Background/Aims: Acanthistius paxtoni, the Orangelined Wirrah, is a species of marine, rocky reef associated fish. Described in 1982 based on two specimens, it has never been observed, collected or recorded since. They are characterised by prominent orange spots and striations, six dark vertical cross bars and are easily distinguishable from their east Australian relatives. Despite this, the rarity of A. paxtoni has yet to be explained. Also, the evolutionary relationships of A. paxtoni remain uncertain and have resisted previous attempts at resolution. Previously, we hypothesised that A. paxtoni is the hybrid offspring of the two other east Australian species of Acanthistius, A. ocellatus and A. cinctus, based on their intermediate morphology. However, Sanger sequencing of the two formalin-fixed type specimens produced no viable genetic evidence to support this. The aim of this study is to definitively resolve the identity of Acanthistius paxtoni.
Methods: In this study, we use shotgun sequencing and assemble whole mitochondrial genomes and nuclear markers from both specimens. In addition, we also compare the morphology and osteology of Acanthistius paxtoni with that of the potential parents, ensuring this is an integrative approach.
Results: We find pairwise distances of approximately 1% between the mitochondrial genomes of Acanthistius paxtoni and the unexpected maternal parent. Furthermore, nuclear markers indicate substantial evidence of backcrossing. We also find that the specimens of A. paxtoni share key morphological and osteological characters with both parent species.
Conclusion: We confirm that Acanthistius paxtoni is indeed the result of hybridisation, but between an unexpected pair of parents, and explore the mechanisms of a hybridisation event that extends the known limits of hybridisation in perciform fishes.