Local adaptation with gene flow in a highly dispersive shark

Area of Science:

• Marine Biology
• Population Genetics
• Conservation Genomics

Background:

• Adaptive divergence is expected in species across heterogeneous environments.
• Gene-environment association studies are limited in elasmobranchs.
• The bronze whaler shark (Carcharhinus brachyurus) is widely distributed and exploited in southern Africa.

Purpose of the Study:

• To assess genomic diversity in C. brachyurus across a heterogeneous southern African environment.
• To identify neutral and adaptive genetic variation.
• To understand population structure and gene flow in relation to environmental factors.

Main Methods:

• Genome-wide single nucleotide polymorphisms (SNPs) were generated using 3RAD.
• Differentiation-based genome scans (outflank) and genotype-environment analyses (redundancy analysis, latent factor mixed models) were employed.
• Analysis of neutral and putatively adaptive SNPs was conducted.

Main Results:

• Moderate and even genomic diversity was found across neutral SNPs, with high gene flow and no significant population structuring.
• A total of 234 differentiation-based outlier and candidate SNPs associated with bioclimatic variables were identified.
• Putatively adaptive SNPs revealed two clusters and deep divergence between Angola and Namibia/South Africa.

Conclusions:

• Evidence for adaptive divergence in response to a heterogeneous seascape was found in C. brachyurus, despite high gene flow.
• This study highlights adaptive potential in a large, mobile shark species.
• Findings are expected to inform conservation and management strategies for C. brachyurus populations.