Researchers at Yale University have discovered a lonely giant tortoise whose Species Were Last Seen Over 100 Years Ago

Researchers at Yale University have discovered a lonely giant tortoise whose Species Were Last Seen  ...

Fernanda, the only known living Fernandina giant tortoise (Chelonoidis phantasticus), has now been moved to the Galápagos National Park's Giant Tortoise Breeding Center on Santa Cruz Island. Credit: Courtesy of the Galápagos Conservancy

Evolutionary scientists were surprised when they discovered a single, tiny female tortoise in 2019 that lives on one of the Galapagos Islands' most isolated islands. Only one other tortoise, a massive male found in 1906, has ever been discovered on Fernandina Island, a remote island on the famous archipelago's western tip.

Fernanda, the 50-year-old tortoise, and the male specimen from the 20th century, both were identified in a Yale University study that is now housed at the California Academy of Sciences. This increase increases the number of known members of Chelonoidis phantasticus.

Despite the findings, there are still many questions unanswered.

"Vast amounts of genomes are similar between the two animals, but the mechanism that explains how this happened we just don't know," said Adalgisa Caccone, a senior research scientist and lecturer in Yale's Department of Ecology & Evolutionary Biology and senior author of the study. "This also underscores the importance of using museum collections to investigate the past."

Fernanda, named after her Fernandina Island home, is the first of her species to be identified in over a century. Stephen Gaughran, a Princeton geneticist, analyzed DNA from a specimen taken from the same island more than a century ago and discovered that Fernanda and the museum specimen are members of the same species and genetically distinct from all other Galápagos tortoises.

According to the Galapagos Conservancy, there are thought to be 15 distinct species of giant tortoises on the Galapagos Islands.

The new discovery demonstrates that the two Galapagos tortoises discovered on Fernandina Island belong to their own lineage and are more closely related to each other than to any other species of Galapagos tortoises, whose numbers have decreased by 85 to 90% since the early nineteenth century, largely due to the arrival of whalers and pirates who slaughtered them for food.

"The discovery of one alive specimen gives hope but also raises fresh questions as many mysteries remain," said Caccone, a member of Yale's Faculty of Arts and Sciences. "Is there any evidence that tortoises colonized Fernandina might be brought back to captivity to begin a breeding program?"

Volcanic eruptions on Fernandina Island have pushed tortoises to their deaths, including around 25 in the previous two centuries. Scientists have speculated that lava flows altered vegetation.

The giant tortoise from Fernandina Island (Chelonoidis phantasticus) was only known from this single specimen, discovered in 1906, before "Fernanda" was discovered in 2019. Credit: California Academy of Sciences

Conservationists may begin a captive breeding program if more tortoises are discovered on the island of Fernandina.

Deciphering the evolutionary relationship between the two Fernandina tortoises might be harder. For one, they both appear quite different. The male specimen has a large, protruding carapace characteristic of saddleback tortoises, while Fernanda has a smaller, smoother shell. This shape variation could be due to slowed growth as a result of limited food options.

Researchers discovered differences in the mitochondria, the energy-producing portion of cells that are passed down from the mother. Fernanda is a hybrid, the progeny of a Chelonoidis phantasticus male and a C. nigra female from the island of Floreana, the larger neighbor of Fernandina.

Diverse tortoise species, such as C. nigra, have been known between the Galapagos islands, including Isabela island, where many hybrids between the endemic species C. becki and the extinct C. nigra have been discovered. It is possible that a C. nigra female similarly found its way to Fernandina and mated with a male from C. phantasticus, leaving its mitochondrial DNA to all of her descendants.

Caccone believes that the male specimen now in the California museum is likely a true representation of the original species. However, more tortoises from Fernandina must be found to solve this new puzzle, according to Caccone.

In the following years, evolutionary biologists will study these and other topics.

"These tortoises are the largest cold-blooded terrestrial herbivore on Earth, and they play a significant ecological role," Caccone said. "They are so important not only because of their iconic status, but also because they are an essential component of ecosystem stability in the Galapagos.

"There is still a lot we don't know, and what we learn will provide guidance to help protect them and with them the fragile and unique place on Earth they call home."

Evelyn L. Jensen, Stephen J. Gaughran, Nikos Poulakakis, Washington Tapia, Christian Sevilla, Jeffreys Málaga, Carol Mariani, James P. Gibbs, and Adalgisa Caccone, 9 June 2022, Communications Biology. DOI: 10.1038/s42003-022-03483-w

The Galápagos National Park Directorate, the Galápagos Conservancy, Re:Wild, Island Conservation, the Ecuadorian Ministry of the Environment, the California Academy of Sciences, and the Yale Center for Research Computing were all involved in this research.

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