Research used ancient DNA techniques to obtain the first genetic data on several extinct species, including the completely extinct Caribbean barbed rats and “giant huts”, to reconstruct the origins and evolutionary history of this enigmatic group.
The caviomorphs include live 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, almost all of these species have become extinct due to human activity – hunting, habitat loss, and introduction of invasive species to Caribbean islands. This study is the first to compare genetic data from this largely extinct group of rodents – using data from living Caribbean rodents known as hutias, along with data from five extinct Caribbean species ranging from mouse-sized to dog-sized animals – to determine their evolution history and biogeographical origin. Understanding the mechanisms behind the diversification of these animals in the Caribbean provides unique new insights into how species adapt and respond to new environments.
The Caribbean is an important system for studying 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 great for studying evolution for several reasons. They are often remote, which means that only a select few groups of organisms even reach islands. Mammals rarely colonize islands, but rodents have made it to the Caribbean, making this archipelago a perfect place to study colonization events and island development. Our ancient DNA analysis provided the first molecular data for several extinct Caribbean rodent species, so we could find out when and how they came to the Caribbean. ‘
Despite their wide range of ecological niches and different morphologies, all of these rodents evolved from a single surface colonization event around 18 million years ago. These results provide an important new example of adaptive radiation, in which a single mainland colonizing line evolves into novel shapes on a group of islands. This evolutionary event represents the largest increase in body size ever recorded in rodents, and possibly the largest for any line of mammals. The co-author Dr. Selina Brace of the Natural History Museum said: “It is amazing to believe that a single colonization has resulted in such extreme gigantism in rodents. These powerful rodents grew to be more than thirty times larger than their mainland relatives. ‘
Co-author Professor Ian Barnes of the Natural History Museum commented, “The Caribbean is a fascinating region to study, but its hot, humid environment breaks down DNA quickly, making it very difficult to get data from ancient bones. Combined with the very rapid changes in shape and size that animals often experience when colonizing islands, it is often difficult to reconstruct the evolutionary relationships of extinct species from the region. ‘
Most of the surviving rodent species in the Caribbean are critically endangered. Co-author Professor Samuel Turvey of the Zoological Society of London said: “The last survivors of Caribbean rodent radiation – the hutias of Cuba, Hispaniola, Jamaica and the Bahamas – are global priorities for protection. Their incredible evolutionary history means we cannot allow these neglected species to become extinct – we urgently need protective measures to protect the remains of this remarkable group of mammals. ‘
The paper was published in Molecular Biology and Evolution on Monday, October 12, 2020.
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