Host-mediated dispersal shapes spatial distribution of genetic variability in marine symbionts

Assessing the importance of intrinsic and extrinsic factors that shape the spatial distribution of genetic diversity of symbionts has been a topic of debate for decades. While host-mediated dispersal is an important driver of gene flow in many terrestrial metazoan symbionts, few studies have identified the drivers of symbiont genetic differentiation in the marine realm, where habitats are comparatively more homogeneous and long-distance dispersal is common. In the present study, we perform a meta-analysis of existing studies examining symbiont spatial genetic diversity to determine which symbiont- and host-related traits shape the patterns of genetic differentiation of metazoan symbionts, while also considering technical aspects of each study. Specifically, we wanted to assess the influence of biological traits and/or technical aspects in (1) detecting genetic differentiation in marine symbionts, and (2) shaping the minimum spatial scale at which genetic differentiation was detected. By assessing genetic diversity of mtDNA markers, we found that the spatial scale at which studies are conducted was a crucial predictor of both detection of genetic structure and scale at which differentiation of marine symbionts was detected. Symbiont-based traits did not influence genetic structure, however, host-mediated dispersal was the only biological trait that shaped genetic structure of marine symbionts by influencing the spatial distribution at which differentiation was detected.