Galapagos Tortoise Bottleneck with Surprising Results

Recovery of a nearly extinct Galapagos tortoise despite minimal genetic variation
This article discusses a study of a dramatic bottleneck after a reduction of a species of Galapagos tortoise to 12 remaining females and 3 males.  They were then bred in captivity for over 30 years and produced over 1,700 offspring, which were then reintroduced to the island in the early 1990s.  The species successfully continued to reproduce, indicated by the growth in the percentage of juveniles hatched on the island (0% in 1994, 3% in 2004, and 24% in 2007).  Furthermore, there was a high level of size distribution of the tortoises, the population was surprisingly heterogeneous. This result was interesting because the original population brought into captivity was very small (an estimated population size less than 8) and theoretically, very low levels of genetic diversity should correlate with low levels of long-term persistence and adaptation.  The study concluded that some endangered species seem capable of successful and rapid recovery despite a low level of genetic variation.  They do note, however, that these results can't be confidently extrapolated to any long-term conclusions because, despite the 40 year length of this study, the long life span of tortoises mean that there have not been many generations yet.