Interplay between isolation by distance and genetic clusters in the red coral Corallium rubrum: insights from simulated and empirical data

The analysis of genetic structure is an important tool for the management of harvested and threatened species. Individual clustering methods and tests of Isolation by Distance (IBD) are currently used in this context. They have been applied to the red coral Corallium rubrum but some questions remained due to contrasted results among studies and limits in their interpretations. In this study, we used simulated and empirical data for a better understanding of the genetic structure in this species. We tested the impact of IBD between demes, sampling scheme and of clustering methods (BAPS, STRUCTURE or DAPC) on the inferred structure. By matching simulated scenarios to the empirical data, we first confirm that the genetic structure of the red coral is characterized by a combination between IBD and weak genetic breaks. Then, we demonstrate how the sampling scheme influences the results of the clustering methods. We also reveal the contrasted efficiencies of these methods to recover real demes or groups of demes in a context of IBD. Overall, our study underline the interest of comparing the results of different clustering methods and of using simulated data for interpreting empirical genetical data.