Molecular phylogeny and patterns of diversification in syngnathid fishes

Abstract

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 seahorses, seadragons, independent lineages of pipehorses, and clades that originated in southern Australia and the Western Atlantic. We suggest the seahorse genus Hippocampus is of Indo-Pacific origin and its sister clade is an unexpected grouping of several morphologically disparate Indo-Pacific genera, including the Pacific pygmy pipehorses. Taxonomic revision is required for multiple genera, particularly to reflect deep evolutionary splits in nominal lineages from the Atlantic versus the Indo-Pacific.

Estimating population parameters of longsnout seahorses, Hippocampus reidi (Teleostei: Syngnathidae) through mark-recapture

“…Pipefishes, pipehorses, seahorses and seadragons belong to the Syngnathidae family, which comprises around 300 species of characteristic long-snouted fish with fused jaws and male brooding, inhabiting temperate and tropical coastal waters (Hamilton et al, 2017). The mark-recapture approach has been successfully employed to study life history traits, behavior and movement patterns of some of these species (e.g.…”

Hippocampus japapigu, a new species of pygmy seahorse from Japan, with a redescription of H. pontohi (Teleostei, Syngnathidae)

“…111770). DNA extraction, PCR amplification, alignment, and analysis of COI sequence was performed following protocols described in Hamilton et al (2017). Genetic distances (uncorrected p -distances) were calculated based on COI using MEGA v. 7.0.26 (Kumar et al 2017).…”

“…material 1 shows genetic distance analysis at the COI gene (uncorrected p distances) between H.japapigu and previously sequenced non-type specimens of the pygmy seahorses H.pontohi , H.bargibanti , and H.denise (Hamilton et al 2017), and additional vouchered specimens of H.pontohi . Hippocampusjapapigu differs from H.pontohi by 10.1%, from H.bargibanti by 13.0%, and H.denise by 10.1%.…”

“…While one species, H.bargibanti Whitley, 1970, was described in 1970, all other species have been described since 2000. Most are known from very few specimens and only three species have been analyzed genetically (Hamilton et al 2017). Six pygmy seahorse species are currently recognized and documented throughout the central Indo-Pacific, ranging from the Coral Triangle, West Pacific, Australia, to central Japan: H.bargibanti , H.denise Lourie & Randall, 2003, H.colemani Kuiter, 2003, H.pontohi Lourie & Kuiter, 2008, H.satomiae Gomon & Kuiter, 2009, and H.waleananus Gomon & Kuiter, 2009 (Whitley 1970; Kuiter 2003; Lourie and Randall 2003; Senou et al 2006, 2007, 2008; Baine and Harasti 2007; Lourie and Kuiter 2008; Motomura et al 2010; Allen and Erdmann 2012; Smith et al 2012).…”

Systematic relationships of sympatric pipefishes (Syngnathus spp.): A mismatch between morphological and molecular variation

“…Whereas diversity of syngnathids is highest around southern Australia and the Indo‐Pacific Ocean, only few lineages are found in the eastern Pacific Ocean making this biogeographic region markedly species poor (Hamilton et al, ; Kuiter, ). Atypically, Syngnathus contains only two recognised species in the western Pacific Ocean, Syngnathus schlegeli Kaup 1853 and Syngnathus chihiroe Matsunuma , but a total of eight Syngnathus spp.…”