Limited dispersal explains the spatial distribution of siblings in a reef fish population

Extensive larval dispersal and a high degree of planktonic cohort mixing were long presumed to disrupt kin aggregations in marine environments. Yet, recent genetic studies of diverse marine taxa have suggested that kin may be found in close proximity to each other after settlement, raising interesting questions about the ecological and behavioral processes that could generate these patterns. We drew on sibship reconstruction to test whether kin cohesion and/or the scale of dispersal could explain patterns of relatedness in the coral reef fish Elacatinus iori. We genotyped 4074 recently settled individuals along a 41 km transect on the Belize Barrier Reef. Because most individuals in the population were unrelated, we found that high-confidence sibling assignments required a large number of microsatellites (>= 55). Using 71 microsatellites, we documented 371 sibling pairs which were non-randomly distributed on the reef: 50% were <= 3 km apart and 99% were <= 18 km apart. The spatial distribution of sibling pairs was congruent with predictions from the limited dispersal hypothesis, and we found no evidence that siblings disperse cohesively. These results underscore the importance of (1) accounting for the relative abundance of different relationship types within a population to accurately identify siblings and (2) carefully applying spatial analyses to discriminate between alternative ecological kin structuring mechanisms. More broadly, this study provides a framework for linking spatial distributions of siblings to the processes that generate them, highlighting the potential for sibship data to provide new insights into marine larval dispersal.