Deriving connectivity from relatedness: broad-scale isolation-by-distance in the shanny Lipophrys pholis L.-L. Jeannot, C. Mouronvalle, C. Peyran, C. Olabarria, M. Beger, A. Blanco, S. Planes Abstract: Knowledge about dispersal patterns of marine organisms is vital for understanding population dynamics and designing appropriately scaled protected areas and fisheries management. Assessing the extent to which populations are connected by larval exchange has been traditionally approached from delineating genetically differentiated populations. Inferring these patterns for species with high gene flow remains a challenge as they often show panmixia over large spatial scales. In these cases, genetic connectivity may be revealed through the combination of population-based and kinship-based approaches. Here, we assess population structure and relatedness of the shanny Lipophrys pholis over 500 km along the Western Iberian Peninsula coastline using 27 microsatellites developed for the purpose of this study. As expected, based on given its long larval duration stage, we found a high level of gene flow throughout the study area. However, a weak but significant pattern of isolation-by-distance was detected by Mantel tests as well as large-scale relatedness patterns, indicating decreasing a decrease in genetic similarity with distance at the scale of the Western Iberian Peninsula. Conversely, we provided evidence of fine-scale connectivity at the smaller scale of the Atlantic Islands of Galicia National Park (Spain). These findings highlight the potential to reveal previously undetected genetic differentiation within a well-connected population through a combination of population-based and kinship-based approaches. Our results may be broadened to other coastal organisms featuring similar life-history traits, including a relatively long larval phase, as well as comparable environmental conditions favoring dispersal by ocean currents, which could be directly applied for the management and conservation of Northeast Atlantic marine species. Full Changelog: https://github.com/lljeannot/Lpholis_relatedness/commits/v1.0

This work is framed within the project ORGANISE in which A. B. was supported by the Axencia Galega de Innovación (GAIN), Xunta de Galicia (grant ED481B 2018/68).