Testing spatial models of genetic connectivity for European Raja clavata and Sepia officinalis in response to seascape resistance

Predicting influences of habitat distribution and heterogeneity on species gene flow is now widely acknowledged as a key step in optimising effective marine management practices. Commonly applied models of geographic influence such as isolation by distance (IBD) and isolation by oceanic distances (IBO), though often effective at predicting the genetic connectivity of pelagic species, fail to incorporate potential influences of habitat by single corridor or multiple corridors on the genetic and movement connectivity for non-pelagic and demersal-obligate species, as found on continental shelf systems. Least-cost path (LCP) and isolation by resistance (IBR); a novel approach based on Circuit Theory principles of random walk, counters these limitations by integrating the effects of single and multiple pathways on connectivity by distances taken between locations over habitat shapes of assigned resistances optimised a priori. Applications of these models have been largely restricted to terrestrial systems despite the potential for improving predictions of connectivity for marine habitat specialists. Using available genetic, distribution and habitat data from two co-distributed and predominately demersal species Sepia officinalis and Raja clavata, we were able to identify that IBO explained the connectivity of R. clavata while S. officinalis connectivity was influenced by IBR and the LCP by habitat configuration. With this study we provide a simple framework for developing tests of genetic connectivity that indicate some of the processes underpinning patterns of genetic structure.