealand. From there, researchers say, they spread to Antarctica and South America. Climatic changes played an important role here, especially the last ice age, which began about 115,000 years ago and ended about 11,700 years ago. For penguin species that were restricted to a local habitat, the Ice Age was associated with massive population losses, while those with a large scale and those migrating saw population gains.

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Isolation and reunion

“Almost all species show a genomic imprint of a period of physical isolation during the last Ice Age with increased climate variability and environmental uncertainties,” Cole and colleagues say. “With increased ice volume during the last Ice Age, penguin species were likely forced to move from higher latitudes to isolated mid-latitude sanctuaries. As the climate warmed from the late Pleistocene to the Holocene, these species migrated again towards the poles, and recolonized the land masses and islands where they became habitable again.”

Species that evolved separately over thousands of years of isolation also came into contact with each other again. For researchers, the discovery solves an age-old mystery related to penguin evolution: genetic data point to an early separation and later exchange between certain species. Because interbreeding between closely related species is still observed to this day, Cole and her team postulate that the species diversified in spatial isolation, but later, after the Earth warmed again, produced common offspring again and thus exchanged genes.

Weak due to low rate of development

In their analyses, the researchers also identified several genes that appear to be important in allowing penguins to adapt to their specific environmental niche. “These included genes associated with sea diving, thermoregulation, oxygenation, underwater vision, taste, and immunity,” the authors said. Although penguins show some of the most profound evolutionary adaptations, Cole and her team found that they had one of the lowest evolutionary rates of any bird. “Several key features associated with their aquatic life were acquired by penguins very early in their diversification, and rates of change have slowed sharply to date,” the researchers explained.

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This may become a problem, particularly in light of the rapid progress in man-made climate change. “The current rate of warming, combined with limited refuges in the Southern Ocean, is likely to exceed the penguins’ ability to adapt,” the study authors said. “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. But as their evolutionary history shows, they are now a sort of early herald of the frailty of cold-adapted animals in an increasingly cold world. warming up quickly.”

Source: Theresa Kohl (University of Copenhagen, Denmark), Nature Communications, doi: 10.1038/s41467-022-31508-9

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