Abstract
Connectivity and local adaptation are two contrasting evolutionary forces highly influencing population structure. To evaluate the impact of early-life traits and environmental conditions on genetic structuring and adaptation, we studied two sympatric fish species in the Western Mediterranean Sea: Symphodus tinca and S. ocellatus. We followed an individual-based approach and measured early-life history traits from otolith readings, gathered information on environmental variables and obtained genome-wide markers from genotyping-by-sequencing (GBS). The two species presented contrasting population structure across the same geographic gradient, with high and significant population differentiation in S. ocellatus, mostly determined by oceanographic fronts, and low differentiation and no front effect in S. tinca. Despite their different levels of genetic differentiation, we identified in both species candidate regions for local adaptation by combining outlier analysis with environmental and phenotypic association analyses. Most candidate loci were associated to temperature and productivity in S. ocellatus and to temperature and turbulence in S. tinca suggesting that different drivers may determine genomic diversity and differentiation in each species. Globally, our study highlights that individual-based approach combining genomic, environmental and phenotypic information is key to identify signals of selection and the processes mediating them.
Highlights
Connectivity and local adaptation are two contrasting evolutionary forces highly influencing population structure
Information is used in genome-wide association studies (GWAS), which can identify signals of adaptation to both environmental conditions (EAAs) and phenotypic traits through phenotype association analysis (PAAs)
Significant differences among sampling locations were detected with PERMANOVA for all phenotypic and environmental variables with three exceptions: pelagic larval duration (PLD) growth rate and Hatching date in Symphodus ocellatus and PLD in S. tinca (Table S1)
Summary
Connectivity and local adaptation are two contrasting evolutionary forces highly influencing population structure. The two species presented contrasting population structure across the same geographic gradient, with high and significant population differentiation in S. ocellatus, mostly determined by oceanographic fronts, and low differentiation and no front effect in S. tinca Despite their different levels of genetic differentiation, we identified in both species candidate regions for local adaptation by combining outlier analysis with environmental and phenotypic association analyses. There is a lack of individual-based studies in natural marine populations, preventing an accurate knowledge of the relationships between genomic data, environment and early life phenotypes in determining population structure in environmental gradients This approach can be undertaken in species were individual based information during dispersal phases can be obtained, such as benthic fishes. The study of individually based genomic variation associated to early-life history traits across geographic gradients in sympatric fish can provide insights into the adaptive potential of species while considering both connectivity and selection
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