It has been fun reading the blogs from various Wolf Expedition participants. I remained in the mountains of California while they wandered the slopes of the volcano; but with all the stories and photos, I almost feel like I was there. I certainly was in spirit. As coordinator of the Giant Tortoise Restoration Initiative (GTRI), I would now like to lay out where this exciting project is headed.
Thirty-two saddleback tortoises are now being held in corrals at the Fausto Llerena Tortoise Center on Santa Cruz — waiting for genetic analyses. Amongst the several thousand native Wolf tortoises and many hybrid tortoises on Wolf Volcano, another 148 saddleback tortoises there now have a brand new microchip under the skin of their back leg. Blood samples from all 180 tortoises (32 in captivity and 148 on the slopes of Wolf) are ready to be shipped north to Yale University (awaiting the appropriate paper work), where Gisella Caccone and her team will begin the process of determining just what tortoise species are represented in their DNA.
As 2016 marches on, the tortoises’ DNA will begin to reveal the secrets of 200 years of tortoise reproduction on Wolf Volcano. Within the next six months, we should have a general idea of the ancestry of each tortoise. Then with a more refined methodology, we will find out how much of each tortoise’s genome is from one of the extinct species, as well as how much overall genetic diversity has been captured within the identified Pinta or Floreana genomes. Based on these results, the geneticists will recommend exactly which of the 32 tortoises should be used to initiate the breeding program — including which males should be matched with which females — to ultimately capture the highest possible level of Pinta or Floreana genomes and the highest genetic diversity in the offspring produced. Over time, this will involve a lot of tortoise matchmaking, guided by computer simulation.
The Galapagos National Park Directorate (GNPD) working with the scientists of the GTRI from Galapagos Conservancy, Yale, SUNY, etc., will then initiate a highly targeted breeding program, with the long-term goal of restoring the Pinta and Floreana tortoise populations. The program may begin with only a few pairs for each population; it all depends upon the results of the genetic analyses. These tortoises will be held under the same general conditions as the fifteen Española tortoises, which have been successfully reproducing in captivity for over fifty years to slowly repopulate that island. Our Tortoise Center review in November 2014 resulted in improvements to the programs and facilities; we, along with the GNDP, are dedicated to ensuring that all captive tortoises remain fit and healthy.
You might ask: What about those tortoises with lower percentages or lower diversity of the target species? Rather than incorporate them into the breeding program, they will likely be released directly onto either Floreana or Pinta Islands. If any of the 32 tortoises show other ancestries (there is quite a mix of tortoises on Wolf Volcano, from more of the islands than just Pinta and Floreana), we will make tortoise-specific recommendations to the GNPD on whether to return them to Wolf Volcano or release them on some other island.
If analysis of the samples from the 148 tortoises left on Wolf Volcano identify high value tortoises (with a high percentage of Pinta or Floreana genome and high diversity within that), we will work with the GNPD to carry out additional trips to Wolf to collect those animals, and potentially collect new unmarked animals with a similar saddleback shell shape. If these tortoises are even better choices for the breeding program, adult tortoises already in the program might then be released onto Pinta or Floreana. Every time we change the breeding pairs to improve the level of the targeted genomes, we also increase the overall genetic diversity, moving at a tortoise pace toward a better outcome.
But the work doesn’t stop there. As the tortoises begin to reproduce, we will want genetic analyses of the offspring. The majority of these young will be released onto their target island. However, if some have unusually high percentages of the target genome, they might remain in captivity to eventually be incorporated into the breeding program.
This work is long-term and involves constant decision-making as the genetics of more and more tortoises are evaluated and that information is incorporated into the system. That’s part of what makes it so exciting.
You might ask: Why not just release all of the tortoises collected from Wolf directly onto Pinta or Floreana — let nature take its course? We consider captive breeding combined with direct releases to be the optimal approach. Captive breeding will allow us to recapture as much of the original genes of the Pinta and Floreana tortoises as possible — to enhance their restoration on their home island.
The decision to establish a captive breeding program and rear the young to 4-5 years before releasing them into the wild is directly related to survival of the young. In captivity, nearly all tortoises that hatch survive. By rearing them to 4-5 years old before releasing them, they have more than a 50% chance of surviving to adulthood. But in the wild, in most years, the majority of the hatchlings that emerge from the nests die due to predation, desiccation, and other factors. This is natural for a very long-lived animal. Imagine if 10,000 female tortoises across the Archipelago laid 20 successfully hatched eggs per year and they all survived — the Islands would quickly become overpopulated with tortoises. Then imagine how many eggs could be laid annually by the historical 100,000 or more female tortoises.
But when you are rebuilding a population from scratch, it’s better to ensure survival of more of the young. And which young do we want to eventually dominate the population? Those with the highest levels of Pinta and Floreana genes.
Eventually the breeding program will end and all of the remaining captive tortoises will be released into the wilds of Pinta and Floreana. That decision, perhaps 10-20 or more years away, will be based on the health and size of the tortoise population on each island, the status of the genetic diversity of those populations, and various other factors.
Are you totally confused now? Don’t worry — we’ll keep it all straight. While we are sometimes mired in the minutiae of the work, we keep the long-term vision in mind: Pinta and Floreana Islands with hundreds, if not thousands, of saddleback tortoises wandering among the cactus, sleeping, feeding, mating, nesting, dispersing seeds, and living out their centuries-long lives; island ecosystems restored to closer to their pristine, pre-human condition with a myriad of species that depend, at least in part, on the tortoises.
I dream of a day when the Galapagos Archipelago abounds with more than 100,000 tortoises, with continually increasing populations, until one day they equal tortoise numbers from before humans stepped foot in that wonderful world: a Galapagos always and forever with its full complement of iconic giants.
Dr. Linda Cayot is GC’s Science Advisor and has played an important role in Galapagos conservation efforts for more than 30 years.
Photo credits: Wolf Volcano tortoises © Paul M. Gibbons; Pinta Island © Linda Cayot; Floreana Island © Patty Jaramillo.