In a forthcoming study, geneticists from Yale University identify 17 hybrid tortoises with various combinations of Pinta genes on the nearby island of Isabela.
The existence of these Pinta-like tortoises came to light by chance when an initial sample of 27 tortoises from Isabela’s northernmost volcano Wolf turned up a youthful male with some unusual genes. This animal – officially dubbed PBR03 –appeared to be a first generation hybrid between a full-blown Pinta male and an Isabela female. "Lonesome George is not alone among Galapagos tortoises", the geneticists reported in Current Biology back in 2007.
Since then, they have worked hard to expand on this initial finding. Within a couple of years, they were able to return to Isabela, the Galapagos National Park mounting a huge expedition to extract blood from as many of Wolf Volcano’s tortoises as possible. The geneticists came away with samples from more than 1660 tortoises.
Earlier this year, the Yale team demonstrated that some of these tortoises had signs of Floreana ancestry, another species thought to have disappeared in the mid-19th century. In Table S1, buried in the supplemental information for the paper, they reported a cluster of seven tortoises with a strong affinity to the Pinta species.
The forthcoming paper, due to be published in Biological Conservation, extends this number to 17 individuals. Four of these look like they are first generation hybrids (F1), with one or other of their parents being of full Pinta stock. The rest seem to be second-generation (F2) hybrids. Several of the Pinta-like tortoises appear to be siblings, which seems reasonable for a species that lays clutches of up to 20 eggs at a time.
Given that the sampling may only have captured around 1/5th of the tortoises roaming on Wolf Voclano’s inhospitable flanks, the geneticists extrapolate to estimate there could be some 60 to 70 Chelonoidis abingdoni hybrids yet to be discovered. As five of the 17 tortoises are juveniles less than 20-years-old, it is also possible that there is still a purebred Pinta tortoise out there and breeding. If there are, however, the geneticists have not yet stumbled upon them.
The hybrids they have come across are only known from their blood. The actual animals still roam free. But there is a plan afoot to go and get them. “Our goal is to go back this spring to look for surviving individuals of this species and to collect hybrids,” says Adalgisa “Gisella” Caccone, senior author on the study, in a Yale University press release. “We hope that with a selective breeding program, we can reintroduce this tortoise species to its native home.”
Interestingly, the 17 hybrids are not randomly distributed but are most concentrated on the southwestern flanks of the volcano. The proximity of this location to Bank’s Cove – a popular watering hole for whalers and sealers – leads the authors to speculate that humans were responsible for the introduction of Pinta tortoises to Isabela some time during the last few centuries.
As incredible as this sounds, the alternative - that the tortoises got there by natural means - is less likely still. Although the islands are just 37 miles apart, any tortoise entering the sea from Pinta would be carried away from Isabela on prevailing northwesterly currents. Even if, by some freak means, a tortoise had floated southwest from Pinta to Isabela, its descendants would be located on the northern and not southwestern side of the volcano.
This important map should help the Galapagos National Park and Yale University geneticists as they attempt to relocate these hybrids for the purposes of captive breeding. I'd have liked to have seen George nonplus these relatives. That would have been entirely in keeping with his character. With his death on 24 June this year, this is a reunion that sadly can not take place.