LIFE SCIENCE

Why did the clumsy abandon the sky and choose the ocean?


The ancestors of land vertebrates landed on land from the ocean, and the ancestors of birds flew from land to the blue sky, while penguins, as birds, abandoned the blue sky about 60 million years ago, once again adapted to the marine ecosystem, became the strongest divers among birds, and successfully survived in the extreme environment on Earth.

On July 19, a Joint Team of Chinese and Foreign Scientists led by Chinese scientists reconstructed the origin and evolution process of penguins through multidisciplinary joint methods, and used this as a case to reveal the impact of environmental changes, climate and geological events on penguin speciation, and found a series of molecular basis for key traits to explain how penguins can adapt to the marine ecological environment for the second time. The results of the research were published in Nature Communications.

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The emperor penguin living on the Antarctic continent is courtesy of Shenzhen Huada Life Science Research Institute

Multidisciplinary joint puzzle solving

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Modern penguins painted by Teresa Cole and others

For quite some time in the past, the evolutionary history of the penguin family is confusing. Scientists were puzzled by the relationship between the six branches of penguins and have never been able to fully clarify the relationship between penguin species. The known penguin fossils have 32 genera, which increases the difficulty of straightening out the evolutionary relationship between penguins.

Without understanding the evolutionary relationship within the penguin, it is impossible to understand how the penguin gradually evolved into the present form and characteristics, nor can it accurately understand how the penguin evolved under the shape of the polar environment, nor can it answer the question of why the ancestors of the penguins’ birds re-adapted to the ocean.

In this study, for the first time, scientists collected data on the morphology and geography of almost all 74 known penguin species, including fossil species, on a global scale, and constructed a high-quality genomic dataset of all 24 extant penguin species and 3 modern extinct penguin species.

“This is the first time that the high-quality genomes of all modern penguin species, including subspecies, endemic clades, and recently extinct penguin species, have been made available globally.” The first author and co-corresponding author of the paper, Theresa Cole, a postdoctoral fellow at the Danish Biodiversity Genome Research Center, introduced, “This study also integrates genomics and paleontology, integrates the comparative analysis of extinct species and living taxa, clarifies the evolutionary relationship between penguin members, and also provides many new methods for evolutionary genome research.” ”

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Reconstructed penguin evolutionary relationships Teresa Cole and Zhou Chengran

Reconstruct the evolution of the penguin family

About 65 million years ago, shortly after the Cretaceous mass extinction event, the ancestors of penguins appeared in the Paleo-Zealand region. At that time, The ancient Zealand was isolated from the mainland, and the distribution of the continents in the southern hemisphere was close to where it is today, and only the Antarctic continent was still connected to the South American continent by land bridges. It was from the Ancient Zealand region that the ancient penguins began to spread near the ancient land bridge.

40 million years ago, the land bridge connecting the two continents of Antarctica and South America was broken, and the remnants of the land bridge became today’s Antarctic Peninsula. Since then, Antarctica has been completely surrounded by the ocean, and as the strait gradually opens, the ocean currents surrounding the Antarctic begin to form, and the climate of the Antarctic continent becomes colder.

34 million years ago, the Antarctic ice sheet formed. For a long period of history, penguins were mainly distributed in and around the southern coast of Old Zealand, antarctic peninsula and South America. There were many giant penguin species during this period, such as the ancient crowned penguin of Carbide, which is about 2 meters tall, which is the largest penguin known so far.

Until about 14 million years ago, the common ancestor of modern penguins appeared in ancient South America. They spread to Antarctica and first differentiated on the Antarctic Peninsula and the Antarctic continent to form the genus King Penguin, and then other modern penguin branches have emerged.

“The common ancestor of living penguins appeared about 14 million years ago, after which changes in climate and environment have driven rapid differentiation of penguin species, accompanied by complex gene flows, which have had a huge impact on the shaping of the morphological diversity of living penguins.” Zhang Guojie, the corresponding author of the paper and a professor at the Center for life evolution research at Zhejiang University, told China Science Daily.

About 2.6 million years ago, the Earth’s climate changed drastically, and with the advent of the Quaternary ice age, the penguin family also underwent rapid evolutionary events, and most of the living species were differentiated in a relatively short period of time. Their range has expanded considerably, covering the southern coasts of Antarctica and other major continents in the southern hemisphere, basically laying the foundation for today’s species pattern and becoming the most dominant seabird in the Southern Ocean. In the process, the gradually increasing Antarctic polar current is likely to provide an important boost to the spread of penguins.

“Over the past 60 million years, penguins have undergone tremendous environmental changes, especially from warm subtropics to ‘ice hell’, but after each environmental upheaval, penguin branches have been able to stand out and thrive. This suggests that penguins are extremely adaptable to evolution, and makes us optimistic about the future of these magical animals. Zhang Dexing, a researcher at the Institute of Zoology of the Chinese Academy of Sciences, said in an interview.

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The historical distribution of penguins and the speculative spread, the arrows are the possible dispersal paths of penguins, and the colored areas are the distribution range of penguins. Zhou Chengran painted

How environmental carvers shape penguins

When the research team looked at the penguins on the scale of evolution, they found that their body size was gradually becoming smaller; Morphological features such as beak and limbs are gradually transformed into features more suitable for the marine environment; The number of penguin species also showed the opposite trend of temperature due to the influence of ice age events.

“Tropical or temperate organisms have traditionally been thought to have a faster rate of evolution than polar organisms.” Dr. Chengran Zhou, co-first author of the paper and a member of the Shenzhen Huada Institute of Life Sciences, mentioned, “But we found that high-latitude penguins such as emperor penguins have a faster evolution rate than low-latitude penguins. This means that the pressure caused by the Antarctic environment and historical climate fluctuations have promoted the spread and differentiation of penguins, and to a certain extent, the adaptation of high-latitude species to the polar environment. ”

In addition, the research team also found a series of key genes, summarizing the “genetic secrets” of penguins adapting to cold environments and underwater life.

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Penguin functional gene display Zhou Chengran and Fang Miaoquan are all painted, and the photo is from pixabay

For example, underwater vision ability. Compared with air, the light transmittance of seawater is much worse, and due to the absorption of seawater, light is rapidly weakened, and only a small amount of short-wavelength light such as blue light can reach a depth of about 200m underwater. “Underwater vision has always been a huge challenge for potential birds, and in penguins, some light-sensitive genes have mutations, affecting light conduction pathways, promoting the recognition of blue light and ultraviolet light, and giving penguins keen vision in underwater and low light environments.” Fang Miaoquan, a bioinformatics analyst at The University of Life Sciences in Shenzhen, explained that it is precisely by virtue of the way of multi-visual genetic changes that penguins have obtained better underwater vision.

For another example, as birds with the strongest diving ability, hemoglobin and myoglobin in penguins have significant differences from the conservative sites of other birds, and the king penguin genus also has a difference from the conservative sites of other penguins. “These features allow penguins to use oxygen in their blood more efficiently, making itself a ‘highly efficient oxygen-enriched chamber’, extending the dive time.” Fang Miaoquan added. (Source: China Science Daily, Hu Minqi, Teng Wenyu)

Related paper information:https://doi.org/10.1038/s41467-022-31508-9



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