It’s the question that drives scientific discovery. It’s also the question most often asked of Dr. Stephen Divers and the medical team that assisted him with endoscopically sterilizing or sexing 59 tortoises on a trip to the Galápagos Islands earlier this year.
At the invitation of Dr. Joe Flanagan, senior veterinarian at the Houston (Texas) Zoo, Drs. Stephen Divers, UGA Professor of zoological medicine, and Sam Rivera, senior director of animal health at Zoo Atlanta, traveled to the Galápagos to perform laparoscopic sterilizations of young adult tortoises of hybrid genetics. They also performed endoscopic sexing of genetically pure juvenile tortoises raised in a captive breeding program for release in the wild. The work was done as an assist to the Galápagos Conservancy and Galápagos National Park in reestablishing native species of tortoises to the various islands that make up the archipelago.
Dr. Kelsey Trumpp, second-year resident in the CVM, and Nia Chau, a zoological medicine nurse at the Veterinary Teaching Hospital, traveled with Divers, Flanagan, and Rivera to assist and learn from the surgeries.
The Galápagos as Lab
When the research vessel Beagle landed on the Galápagos in 1835 with Charles Darwin aboard, the islands were a living laboratory for studying some 2,000 unique species with pure genetic stock. Darwin made his name observing those animals for genetic changes or adaptations that occur in any given species over time.
Darwin’s observations of wildlife on the island inspired him to postulate on the origin of species, developing the theory of evolution and the notion of survival of the fittest. At that time, the isolation of the islands prevented the interbreeding of species unique to each. The insulation from outside influences was so absolute that the origins of tortoises native to the various islands that make up the whole of the Galápagos could be identified by the shapes of their shells.
But the lack of diversity ultimately delivered dilution. People drawn by whale hunting in the islands not only introduced competing species, but they also became predators, shuffling individual animals from island to island or removing them altogether to keep as pets, to populate zoos, or even for food.
In the 16th century Galápagos tortoises numbered more than 250,000. Today, there are approximately 35,000.
Divers, a faculty member on the Zoological Medicine Service at the UGA Veterinary Teaching Hospital, said the individuals sterilized earlier this year originated in the Galápagos but hatched in captivity to animals whose island of origin was unknown at the time. Once their ancestry could be determined using genetic tools, they were found to be of hybrid origin, with no island to call their permanent home. To be released in the wild, they would have to be sterilized to keep from contaminating the gene pool of tortoises on islands where they might be released.
“If you could release them back into the wild, they would have so much more space. Their welfare would be so much better,” Divers said. “If we could sterilize them, we could send them out even if they were hybrids (of mixed island genetics) knowing that they can’t reproduce so they live a happy life and don’t interfere with the pure genetic stock of that island.”
The Giant Tortoise Restoration Initiative began a project of captive rearing in 1965 to restore endangered species in the islands. By 2017, the program returned more than 7,000 juvenile tortoises to their islands of origin – including Española, Isabela, Pinzón, San Cristóbal, Santa Cruz, and Santiago. In May 2010, 39 hybrid adult tortoises Divers, Rivera and Flanagan sterilized in 2009 were released onto Pinta Island to help with vegetation management following the eradication of non-native goats. They paved the way for later release of a breeding population of tortoises by controlling vegetation previously managed by the goats.
The tortoises Divers and his team operated on were, to put it plainly, mutts. But they were carefully screened prior to sterilization to ensure that they were not made of stock valuable to efforts to replenish imperiled tortoise species.
“There is some disagreement as to whether animals from different islands are subspecies of the same species or if they’re genuinely different species,” said Trumpp, who will do her third year of residency at Zoo Atlanta. “While the different species or subspecies from different islands can interbreed and produce offspring there’s some evidence to suggest they may overall be less fertile and might be less robust and might not do as well and that’s why they don’t want those animals reproducing.”