South America has more canine species than anywhere else on Earth, and a surprising new UCLA-led genomic analysis shows that all of these canine animals evolved from a single species that entered the continent just 3.5 million to 4 million years ago. . Scientists have long believed that these diverse species evolved from multiple ancestors.
Even more surprising? The longest and shortest species are most closely related.
Some of the major genetic mutations that have led to the meteoric rise of extreme variations in the height, size and diet of South American canids have been artificially introduced over the past few thousand years through selective breeding to produce the staggering diversity on display. in a more well-known canine: the domestic dog.
The research, published in Proceedings of the National Academy of Sciencesshows how quickly new carnivore species can evolve and proliferate in non-competitive environments and provides conservation guidelines for endangered and threatened South American canids.
Ten species within the dog and wolf family, known as canids, live in South America today. Seven are foxes and three are more unusual: the short-eared dog, the forest dog, and the maned wolf.
For years, scientists had a theory about how South America had become home to so many species of canids. The continent had very few placental mammals and no ancestral canids, until the volcanic strip of land known as the Isthmus of Panama rose above sea level some 3 million years ago, allowing the free movement of animals between continents. That’s a short period of time for so many species to evolve from a single ancestor, so scientists assumed that multiple canid species had entered the isthmus at different times, creating extant and now extinct species.
To learn how these species were related and how long ago and by what genetic mechanisms they diverged, UCLA doctoral student Daniel Chavez, now a postdoctoral researcher at Arizona State University, and UCLA professor of evolutionary biology Robert Wayne sequenced 31 genomes that 10 Existing South American Canine Species. They traced the evolutionary relationships between the species by studying the locations, amount and types of genetic mutations between them.
Surprisingly, the genetic data pointed to a single ancestral population of canids that arrived between 3.5 million and 3.9 million years ago — before the isthmus had fully risen — and included about 11,600 individuals. The researchers said those ancestors must have made their way south through the newly developed Panama Corridor, then just a narrow strip of savanna generally not navigable to large populations.
“We found that all extant canids came from a single invasion that entered South America east of the Andes,” Chavez said. “By 1 million years ago there were already many species of canids, but they weren’t very genetically different because of gene flow, which happens when populations can easily interbreed.”
These species soon spread throughout South America, including the thin strip of land west of the Andes, adapting to different environments and becoming more genetically distinct. Today’s 10 species, the researchers found, all originated between 1 million and 3 million years ago.
They also found that the maned wolf, the largest and most leggy dog in South America and the only one to eat mostly fruit, and the shortest, the forest dog, which relies even more on meat than wolves and African wild dogs, are the most closely related. . Changes in the gene that controls leg length are responsible for the height difference.
“There were also many other now-extinct species of hypercarnivores associated with the forest dog,” Chavez said. “Maybe they were bigger in size, so to compete, the forest dog ancestors got smaller, while the maned wolf got bigger and eventually stopped vying for meat.”
Such rapid and extreme speciation by natural selection resembles the enormous differentiation among domestic dogs that occurred rapidly through artificial selection by humans.
“South American canids are the domesticated dog of the wild animal kingdom because they vary enormously in leg length and diet, and these changes happened very quickly, on the order of 1 to 2 million years,” Wayne said. “It’s a natural parallel to what we’ve been doing with dogs. This all happened because South America was free of these types of carnivores. There was a lot of prey and no large or medium-sized carnivores to compete with. In this empty niche, nature allowed such rapid radiation.”
The findings have also illuminated relationships between the species and identified genes that could help save species threatened by habitat loss and climate change.
“The Darwin’s fox, which currently survives on only one island off the coast of Chile and very small regions on the mainland, is a prime example of the need for conservation,” Wayne said. “We have proven large differences in variation between species at the genome level, with the most endangered species having very low levels of variation and genes that can be harmful. We can save small populations through thoughtful captive breeding programs.”
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Daniel E. Chavez et al, Comparative genomics reveals the evolutionary history, demographics and molecular adaptations of South American canids, Proceedings of the National Academy of Sciences (2022). DOI: 10.1073/pnas.2205986119
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