A new multi-locus timescale reveals the evolutionary basis of diversity patterns in triggerfishes and filefishes...

Balistoid fishes (triggerfishes, filefishes, leatherjackets) represent one of the most successful radiations of tetraodontiform fishes across the world's oceans. Balistids (triggerfishes) are largely circumtropical in coral reef environments while most monacanthids (filefishes, leatherjackets) are distributed across reef and non-reef habitats in the Indo-western Pacific. Although members of these clades share a distinctive mode of locomotion that relies upon coordinated oscillation or undulation of enlarged dorsal and anal fins, species richness as well as morphologial and ecological diversity are generally considered to be higher in monacanthids than in triggerfishes. Explicit evolutionary comparisons of diversity patterns between these sister clades have been hampered by the paucity of systematic studies of filefishes relative to triggerfishes. Furthermore, a well-sampled molecular timescale for balistoids is lacking, hindering our understanding of the evolutionary history of these fishes. Here, we produce the largest balistoid molecular dataset to date, based on two mitochondrial and three nuclear loci, for a total of 86 species, and we time-calibrate it using three tetraodontiform fossils. We show that several of the traditional monacanthid genera are not monophyletic and that the balistid Xenobalistes tumidipectoris is nested within the genus Xanthichthys, and suggest that the generic name Xenobalistes be dissolved. Our timetree reveals a Late Miocene origin of balistids, in accordance with previous studies, but a Late Eocene age for the crown monacanthids, which experienced significant diversification during the Late Oligocene and Early Miocene. Comparative analyses reveal no significant family-level differences in rates of speciation or body size evolution, suggesting that the greater diversity of filefishes can be attributed to their more ancient crown age compared to triggerfishes.