Evidence for divergent selection and spatial differentiation in a
putative zona pellucida gene is indicative of local adaptation in
Pacific cod
Abstract
Genetic differentiation has been observed in marine species even when no
obvious barriers to gene flow exist. The study of highly differentiated
outlier loci can provide information on how genetic variation might
contribute to local adaptation. A locus which aligned to a predicted
zona pellucida sperm-binding protein 3 gene (ZP3) in Atlantic cod was
previously identified in Pacific cod populations as a high
differentiation outlier. In other marine species, ZP3 is involved in
reproductive isolation, local adaptation, and has neofunctionalized as
an antifreeze gene, but the function of this genomic region is not
understood in Pacific cod. We sequenced a 544 bp region of ZP3 in 230
Pacific cod collected from throughout their geographic range. Here we
show that ZP3 haplotypes exhibit strong spatial structure and there is
evidence for divergent selection at this locus in samples collected from
the Bering Sea region. The potential for adaptation to different thermal
regimes is particularly relevant given that Pacific cod have
demonstrated high natural mortality during recent ocean warming events.