Interspecific hybridization in seahorses: artificially produced hybrid offspring of Hippocampus kuda and Hippocampus reidi

Sang-Yun Han,Gyeong Eon Noh,Jin-Koo Kim,Sum Rho

doi:10.1186/s41240-018-0088-x

Abstract

Interspecific hybridization experiments were conducted between the common seahorse Hippocampus kuda (male) and the slender seahorse H. reidi (female) during artificial rearing to develop a new aquarium fish with unique polyandrous mating. Molecular analysis via mitochondrial DNA (mtDNA) cytochrome b and nuclear DNA (ncDNA) ribosomal protein S7 gene supported the hybridization between the two species, and the hybrid also showed morphological characteristics of both species. Juveniles of H. kuda have dense melanophores on the whole body or only on the trunk and tail, whereas juveniles of H. reidi have thin melanophores on the whole body or present in stripes only along their prominent trunk and tail rings. However, all the hybrid juveniles had dense melanophores only on the tail, with the striped trunk rings, thus showing an intermediate pattern, and these patterns were limited to the fairly early stage of development (1–10 days old). In contrast, the two eye spines in the hybrid were apparent after 9 days old, which were not inherited from H. kuda (one eye spine), but from H. reidi (two eye spines). According to LOESS (local regression) analysis, the growth rate increased between 20 and 25 days, and the hybrids grew faster than H. kuda when they entered the explosive second phase of growth between 25 and 45 days for all the seahorses. This study highlights the hybridization between H. kuda and H. reidi may contribute to the improved taxonomic information of young seahorses.

Highlights

The genus Hippocampus includes 41 species throughout the world (Lourie et al 2016)
We derived age–standard length (SL) relational expression and allometric relational expression (SL–head length (HL), SL–trunk length (TrL), SL– tail length (TaL), SL–snout length (SnL), SL–snout depth (SnD), SL–head depth (HD), SL–Dorsal fin base length (DfL), SL–Pectoral fin base length (PfL), and SL– eye diameter (ED)) using Local regression (LOESS) curves in ggplot2 package of R software ver. 3.3.1 (Jacoby 2000; Wickham 2009; R Core Team 2017), and we examined the differences in the growth patterns of the seahorses by LOESS, a nonparametric approach of simple polynomial regression represented by a moving average
H. kuda has dense melanophores on its whole body or only on the trunk and tail, whereas the juveniles of H. reidi have thin melanophores or a striped pattern and the melanophores only occur on their prominent trunk and tail rings (Fig. 2b; see Choo and Liew 2006; Mai and Loebmann 2009; Van Wassenbergh et al 2009)

Summary

Introduction

The genus Hippocampus includes 41 species throughout the world (Lourie et al 2016). Some populations are mature at 7 cm in standard length (SL), whereas others grow to 17 cm SL. Their color varies: yellow, sandy, or white, but usually black, with a grainy texture or dark spots. H. reidi (slender seahorse) is distributed along the western Atlantic coast, their reproductive rates are low and their home ranges limited, H. kuda and H. reidi are generally valuable seahorse species, with worldwide market demand, which may cause their overexploitations and threaten natural populations through the undoubted pressure of the activities of fisheries that supply the market (Vincent 1996; Lourie et al 1999).

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Discussion

Conclusion