Microsatellite genotypes for temporal monitoring of the Floreana Island Galapagos Giant Tortoise captive breeding program

Captive breeding programs benefit from genetic analyses that identify
relatedness between individuals, assign parentage to offspring, and track
levels of genetic diversity. Monitoring these parameters across breeding
cycles is critical to the success of a captive breeding program as it
allows conservation managers to iteratively evaluate and adjust program
structure. However, in practice, genetic tracking of breeding outcomes is
rarely conducted. Here, we examined the first three offspring cohorts
(2017 – 2020) of the genetically-informed captive breeding program for the
Floreana Island Galapagos giant tortoise, Chelonoidis niger. This captive
breeding program is unique as the Floreana tortoise has been extinct since
the 1800s, but its genome persists, in part, in the form of living hybrids
with the extant Volcano Wolf tortoise, Chelonoidis becki. Breeding over
the study period took place at the Galapagos National Park Directorate
breeding facility in four corrals, each containing three females and two
males. Using 17 microsatellite markers, we were able to assign parentage
to 94 of the 98 offspring produced over the study period. We observe that
despite the addition of more founders since the pilot breeding program,
the effective population size remains low, and changes to the arrangements
of breeding corrals may be necessary to encourage more equal reproductive
output from the males. This study demonstrates the value of hybrids for
species restoration and the importance of continually reassessing the
outcomes of captive breeding.