Importance of Genetic–Fitness Correlations for the Conservation of Amphibians

SIMPLE SUMMARY: Threatened animal species live in small and isolated populations, often with a reduced number of individuals and reduced genetic diversity. In this review, we summarise studies on amphibian species that examined the effect of genetic diversity on the fitness of individuals or populations. We found evidence for the positive association between genetic diversity and different estimates of fitness where low genetic diversity is associated with lower fitness. Published studies are however scarce, concentrated on a handful species and with a high proportion of non-significant results reported. For the maintenance of amphibian and other animal populations, it is important to increase the research effort in this topic and, for imperilled populations, enhance genetic diversity through different types of conservation measures. ABSTRACT: Endangered animals suffer from isolation of their habitats. Isolation leads to a reduction in population size as well as a decrease in genetic diversity and a concomitant increase in the risk of extinction. Amphibians are the most endangered vertebrate class. Besides habitat loss, fragmentation and isolation, amphibians are threatened by emerging diseases e.g., chytrid fungus or Ranavirus. By employing experiments, researchers investigate whether changes in genetic diversity within or among isolated populations affect amphibian fitness. While genetic diversity estimates are based on molecular markers, typically microsatellites, fitness is mostly measured as tadpole performance in rearing experiments often under varying environmental conditions. Tadpole performances (e.g., body mass, growth rate and survival) have been found to be negatively affected by low genetic diversity, as several studies have found a positive association between genetic diversity and these fitness traits. Moreover, infection with pathogens also seems to be more likely in individuals or populations with lower genetic diversity. Overall, these genetic–fitness correlations seem to be more pronounced or detectable in smaller, declining populations but not in larger populations. Genomic studies, which sample a larger fraction of the genome, are still scarce in the conservation genetic literature on amphibians. These are likely to increase in upcoming years and may reveal adaptive variants that protect against dangerous pathogens or environmental changes. Altogether, genetic–fitness correlation studies should be a priority in order to develop effective management plans for the genetic rescue of isolated, imperilled amphibian populations.