The importance of long-term genetic monitoring of reintroduced populations: inbreeding in the natterjack toad (Epidalea calamita)

Genetic monitoring is an important, but frequently lacking, component of management actions to support long-term persistence in reintroduced populations. Populations that remain small, due to demographic processes and genetic diversity, are more likely to experience a second extinction event. The natterjack toad (Epidelea calamita) is legally protected in Britain and was the subject of a reintroduction programme in the 1990s. However, subsequent genetic assessment has been mostly lacking. The aim of this study was to assess the genetic diversity of two reintroduced populations of natterjack toads in order to inform conservation management. Adults were sampled and nine microsatellites amplified to assess neutral genetic variation within each site and for comparison with the source population. Inbreeding was observed at the reintroduction sites, as evidenced by high FIS values (0.43 and 0.72), low observed compared to expected heterozygosities, and significant deviation from Hardy-Weinberg equilibrium. Observed heterozygosity is currently lower in the reintroduction sites than it was in the source population at the time of the reintroductions (Red Rocks: 0.15±0.20; Talacre: 0.12±0.20; Ainsdale (source): 0.29). Evidence for a bottleneck was not found, although this is likely a result of sampling overlapping generations. No withinsite population structuring was observed. Such low genetic diversity has not previously been recorded in any natterjack population. Genetic rescue, combined with pool creation, is the most viable option for safeguarding the species at these sites into the future. Our work highlights the importance of ongoing genetic monitoring, in collaboration with conservation organisations, to support conservation management.