Contrasting population genetic structures in Amphipholis squamata, a complex of brooding, self-reproducing sister species sharing life history traits

Life history traits are among the major forces influencing the spatial organisation of biodiversity. Brooding species, lacking a planktonic larval phase, have a weak potential for dispersal and are prone to displaying strong spatial genetic structures of their populations. Self-reproduction allows a single individual to establish a new population. Using nuclear markers to assign specimens to species (1004 specimens) and sequences of the 16S mitochondrial gene (for a subset of 479 specimens) to estimate genetic differentiation, we analyzed spatial and bathymetric sampling of 14 locations along the French Mediterranean coast in order to investigate the genetic effects of brooding and self-reproduction on the Amphipholis squamata species complex. The spatial organisation of the complex appeared chaotic, illustrating the random nature of dispersal in these brooding organisms. Bayesian dating confirmed the old age of the species complex (approximately 10 million yr). The different species displayed contrasted levels of genetic diversity and differentiation, despite their similar and extreme self-reproduction rates. This study illustrates the role of stochastic dispersal on species assemblages and genetic structure, and suggests a strong influence of past demographic history on population genetic structure of co-distributed species.