Monogamous mating system and sexuality in the gobiid fish, Trimma marinae (Actinopterygii: Gobiidae)

The mating system and sexuality of the gobiid fish Trimma marinae were investigated in aquaria and by gonadal histological examination. The male to female sex ratio in the study aggregation was female-biased (14:27), and females were larger than males. T. marinae were monogamous because they established continuous pairs and spawned repeatedly with the same individuals. Observations of aggressive behavior suggested that the monogamous mating system resulted from female mate guarding. We also performed a rearing experiment to test whether sex change occurs in this species. As a result, none of the males or females reared separately in aquaria for 63 days changed sex. Additionally, gonadal histology revealed that mature fish had unisexual gonads (testis or ovary). These results strongly suggest that T. marinae is gonochoristic. However, immature fish had a bisexual gonadal structure, indicating juvenile hermaphroditism

Field observations on the feeding of the Nudibranch Gymnodoris spp. in Japan

Volume: 49Start Page: 91End Page: 9

Evolution of bidirectional sex change and gonochorism in fishes of the gobiid genera Trimma, Priolepis, and Trimmatom

Size-advantage and low-density models have been used to explain how mating systems favor hermaphroditism or gonochorism. However, these models do not indicate historical transitions in sexuality. Here, we investigate the evolution of bidirectional sex change and gonochorism by phylogenetic analysis using the mitochondrial gene of the gobiids Trimma (31 species), Priolepis (eight species), and Trimmatom (two species). Trimma and Priolepis formed a clade within the sister group Trimmatom. Gonadal histology and rearing experiments revealed that Trimma marinae, Trimma nasa, and Trimmatom spp. were gonochoric, whereas all other Trimma and Priolepis spp. were bidirectional sex changers or inferred ones. A maximum-likelihood reconstruction analysis demonstrated that the common ancestor of the three genera was gonochoristic. Bidirectional sex change probably evolved from gonochorism in a common ancestor of Trimma and Priolepis. As the gonads of bidirectional sex changers simultaneously contain mature ovarian and immature testicular components or vice versa, individuals are always potentially capable of functioning as females or males, respectively. Monogamy under low-density conditions may have been the ecological condition for the evolution of bidirectional sex change in a common ancestor. As T. marinae and T. nasa are a monophyletic group, gonochorism should have evolved from bidirectional sex change in a common ancestor