Captive breeding and the fitness of reintroduced species: a test of the responses to predators in a threatened amphibian

1. Although captive breeding and reintroduction is a high-profile management tool for many threatened species, it is unclear how long-term captive breeding can influence fitness attributes such as natural defences to predators. 2. Induced defences that have evolved in the Mallorcan midwife toad Alytes muletensis in response to introduced predators were compared in natural and reintroduced populations that had a common ancestry, and in short-term and long-term captive populations that differed in ancestry. 3. Defences against predators were maintained in a reintroduced population derived from stock that had passed through three to eight generations of captive breeding prior to release into a predator-free area. Heterozygosity did not differ between natural and reintroduced populations, but the reintroduced population displayed lower allelic richness. 4. A comparison between populations maintained for different lengths of time in captivity revealed a significant reduction in one defensive trait in stock maintained for more than eight generations. Neutral genetic variation (i.e. heterozygosity and allelic richness) did not differ between the short-term captive population and a natural population, but there was a significant loss of genetic variation in the long-term captive population. 5. Synthesis and applications. The results suggest that relatively high levels of heterozygosity and important fitness attributes can be maintained for a few generations in breeding programmes for threatened species despite small numbers of founders and the absence of natural selection. Nevertheless, both fitness and heterozygosity may eventually start to deteriorate in the long term, and this may have implications for reintroduction strategies.