Abstract
Monitoring temporal changes in population genetic diversity and effective population size can provide vital information on future viability. The dusky gopher frog, Lithobates sevosus, is a critically endangered species found only in coastal Mississippi, with low genetic variability as a consequence of isolation and population size reduction. Conservation management practices have been implemented, but their efficacy has not been addressed. We genotyped individuals collected 1997–2014 to determine temporal trends in population genetic variation, structure, and effective size. Observed and expected heterozygosity and allelic richness revealed temporally stable, but low, levels of genetic variation. Positive levels of inbreeding were found in each year. There was weak genetic structure among years, which can be attributed to increased effects of genetic drift and inbreeding in small populations. L. sevosus exhibited an increase in effective population size, and currently has an estimated effective size of 33.0–58.6 individuals, which is approximately half the census size. This large ratio could possibly be explained by genetic compensation. We found that management practices have been effective at maintaining and improving effective size and genetic diversity, but that additional strategies need to be implemented to enhance viability of the species.
Highlights
The maintenance of genetic variation within populations and species is a primary concern in conservation biology because this variation allows species and populations to adapt to their changing environments (Frankham et al 2004)
When analyzing the data year-by-year the amount of genetic variation within L. sevosus remained relatively stable throughout the sample period, with the exception of year 2013
Genetic compensation suggests that when population sizes are low, most individuals participate in breeding activities. This compensation would lessen genetic variation reduction in times with low population numbers by reducing inbreeding. These results suggest that L. sevosus might be experiencing genetic compensation in concert with effective conservation management practices that have stabilized Ne/Nc ratios and genetic variation over the sample period
Summary
The maintenance of genetic variation within populations and species is a primary concern in conservation biology because this variation allows species and populations to adapt to their changing environments (Frankham et al 2004). Without this adaptive potential, populations are at an increased risk of endangerment and extinction. Small, isolated populations have lower amounts of genetic variation and are more prone to inbreeding depression (Frankham 1996; Richter and Nunziata 2014). Species residing in wetland habitats, especially amphibians, are vulnerable because in addition to relying on both wetland and upland habitats, most of the natural wetlands crucial to amphibian breeding events have been destroyed or degraded, causing a reduction in habitat and wetland species’ population sizes (Dahl 2000; Beebee 2005; Curado et al 2011)
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