From the tropics to the pole and back again: Radiation in the flathead fishes (Platycephalidae) across Australia and the Indo‐West Pacific

Abstract

AbstractAimTo develop a comparative phylogeographic framework to understand the origins, evolution, taxonomic richness, and distribution of Australian demersal fish endemics in the context of the Indo‐West Pacific (IWP).LocationSouthern Australia and the IWP.TaxonPlatycephalidae (flathead fishes).MethodsNuclear and mitochondrial phylogenies of flathead fishes were inferred from 46 of 85 nominal species, and 14 additional cryptic species‐level lineages, representing 17 of the 18 genera. Molecular clocks and habitat trait reconstructions were used to infer the palaeoclimatic and geological events responsible for shaping the evolution and diversification of the group.ResultsThe family Platycephalidae comprises two sister subfamilies; Platycephalinae and Onigociinae, which diverged in the Eocene into predominantly temperate and tropical assemblages respectively. The basal platycephalin taxa are confined to southern Australia with the most derived groups in the tropics, following a high‐ to low‐latitudinal evolutionary trajectory. In contrast, the onigociins are predominantly associated with the tropics, and have diversified across the region since the early Miocene with very few introductions into temperate Australia.Main conclusionsPlatycephalinae and Onigociinae show contrasting evolutionary scenarios. Platycephalins have a temperate to tropical evolutionary trajectory consistent with their arrival into the region via tectonic rafting and subsequent dispersal. This dispersal was likely facilitated by formation of shallow‐water environments along the Sunda Arc margin following collision of the Australian and Eurasian Plates. In contrast, the Onigociinae has likely maintained a tropical presence across the IWP since the Eocene and has experienced higher diversification rates leading to circa three times the species diversity found in the Platycephalinae. Rounds of dispersal and allopatric speciation have subsequently played out across both low and high latitudes with both subfamilies harbouring cryptic species‐level lineages. This work provides an explicit working hypothesis for exploring origins and diversification in other demersal fishes endemic to the Australian continent.