Identification of male-specific markers by 2b-RAD sequencing reveals an XX/XY sex-determination system in cultured lined seahorse, Hippocampus erectus

Abstract

Seahorses (Hippocampus spp.), a group of male ovoviviparous fish, are of high commercial value in traditional Chinese medicine and aquarium trades. The lined seahorse (Hippocampus erectus), an easily domesticated species, was introduced to China and quickly became a popular farmed species to relieve the conflict between supply and demand. Although the sexual dimorphism in size and immunocompetence has been observed, the sex determination mechanism in the lined seahorse remains unclear. In the present study, we applied the 2b-RAD-seq approach for the first time to successfully identify 6 male-specific tags and 4 sex-specific SNP loci in the lined seahorse, which were further validated in 108 individuals by PCR amplification based on the flanking sequences of sex-specific markers. The male-specific tags and heterozygous SNP loci indicate that a male heterozygous XX/XY sex-determination system is employed in the lined seahorse. Based on the annotation and analysis of the sex-specific sequences, two sex-related candidate genes, lrriq1 and il34, were identified. The results provide novel insights into sex-determination mechanisms and promising methods for all-male breeding of Hippocampus erectus.