FunNature & AnimalThey confirm that the fantastic giant tortoise is not...

They confirm that the fantastic giant tortoise is not extinct

In 2019 a live female tortoise was discovered on Fernandina Island , in the Galapagos. The specimen resembled Fernandina’s giant tortoise ( Chelonoidis phantasticus ), also known as the fantastic giant tortoise and of which only a single specimen was known, which was collected in 1906. The discovery of the second possible specimen gave geneticist Stephen Gaughran the opportunity to determine if both turtles are of the same species and therefore Chelonoidis phantasticus is not extinct.

Gaughran sequenced the genomes of both the live specimen and the one in the museum and compared them with those of 13 other species of Galapagos giant tortoises. The result is that the two known Fernandina tortoises belong to the same species, genetically different from all the others. It is confirmed, therefore, that the species has not become extinct.

The tortoise discovered in 2019 was named Fernanda because it came from Fernandina Island. At the time of the find, many ecologists doubted that it was a native phantasticus tortoise because it did not have the conspicuous enlargement of the carapace typical of the historical male specimen. It was also speculated that stunted growth might have distorted its characteristic features.

To definitively determine Fernanda’s species, Gaughran sequenced her complete genome and compared it to the one he was able to recover from the specimen collected in 1906. He also compared those two genomes with samples from the other 13 Galapagos tortoise species: three individuals from each of all 12 living species and one individual of the extinct C. abingdonii .

“We saw – honestly, to my surprise – that Fernanda was very similar to the one they found on that island over 100 years ago , and they were both very different from all the tortoises on the other islands,” Gaughran said.

Adalgisa Caccone has also participated in the identification process of Fernanda. “The finding of a live specimen gives hope and also opens up new questions, as many mysteries still remain,” he said. “Are there more tortoises in Fernandina that could be brought back into captivity to start a breeding program? How did the Fernandina tortoises colonize and what is their evolutionary relationship to the other Galapagos giant tortoises? This also shows the importance of using museum collections to understand the past.”

Gaughran is working on a tool that will allow the DNA of ancient specimens in the museum to be analyzed so that they can be compared with living specimens. “The software doesn’t care if it’s a seal or a tortoise, a human or a Neanderthal,” he said. “Genetics is genetics, for the most part. It’s in the performance that it matters what kind of creature the DNA comes from.”

The mystery of the fantastic turtle

Since the beginning of the 20th century, and based on little but convincing evidence, it has been suggested that giant tortoises could continue to inhabit the island of Fernandina.

The only known specimen of C. phantasticus or giant fantastic tortoise was found by the explorer Rollo Beck during an expedition in 1906. The fantastic part comes from the extraordinary shape of the male’s shell, which has an extreme enlargement along along the outer edge and looks like a saddle. The shell of Galapagos tortoises is like a saddle, but C. phantasticus is especially marked.

Since its discovery in 1906, the survival of the tortoise has been an unresolved issue for biologists . In 1964, 18 tracks attributable to tortoises were reported on the western slopes of the island. In the early 2000s, the presence of droppings and a possible observation from an airplane were reported. In 2014, possible turtle droppings were found again.

Fernandina Island has remained largely unexplored , due to extensive lava fields that block access to the interior. It is the highest of the Galapagos Islands and is geologically young.

Scientists estimate that Fernanda is over 50 years old , but she is small, possibly because the scarce vegetation in the area slowed her growth. There are hopes of finding more specimens, since in recent expeditions around the island, tracks and droppings of at least 2 or 3 other turtles have been detected.

 

Referencia: Jensen, E.L., Gaughran, S.J., Fusco, N.A. et al. 2022. The Galapagos giant tortoise Chelonoidis phantasticus is not extinct. Communications Biology. DOI: https://doi.org/10.1038/s42003-022-03483-w

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