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Rodents of unusual size: A new study using Ancient DNA reveals the origins of the remarkable Caribbean giant rodents

A new study by scientists from the Natural History Museum and the Zoological Society of London (ZSL) has found that the incredibly diverse Caribbean caviomorph rodents, which range in size from 0.1kg-200kg, evolved into radically different species across the islands of the western Caribbean following a single colonisation event

The research used ancient DNA techniques to obtain the first genetic data from several extinct species, including the completely extinct Caribbean spiny rats and “giant hutias”, to reconstruct the origins and evolutionary history of this enigmatic group.

Caviomorphs include living South American rodents such as guinea pigs, chinchillas and capybaras. There used to be over 30 species of Caribbean caviomorphs, the largest of which were the size of bears. However, nearly all of these species are now extinct due to human activities – hunting, habitat loss, and the introduction of invasive species to Caribbean islands. This study is the first to compare genetic data from across this largely extinct group of rodents – using data from living Caribbean rodents called hutias, together with data from five extinct Caribbean species ranging from mouse-sized to dog-sized animals – to resolve their evolutionary history and biogeographic origins. Understanding the mechanisms behind how these animals diversified across the Caribbean provides unique new insights into how species adapt and react to new environments.

The Caribbean represents an important system to study evolutionary patterns and processes. Dr Roseina Woods, who worked on this study as part of her PhD at the Natural History Museum, said: 'Islands are brilliant for studying evolution for several reasons. They are often remote, meaning that only a few select groups of organisms reach islands in the first place. Mammals rarely colonise islands, but rodents did make it to the Caribbean, so this archipelago is a perfect place to study colonisation events and island evolution. Our ancient DNA analyses produced the first molecular data for several extinct Caribbean rodent species, allowing us to uncover when and how they arrived in the Caribbean.'

Despite their wide range of ecological niches and diverse morphologies, all of these rodents evolved from a single overwater colonisation event around 18 million years ago. These findings provide an important new example of adaptive radiation, where a single colonising mainland lineage evolves into novel forms across a group of islands. This evolutionary event represents the greatest increase in body size ever recorded in rodents, and possibly the greatest for any mammal lineage. Co-author Dr Selina Brace from the Natural History Museum said: ‘It’s amazing to think that a single colonisation led to such extreme rodent gigantism. These mighty rodents became more than thirty times larger than their mainland relatives.’

Co-author Professor Ian Barnes from the Natural History Museum noted: 'The Caribbean is a fascinating region to study, but its hot, wet environment quickly degrades DNA, making it very difficult to obtain data from ancient bones. Combined with the very rapid changes in shape and size that animals often undergo when they colonise islands, it’s often difficult to reconstruct the evolutionary relationships of extinct species from the region.'

Most of the Caribbean’s surviving rodent species are highly threatened with extinction. Co-author Professor Samuel Turvey from the Zoological Society of London said: 'The last few survivors of the Caribbean rodent radiation – the hutias of Cuba, Hispaniola, Jamaica, and the Bahamas - are global priorities for conservation. Their incredible evolutionary history means that we cannot allow these neglected species to become extinct – we need urgent conservation action to protect what’s left of this remarkable group of mammals.’

 

ENDS

The paper was published in Molecular Biology and Evolution on Monday 12 October 2020.

Notes for editors

Media contact: Tel: +44 (0)779 969 0151 Email: press@nhm.ac.uk


About the Natural History Museum:

The Natural History Museum is both a world-leading science research centre and the most-visited natural history museum in Europe. With a vision of a future in which both people and the planet thrive, it is uniquely positioned to be a powerful champion for balancing humanity’s needs with those of the natural world.

It is custodian of one of the world’s most important scientific collections comprising over 80 million specimens. The scale of this collection enables researchers from all over the world to document how species have and continue to respond to environmental changes - which is vital in helping predict what might happen in the future and informing future policies and plans to help the planet.

The Museum’s 300 scientists continue to represent one of the largest groups in the world studying and enabling research into every aspect of the natural world. Their science is contributing critical data to help the global fight to save the future of the planet from the major threats of climate change and biodiversity loss through to finding solutions such as the sustainable extraction of natural resources.

The Museum uses its enormous global reach and influence to meet its mission to create advocates for the planet - to inform, inspire and empower everyone to make a difference for nature. We welcome over five million visitors each year; our digital output reaches hundreds of thousands of people in over 200 countries each month and our touring exhibitions have been seen by around 30 million people in the last 10 years.

About ZSL

ZSL (Zoological Society of London) is an international conservation charity working to create a world where wildlife thrives. From investigating the health threats facing animals to helping people and wildlife live alongside each other, ZSL is committed to bringing wildlife back from the brink of extinction. Our work is realised through our ground-breaking science, our field conservation around the world and engaging millions of people through our two zoos, ZSL London Zoo and ZSL Whipsnade Zoo. For more information, visit www.zsl.org

A lack of funding - as a result of the current pandemic - has put ZSL’s world-leading expertise in science and conservation in serious jeopardy. ZSL needs urgent support to keep its scientists investigating wildlife diseases such as Covid-19, and its conservationists working in the field to protect the wildlife and ecosystems on which we rely. Find out more at www.zsl.org/donate.