Molecular phylogeny and patterns of diversification in syngnathid fishes

Hamilton and Saarman et al. molecular phylogeny and patterns of diversification in syngnathid fishes. [Display omitted] •Expanded taxonomic and genetic sampling reveals new patterns of syngnathid evolution.•Molecular patterns suggest convergence in traditional morphological characters.•Complex brood pouches, prehensile tails, and pygmy morphology evolved multiple times.•Biogeographic patterns reveal multiple drivers of evolutionary diversification.•Two subfamilies are formally recognized and further taxonomic revisions are required. The family Syngnathidae is a large and diverse clade of morphologically unique bony fishes, with 57 genera and 300 described species of seahorses, pipefishes, pipehorses, and seadragons. They primarily inhabit shallow coastal waters in temperate and tropical oceans, and are characterized by a fused jaw, male brooding, and extraordinary crypsis. Phylogenetic relationships within the Syngnathidae remain poorly resolved due to lack of generic taxon sampling, few diagnostic morphological characters, and limited molecular data. The phylogenetic placement of the threatened, commercially exploited seahorses remains a topic of intense interest, with conflicting topologies based on morphology and predominantly mitochondrial genetic data. In this study, we integrate eight nuclear and mitochondrial markers and 17 morphological characters to investigate the phylogenetic structure of the family Syngnathidae at the generic level. We include 91 syngnathid species representing 48 of the 57 recognized genera, all major ocean basins, and a broad array of temperate and tropical habitats including rocky and coral reefs, sand and silt, mangroves, seagrass beds, estuaries, and rivers. Maximum likelihood and Bayesian analyses of 5160bp from eight loci produced high congruence among alternate topologies, defining well-supported and sometimes novel clades. We present a hypothesis that confirms a deep phylogenetic split between lineages with trunk- or tail-brood pouch placement, and provides significant new insights into the morphological evolution and biogeography of this highly derived fish clade. Based on the fundamental division between lineages - the tail brooding “Urophori” and the trunk brooding “Gastrophori” - we propose a revision of Syngnathidae classification into only two subfamilies: the Nerophinae and the Syngnathinae. We find support for distinct principal clades within the trunk-brooders and tail-brooders, the latter of which include sea