The four-foot-tall Emperor penguin of Antarctica may be the most iconic member of this unique family of birds, but 17 other species of penguins populate the Southern Hemisphere, many of them confined to isolated islands that make them hard to study.
That's likely why an entirely new species of gentoo penguin has been overlooked on the Kerguelen Islands — or, as the French refer to them, the Desolation Islands — located nearly 2,000 miles from any permanently inhabited landmass. An international team of penguin experts led by Chilean and University of California, Berkeley biologists announced the discovery — the first new penguin species named in more than 100 years — in a paper published last month in the journal Communications Biology.
The scientists provided genetic evidence that what was once thought to be one widely dispersed species is actually four separate species of gentoo penguin. One of these was previously unrecognized because, except for slight differences in size and vocalization, it looks like every other gentoo: a white underside and black back, which are optimal for escaping predation while enabling prey capture in an ocean environment. Yet it is clearly genetically different — what scientists refer to as a cryptic species.
The researchers also concluded that three previously recognized subspecies of gentoo penguins are genetically distinct and should be elevated to full-fledged species status.
The fate of the newly recognized species — the southeastern gentoo penguin, Pygoscelis kerguelensis — and two others are uncertain as global warming affects the Antarctic and sub-Antarctic regions they occupy. Only the southern gentoo, now called Pygoscelis ellsworthi and the only species to reside in Antarctica, is predicted to be minimally affected or possibly even advantaged because of an expanded distributional range.
"In Antarctica, of course, other species, not the gentoo, are threatened by climate change," said Juliana Vianna , one of the paper's senior authors and a professor of ecosystems and environment at Andrés Bello National University in Santiago, Chile. "But the gentoo is of most concern in the sub-Antarctic region," an area of widely separated islands north of Antarctica governed by numerous countries, including Chile, South Africa, France, the Netherlands, Australia and New Zealand,
"It's very important that conservation institutions in all the different countries involved recognize and take appropriate action to save these three gentoo penguin species," she added.
Biologists reach a consensus
Vianna and co-senior authors Rauri Bowie , a professor of integrative biology at UC Berkeley, and Elie Poulin, a professor at the University of Chile in Santiago, corralled penguin experts from around the world to collaborate on a new genomic analysis of gentoo penguin populations. Several of the authors had previously described subspecies of the gentoo — as many as six — though not all of them were in agreement. The paper represents a consensus, based on new whole genome sequences of 64 individuals from 10 breeding colonies, for the first time spanning nearly the entire geographical range of the gentoo penguin. The study also includes comparisons of physical characteristics, ranging from coloration and vocalizations to the timing of breeding, diet and feeding behaviors.
"There's probably no species of penguin where the taxonomy has been more debated than the gentoo penguin," said Bowie, a curator in UC Berkeley's Museum of Vertebrate Zoology. "For over 100 years it's been controversial as to how many species or how many subspecies there are. What this paper does is try to address that question using cutting-edge integrative approaches."
Bowie and Vianna have worked together for nearly 10 years to understand the origins and diversity of penguins. In 2019, they published a landmark paper showing that penguins first arose around Australia and New Zealand about 22 million years ago, with Emperor and King penguins splitting off and occupying Antarctica and the sub-Antarctic, respectively. About 12 million years ago, with the rise of the circumpolar current, other penguins were carried throughout the sub-Antarctic, occupying many small islands and archipelagoes and spreading as far north as the African and South American continents.
Gentoos differ from most other penguin species in having a generalized diet, eating essentially anything they can chase down in the water. Today, with plunging krill populations, this generalized strategy is a survival advantage. Penguins that eat more specific food items, like Emperors and Adélies, are declining in numbers, while the gentoos that coexist with them on the Antarctic peninsula are increasing in population size.
The gentoos' generalized diet indirectly led to the evolution of the new species, the researchers argue. Because the birds are content to eat what's in front of them — including fish, krill, squid and cuttlefish — they don't travel far from their breeding colony and nest in the same place year after year. As a result, the populations on isolated islands developed behavioral and ecological adaptations to their specific region that over time have been reinforced through selection across the genome. This led to speciation during the past 300,000 to 500,000 years, aided by the isolation of these remote islands and by the Antarctic Polar Front, a temperature and salinity barrier in the Southern Ocean that also is a barrier to animal movement.
North of the Polar Front, where the water is warmer and saltier, there's now the eastern lineage — Pygoscelis taeniata — on the Crozet, Marion and Macquarie Islands, and the northern lineage — Pygoscelis papua — which is restricted to the Falkland/Malvinas and Martillo Islands in South America.
Right on the Polar Front lies the newly described, though low-population, southeastern lineage — Pygoscelis kerguelensis — which evolved on Kerguelen Island and likely nearby Heard Island. Below the Polar Front is found the southern and most populous lineage — Pygoscelis ellsworthi — which thrives on the Antarctic Peninsula, coastal Antarctica and South Georgia Island.
Genomes reveal genetic adaptations
The genomic analysis, which was led by the paper's lead author, University of Chile graduate student Daly Noll, incorporated a more representative sample of genes across the entire genome than previous studies. It also involved thousands of genetic variations called single nucleotide polymorphisms (SNPs). The analysis showed how these species evolved to adapt to their environments. For example, the southern gentoo that is thriving in Antarctica shows genetic changes associated with adaptation to extreme polar environments, with a larger number of genes related to heat generation, fat and lipid storage and light perception. The latter likely reflects adaptations to seasonal daylight variation and ice reflectivity.
In contrast, the eastern gentoo has an increased number of genes linked to energy-efficient carbohydrate metabolism and enhanced diving capacity. These genes, which are associated with oxygen transport and use, blood vessel formation, mitochondrial activity and lung development, likely support prolonged underwater activity in low-productivity oceans.
The northern gentoo of South America, however, showed gene enrichment for digestion-related processes and pathways involved in cardiac contraction and muscle excitation. The researchers suggest that these patterns reflect metabolic and physiological adaptations that support sustained foraging activity in the water.
To assess how the gentoo penguins will adapt to climate change, the researchers used climate prediction models to see where the animals' preferred habitat will be in 2050. Under a moderate climate change scenario, all of the island-inhabiting sub-Antarctic species will find their current islands uninhabitable, with few or no nearby suitable islands to which they can move. The Antarctic species, however, is likely to expand deeper into the continent as other Antarctic species — Emperor, Adélie and chinstrap penguins — decline because of the disappearance of sea ice and the krill that grow under the ice.
Vianna noted that many other non-Antarctic penguins are expected to suffer from habitat loss because of climate change and the increasing impacts of warming oceans, habitat destruction, predation by rats and dogs, competition from commercial fisheries and entrapment in nets.
"In terms of climate change, island species that have really low population sizes could be compared with the sub-Antarctic gentoo penguins," she said. "Galapagos and other island penguin species, because they're endemic to these islands, will find no place to go after a change in their environment. Those islands are very isolated, and these penguins cannot adapt easily to colonize any other region."
The amount and variety of data acquired for the study is unprecedented and will have other uses, Bowie said. Vianna is already searching through penguin genomes to find the genetic changes associated with survival from avian influenza, which is now ravaging penguin, bird and mammal populations worldwide. Such studies could help identify populations most at risk from the disease.
"Whole genome sequencing has transformed our ability to not only look at adaptation from a perspective of how things diversify, but it has really important conservation value," Bowie said.
Co-authors with Bowie and Vianna include biologists from Australia, Spain, Venezuela, South Africa, the United Kingdom, France, Argentina, Monaco and Brazil. Daly Noll of the University of Chile in Santiago is first author of the paper.
