Thanks to DNA testing from tortoise bones that were almost a century old and found in museums in Wisconsin, the United Kingdom and Galapagos, an international team writing in the journal PLOS One this week has identified a second species on the island.
They concluded that a few hundred giant tortoises living on the eastern side of Santa Cruz are distinct from a second, larger population living less than 6.2 miles away on the western side. The new species, C. donfaustoi, is named after a retiring park ranger who spent decades protecting the tortoises.
Adalgisa “Gisella” Caccone, a senior research scientist at Yale who was the lead author on the study, said her team was inspired to take a closer look at the turtles by retired USGS herpetologist Tom Fritts, who noted slight differences in the shells of the tortoises.
Caccone said the findings are helping scientists better understand just how these tortoises made it to Santa Cruz and the process that led to their diversity on the island.
“We were very surprised but also very intrigued,” she said. “The closest relative of C. donfaustoi lived on an island west of Santa Cruz named San Cristóbal. We figured the colonization of the tortoises on Santa Cruz happened twice - once they colonized the western flank and then the eastern flank.”
Caccone said the discovery of the new species also could go a long ways to conserving the tortoises, given that they face a range of threats - from farming that overlaps with their ranges as well as hotels and other tourism-related developments.
“From a conservation standpoint, recognition of this new species will help promote efforts to protect and restore it, given that its low abundance, small geographic range, and reduced genetic diversity make it vulnerable,” Caccone and the other authors wrote. “In particular, further investigation is needed to better determine C. donfaustoi‘s population size and structure, range, movement patterns, location of nesting zones, and habitat requirements, as well as ongoing threats and effective ways to mitigate them.”
While the larger western population on the island numbers about 2,000 and lives mostly in a protected national park, the smaller number of newly designated Eastern Santa Cruz tortoises – estimated at around 250 – are more vulnerable.
“Maintaining the two species’ biological isolation is critical,” the researchers wrote. “Of particular importance is ensuring that no human-mediated transport of tortoises occurs between the two sides of Santa Cruz Island given that the two species’ ranges are now linked via a single agricultural zone.”