Complete mitochondrial genomes of eight seahorses and pipefishes (Syngnathiformes: Syngnathidae): insight into the adaptive radiation of syngnathid fishes

Abstract

Background The evolution of male pregnancy is the most distinctive characteristic of syngnathids, and their specialized life history traits make syngnathid species excellent model species for many issues in biological evolution. However, the origin of syngnathids and the evolutionary divergence time of different syngnathid species remain poorly resolved. Comprehensive phylogenetic studies of the Syngnathidae will provide critical evidence to elucidate their origin, evolution, and dispersal patterns. Results We sequenced the mitochondrial genomes of eight syngnathid species in this study, and the estimated divergence times suggested that syngnathids diverged from other teleosts approximately 48.8 Mya during the Eocene period. Selection analysis showed that many mitochondrial genes of syngnathids exhibited significantly lower Ka/Ks values than those of other teleosts. The two most frequently used codons in syngnathid fishes were different from those in other teleosts, and a greater proportion of the mitochondrial simple sequence repeats (SSRs) were distributed in non-coding sequences in syngnathids compared with other teleosts. Conclusions Our study indicated that syngnathid fishes experienced an adaptive radiation process during the early explosion of species. Syngnathid mitochondrial OXPHOS genes appear to exhibit depressed Ka/Ks ratios compared with those of other teleosts, and this may suggest that their mitogenomes have experienced strong selective constraints to eliminate deleterious mutations. Electronic supplementary material The online version of this article (10.1186/s12862-019-1430-3) contains supplementary material, which is available to authorized users.

Complete mitochondrial genome and phylogenetic analysis of the Gray’s pipefish Halicampus grayi Kaup 1856

“…The high A + T content bias (59.28%) was basically consistent with those of other syngnathid fishes (Wang et al. 2019 ). The mitogenome of H. grayi , in total, contained 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA genes, and a control region.…”

“…The complete mitochondrial genome of H. grayi was 16,959 bp in length with the overall base compositions of 30.03, 29.25, 24.54, and 16.17% for A, T, C, and G, respectively. The high A þ T content bias (59.28%) was basically consistent with those of other syngnathid fishes (Wang et al 2019). The mitogenome of H. grayi, in total, contained 13 protein-coding genes (PCGs), 22 tRNA genes, 2 rRNA genes, and a control region.…”

The evolution and physiology of male pregnancy in syngnathid fishes

“…This analysis is the most complete syngnathid phylogeny to date, and includes almost one third of all syngnathids (91 species; 84% of described genera) (Hamilton et al ., ). The tree topology, based on sequences for four nuclear genes, is in strong agreement with morphological data as well as phylogenies constructed using complete mitochondrial genomes of eight species (Wang et al ., ), and a syngnathiform phylogeny constructed using ultraconserved elements (Longo et al ., ).…”

Complete mitochondrial genome of nearly threatened freshwater ornamental fish, Microphis deocata and its phylogenetic relationship within Syngnathidae

“…The Syngnathids differ from other vertebrates by exhibiting 'male pregnancy' (St€ olting and Wilson 2007). They have an extended body covered with armour of bony plates in place of scales, elongated snout and fused jaws (Wang et al 2019). Due to specialized morphology, the fish is a popular aquarium fish with enormous demand.…”