Genetic Variations in Two Seahorse Species (Hippocampus mohnikei and Hippocampus trimaculatus): Evidence for Middle Pleistocene Population Expansion

Abstract

Population genetic of seahorses is confidently influenced by their species-specific ecological requirements and life-history traits. In the present study, partial sequences of mitochondrial cytochrome b (cytb) and control region (CR) were obtained from 50 Hippocampus mohnikei and 92 H. trimaculatus from four zoogeographical zones. A total of 780 base pairs of cytb gene were sequenced to characterize mitochondrial DNA (mtDNA) diversity. The mtDNA marker revealed high haplotype diversity, low nucleotide diversity, and a lack of population structure across both populations of H. mohnikei and H. trimaculatus. A neighbour-joining (NJ) tree of cytb gene sequences showed that H. mohnikei haplotypes formed one cluster. A maximum likelihood (ML) tree of cytb gene sequences showed that H. trimaculatus belonged to one lineage. The star-like pattern median-joining network of cytb and CR markers indicated a previous demographic expansion of H. mohnikei and H. trimaculatus. The cytb and CR data sets exhibited a unimodal mismatch distribution, which may have resulted from population expansion. Mismatch analysis suggested that the expansion was initiated about 276,000 years ago for H. mohnikei and about 230,000 years ago for H. trimaculatus during the middle Pleistocene period. This study indicates a possible signature of genetic variation and population expansion in two seahorses under complex marine environments.

DNA barcoding reflects the diversity and variety of brooding traits of fish species in the family Syngnathidae along China’s coast

“…Clear species identification will facilitate augmenting fishing practices, designing protective marine reserves, and assessing the captive breeding potential for seahorses. Our work shows that China has at least 10 species of seahorses along the country's coast; previous studies cited only four: H. kuda, H. mohnikei, H. spinosissimus, and H. trimaculatus (Lin et al, 2006;Lourie et al, 2005;Zhang et al, 2014).…”

“…Biological mechanisms, water dynamics (such as ocean currents), geographic distance, and historical events may play important roles in the population genetic structures of marine species (Barber et al, 2000;Nelson et al, 2000;Saarman et al, 2010). Many marine fish lack a phylogeographic structure and show genetic homogeneity within populations (Friess and Sedberry, 2011; Zhang et al, 2014). In this study, some intraspecific genetic variations were reduced to 0.15% when comparing individuals from distant localities.…”

“…China has a long distance coastline, and the constant ocean area along the mainland crosses an oriental zone, warm-temperature zone, and tropical zone (Briggs, 1995), which leads to wide distributions and abundances for some fish of the family Syngnathidae (Zhang et al, 2014). In the present study, we applied DNA barcoding for the identification of this group of fish along China's coast, which is regarded as an important branch of the marine biodiversity center of the Indo-West Pacific Ocean (Barber et al, 2000).…”

Direct observation of drifting juvenile seahorse Hippocampus trimaculatus (Leach, 1814) beneath the offshore surface at Malacca Strait

“…In this study, one of the H. trimaculatus specimens possesses a brood pouch, but it was considered as a juvenile since its height was less than 120 mm, according to Yip et al (2015). Although seahorses are not active swimmers, it has been suggested that H. trimaculatus species may have a high dispersal capability and undergo habitat shift or translocation , Zhang et al 2014). The direct observations of H. trimaculatus juveniles near to surface (< 0.1 m) of deep water in this study was likely the first drifting juvenile seahorse ever recorded along Malacca Strait and this could be a strong evidence for the passive long-distance migration in young H. trimaculatus.…”

“…Seahorses are known to have wide geographical distributions; however, most populations show low genetic diversity, which is probably because these populations descend from a limited number of founders (Teske et al 2005, Woodall et al 2011, Zhang et al 2014). This phenomenon is probably linked to their poor mobility trait, since all seahorses do not have caudal fins, but do have prehensile tails which allow them to cling on holdfast or bottom substrate (Lourie et al 2004, Curtis andVincent 2006).…”