Age-structured genetic analysis reveals temporal and geographic variation within and between two cryptic rockfish species

Abstract

The spatial patterns of genetic structure among juveniles of long-lived species can reveal the extent of interannual and geographic variation in realized larval dispersal as well as the processes that determine ecologically relevant patterns of population connectivity. However, few studies examine this temporal and spatial variation over large portions of a species' geographic range or between cryptic species that overlap in their range. Despite the potential for long-dis- tance dispersal in blue rockfish Sebastes mystinus, a previous study of adults revealed two geo- graphically distinct, cryptic species. To determine year-to-year variation in the patterns of spatial connectivity and to elucidate the potential ecological mechanisms involved in shaping new year- classes and maintaining cryptic species, we sampled juveniles within California, USA, where both cryptic species coexist. Using microsatellite markers, we found geographic and temporal variation in the number of individuals from these distinct cryptic species within 2 new year-classes of juve- nile S. mystinus. We also found differences in the geographic patterns of genetic structure of the 2 cryptic species. Whereas one species exhibited little or no spatial genetic structure across the study region, the other exhibited a complex geographic pattern of genetic structure, with little or no genetic structure among regions, but small-scale structure within a region. The results of this study demonstrate that the spatial scales and patterns of realized dispersal of pelagic larvae vary geographically, interannually, and between closely related species with similar life-history strate- gies. Therefore, estimates of dispersal based on larval duration and patterns of adult structure need to be interpreted cautiously.