Seascape genetics at its finest: dispersal patchiness within a well-connected population

Abstract

ABSTRACTDispersal is a main determining factor of population structure and variation. In the marine habitat, well-connected populations with large numbers of reproducing individuals are common but even so population structure can exist on a small-scale. Variation in dispersal between populations or over time is often associated to both environmental and genetic variation. Nonetheless, detecting structure and dispersal variation on a fine-scale within marine populations still remains a challenge. Here we propose and use a novel approach of combining a clustering model, early-life history trait information from fish otoliths, spatial coordinates and genetic markers to detect very fine-scale dispersal patterns. We collected 1573 individuals (946 adults and 627 juveniles) of the black-faced blenny across a small-scale (2km) coastline as well as at a larger-scale area (<50kms). A total of 178 single nucleotide polymorphism markers were used to evaluate relatedness patterns within this well-connected population. Local retention and/or dispersal varied across the 2km coastline with higher frequency of SHORT-range disperser adults; representing local recruitment; towards the southwest of the area. An inverse pattern was found for juveniles, showing an increase of SHORT-range dispersers towards the northeast. This reveals a complex but not full genetic mixing and suggests oceanic/coastal circulation as the main driver of this fine-scale chaotic genetic patchiness within this otherwise homogeneous population. When focusing on the patterns within one recruitment season, we found large differences in temperatures (from approx. 17oC to 25oC) as well as pelagic larval duration (PLD) for juveniles from the beginning of the season and the end of the season. We were able to detect fine-scale differences in HIGH-range juvenile dispersers, representing distant migrants, depending on whether they were born at the beginning of the season, hence, with a longer PLD, or at the end of the reproductive season. The ability to detect such fine-scale dispersal patchiness will aid in our understanding of the underlying mechanisms of population structuring and chaotic patchiness in a wide range of species even with high potential dispersal abilities.