Analysis of ancient DNA extracted from Antarctic sediment has shed new light on 6,000 years of the lives of Adelie penguins living on the Ross Sea coast, revealing the truth of how animals in the region responded to climate and environmental change over history.

Conducted by an international team of biology historians and investigators, the study has delved into earth’s ancient history through the metagenomic sequencing of 156 sediment samples recovered from colonies of Adelie penguins, to offer new insights into the species and the animals it has historically interacted with.

Through this analysis, researchers have been able to travel through time to detect the presence of other local species, including a range of birds, seals, and invertebrates; painting a picture of how species interaction changed over millennia. Findings from the study now reshape our understanding of life within the region over a span of thousands of years.

“We discovered, for example, that although the Antarctic silverfish is the dominant fish species consumed by Adelie penguins today, they have not always been the penguins’s most common prey,” said Dr Jamie Wood, a terrestrial ecologist and ancient DNA specialist from the University of Adelaide’s School of Biological Sciences and Environment Institute. 

“The bald notothen, a cryopelagic fish, was an important prey species 4,000 years ago. Populations appear to have declined in the southern Ross Sea, likely due to changing sea ice conditions, which led to a change in Adelie penguins’ diet.”

In one of the more surprising turn of events for researchers, the analysis of the sedimentary ancient DNA (sedaDNA) also revealed the presence of southern elephant seals, a species that no longer breeds on the Antarctic mainland but did – according to history’s natural records – some 1,000 years ago. 

“It was a complete surprise to find a potential former breeding colony of southern elephant seals at Cape Hallett on the Ross Sea coast,” said Dr Chengran Zhou of BGI Research, Wuhan, a joint lead author of the study.

“Although these seals no longer breed on the Antarctic mainland, we now have evidence to indicate they once did more than 1,000 years ago. There was no previous evidence of southern elephant seal occupation from Cape Hallett until we found their DNA in sediments. Cape Hallett is now the northernmost possible former breeding site identified from the Ross Sea region.”

Insights like those provided by this study will be an important part of developing approaches to conservation for animal populations in rapidly changing environments.

“Looking at biological records that span thousands of years gives us important insights into how species respond to environmental and climatic conditions that may not have been experienced in recent times,” said Dr Cole. 

“Understanding the resilience of species to these natural environmental and climatic perturbations gives us a better ability to predict how they might respond to future challenges.”

Future studies of Antarctic sedaDNA could well look even deeper into the past. 

“We found that even the oldest DNA fragments recovered from the sediments, from 6,000 years ago, were very well preserved, indicating there is potential for DNA that is hundreds of thousands of years old to be present in local deposits,” said Professor Guojie Zhang, senior author of the study, from the Centre for Evolutionary and Organismal Biology at Zhejiang University. 

Scientists are now excited for what technological developments in sedaDNA could mean for research in the future, particularly in the field of historical ecosystem analysis.

“The field of ancient sedimentary DNA research has largely been founded in the high-latitude permafrost soils and sediments of the northern hemisphere, where excellent records of past biodiversity have been recovered over the past two decades,” said Dr Wood.

“In contrast, terrestrial sediments from high latitudes of the southern hemisphere have received little attention. We believe our study is the first to report the recovery of ancient DNA from terrestrial sediments in Antarctica.”

The study – Sedimentary DNA insights into Holocene Adelie penguin population and ecology in the Ross Sea, Antarctica – was published earlier this month in Nature Communications.

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