Penguins live in some of the most extreme regions on earth and have adapted perfectly to their environment. But how did they develop? Researchers have now got to the bottom of this question with the help of genome data from living and extinct penguin species. The results show that past climate variability had a significant impact on the species evolution of winged marine predators. In addition, the researchers identified several genes that played an important role in specific adaptations.
Penguins arose more than 60 million years ago. Long before the polar ice sheets formed, they had lost their ability to fly and instead used their wings to propel themselves while diving. With numerous unique specializations, the various species are capable of surviving in some of the most extreme environments on earth. But how did the penguins evolve? This question has only been partially answered so far.
Adaptation to the extreme
A team led by Theresa Cole from the University of Copenhagen in Denmark has now included genome data from all 27 living and recently extinct penguin species, as well as 47 fossil species, for the first time. They related this data to past geological events. “Our findings help improve our understanding of how penguins got into the marine environment and successfully colonized some of the most extreme environments on Earth,” the researchers said.
Using biogeographical reconstructions, Cole and her team confirmed the earlier hypothesis that penguins originally evolved in New Zealand. From there, the researchers say, they spread to Antarctica and South America. Climate changes played an important role here, especially the last ice age, which began around 115,000 years ago and ended around 11,700 years ago. For penguin species that were restricted to a localized habitat, the Ice Age was associated with severe population losses, while species with a wider range and those that migrate experienced population gains.
isolation and reunion
“Almost all species show the genomic signature of a period of physical isolation during the last ice age with increased climate variability and environmental uncertainties,” report Cole and her colleagues. “As ice volume increased during the last ice age, penguin species were likely forced from the high latitudes to isolated mid-latitude refugia. As the climate warmed from the late Pleistocene to the Holocene, these species migrated back toward the poles, recolonizing landmasses and islands as they became habitable again.”
Species that had evolved separately over thousands of years of isolation also came into contact with each other again. For the researchers, this finding solves a long-standing mystery of penguin evolution: the genetic data indicate both an early separation and a later exchange between certain species. Since matings between closely related species are still observed today, Cole and her team assume that the species diversified in spatial isolation, but later, after the earth had warmed again, produced common offspring again and thus exchanged genes.
Vulnerable due to low evolution rate
In their analyses, the researchers also identified several genes that appeared to be important in allowing the penguins to adapt to their specific ecological niche. “These included genes associated with diving in the sea, thermoregulation, oxygenation, underwater vision, taste and immunity,” the authors report. Although penguins exhibit some of the most profound evolutionary adaptations, Cole and her team found that they have one of the lowest evolutionary rates of any bird. “Many of the key traits 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 explain.
In view of the rapidly advancing man-made climate change, this could become a problem. “The current rate of warming, coupled with the limited refuges in the Southern Ocean, is likely to far exceed the penguins’ ability to adapt,” the authors said. “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. But as their evolutionary history shows, they are now a kind of early herald of the vulnerability of cold-adapted fauna in a rapidly warming world.”
Source: Theresa Cole (University of Copenhagen, Denmark), Nature Communications, doi: 10.1038/s41467-022-31508-9