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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.

Closely related species can provide valuable insights into evolutionary processes through comparison of their ecology, geographic distribution and the history recorded in their genomes. In the Indo-Pacific, many reef fishes are divided into sister species that come into secondary contact at biogeographic borders, most prominently where Indian Ocean and Pacific Ocean faunas meet. It is unclear whether hybridization in this contact zone represents incomplete speciation, secondary contact, an evolutionary dead-end (for hybrids) or some combination of the above. To address these issues, we conducted comprehensive surveys of two widely-distributed surgeonfish species, Acanthurus leucosternon (N=141) and A. nigricans (N=412), with mtDNA cytochrome b sequences and ten microsatellite loci. These surgeonfishes are found primarily in the Indian and Pacific Oceans, respectively, but overlap at the Christmas and Cocos-Keeling Islands hybrid zone in the eastern Indian Ocean. We also sampled the two other Pacific members of this species complex, A. achilles (N=54) and A. japonicus (N=49), which are known to hybridize with A. nigricans where their ranges overlap. Our results indicate separation between the four species that range from the recent Pleistocene to late Pliocene (235,000-2.25million years ago). The Pacific A. achilles is the most divergent (and possibly ancestral) species with mtDNA dcorr≈0.04, whereas the other two Pacific species (A. japonicus and A. nigricans) are distinguishable only at a population or subspecies level (ΦST=0.6533, P

The regal angelfish (Pygoplites diacanthus; family Pomacanthidae) occurs on reefs from the Red Sea to the central Pacific, with an Indian Ocean/Rea Sea color morph distinct from a Pacific Ocean morph. To assess population differentiation and evaluate the possibility of cryptic evolutionary partitions in this monotypic genus, we surveyed mtDNA cytochrome b and two nuclear introns (S7 and RAG2) in 547 individuals from 15 locations. Phylogeographic analyses revealed four mtDNA lineages (d=0.006-0.015) corresponding to the Pacific Ocean, the Red Sea, and two admixed lineages in the Indian Ocean, a pattern consistent with known biogeographic barriers. Christmas Island in the eastern Indian Ocean had both Indian and Pacific lineages. Both S7 and RAG2 showed strong population-level differentiation between the Red Sea, Indian Ocean, and Pacific Ocean (ΦST=0.066-0.512). The only consistent population sub-structure within these three regions was at the Society Islands (French Polynesia), where surrounding oceanographic conditions may reinforce isolation. Coalescence analyses indicate the Pacific (1.7Ma) as the oldest extant lineage followed by the Red Sea lineage (1.4Ma). Results from a median-joining network suggest radiations of two lineages from the Red Sea that currently occupy the Indian Ocean (0.7-0.9Ma). Persistence of a Red Sea lineage through Pleistocene glacial cycles suggests a long-term refuge in this region. The affiliation of Pacific and Red Sea populations, apparent in cytochrome b and S7 (but equivocal in RAG2) raises the hypothesis that the Indian Ocean was recolonized from the Red Sea, possibly more than once. Assessing the genetic architecture of this widespread monotypic genus reveals cryptic evolutionary diversity that merits subspecific recognition. We recommend P.d. diacanthus and P.d. flavescens for the Pacific and Indian Ocean/Red Sea forms.