Genomic and life-history discontinuity reveals a precinctive lineage for a deep-water grouper with gene flow from tropical to temperate waters on the west coast of Australia

Abstract

We address a critical knowledge gap for the Eightbar Grouper, Hyporthodus octofasciatus, one of the largest groupers targeted in mostly tropical, deep-water fisheries, using genetic analyses of mitochondrial DNA (mtDNA; N = 248) and age and growth information (N = 727) from specimens collected from the eastern Indian Ocean to the western central Pacific Ocean. We additionally used a genotype-by-sequencing approach on a subset of these samples (N = 94) to determine the extent of egg and larval dispersal between tropical and temperate regions along the west coast of Australia (WA). Discontinuity in mtDNA and nuclear genomes, and marked variation in growth trajectories and longevity revealed a distinct, non-interbreeding cryptic lineage in WA. The WA lineage appears to be geographically isolated from the oceanic Indo-West Pacific (IP) lineage and precinctive to a single continuous coastline from tropical to temperate waters (covering > 2200 km and ∼20° of latitude). The Hyporthodus phylogeny reveals a possible allopatric speciation scenario with sister lineages endemic to the east (i.e. H. ergastularius) and west (i.e. WA lineage of H. octofasciatus) coasts of Australia, each diverging from a broader IP distributed ancestor (i.e. IP lineage of H. octofasciatus) in the early Pleistocene Epoch. Sustainable management of these species therefore needs to consider their evolutionary distinction, in addition to aspects of their life-history strategies and limited geographic distribution that infers high vulnerability to fishing at relatively low levels of exploitation.