Survival to metamorphosis is positively related to genetic variability in a critically endangered amphibian species

Isolated small populations typically have reduced genetic variation and are more susceptible to local extinction. Examining the relationship between genetic variability and survival is important for conservation because it provides insight on evolutionary potential and population viability. We studied genetic associations of survival from egg to metamorphosis in the largest population of critically endangered dusky gopher frogs Lithobates sevosus. This approach allowed us to examine whether heterozygosity-fitness correlations (HFCs) existed in an r-selected species with large effect size, whereas previous research on HFCs has largely focused on k-selected species often with low effect sizes. Our objectives were to determine if genetic-fitness associations exist, if associations are a result of inbreeding and if natural selection against inbreeding has occurred. Specifically, we examined averaged population responses and HFC in relation to (1) mortality within egg clutches and (2) differential survival of offspring through metamorphosis. To do so, we used eight microsatellite DNA markers to compare genotypes across three life-history stages from a single year in the following temporal order: adults, eggs and metamorphs. We discovered a strong genetic association with survival in early life stages. In terms of average population responses, we documented a within-cohort decrease in FIS with life-history stage progression (adults: FIS=0.067; eggs: FIS=0.063; metamorphs: FIS=-0.134), high FST between eggs and metamorphs (FST=0.113), and a locus that had larger than expected FST. We found positive genetic-fitness associations for survival of egg clutches and for survival to metamorphosis. We believe that inbreeding is the primary cause; however, we also found evidence suggesting existence of purging selection against a deleterious mutant linked to a microsatellite locus. Survival of individuals with greater genetic variability should prolong persistence of this isolated population. Our study underscores the importance of species management focused on preservation of genetic diversity.