Detection of Genetic Patterns in Endangered Marine Species Is Affected by Small Sample Sizes

SIMPLE SUMMARY: Knowledge of genetic diversity is crucial to improve conservation plans for endangered species and ensure their long-term persistence. However, it may be difficult to accurately estimate genetic diversity when it is unfeasible to obtain sufficiently large sample sizes, which is often the case for marine endangered species. Here, we use Patella ferruginea as a model to investigate how small sample sizes affect genetic diversity estimates. We show that small sample sizes do not always hamper the detection of genetic patterns in endangered marine species, even though caution is needed when genetic divergence among populations is weak. ABSTRACT: Knowledge of Genetic diversity and its spatial distribution is crucial to improve conservation plans for endangered species. Genetic tools help ensure species’ long-term persistence by unraveling connectivity patterns and evolutionary trajectories of populations. Here, microsatellite genotypes of individuals from populations of Patella ferruginea are used to assess the effect of sample size on metrics of within-and between-population genetic diversity by combining empirical and simulated data. Within-population metrics are slightly to moderately affected by small sample size, albeit the magnitude of the bias is proportional to the effective population size and gene flow. The power of detecting genetic differentiation among populations increases with sample size, albeit the gain of increasing the number of sampled individuals tends to be negligible between 30 and 50. Our results line up with those of previous studies and highlight that small sample sizes are not always a hindrance to investigating genetic patterns in endangered marine species. Caution is needed in interpreting genetic patterns based on small sample sizes when the observed genetic differentiation is weak. This study also highlights the importance of carrying out genetic monitoring in seemingly well-preserved but potentially isolated populations.