title: Evolution of bidirectional sex change and gonochorism in fishes of the gobiid genera Trimma, Priolepis, and Trimmatom.
abstract: 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.
authors.affiliation: Laboratory of Fish Behavioral Ecology, Tateyama Station, Field Science Center, Tokyo University of Marine Science and Technology, 670 Banda, Tateyama, 294-0308, Japan. sunobe@biscuit.ocn.ne.jp.
authors.forename: Tomoki
authors.initials: T
authors.lastname: Sunobe
authors.affiliation: Department of Zoology, Natural History Museum and Institute, 955-2 Aoba-cho, Chuo-ku, Chiba, 260-8682, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Sado
authors.affiliation: Yokosuka City Museum, 95 Fukada-dai, Yokosuka, 238-0016, Japan.
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Hagiwara
authors.affiliation: Education Center, Kagoshima University, Korimoto, Kagoshima, 890-0065, Japan.
authors.forename: Hisaya
authors.initials: H
authors.lastname: Manabe
authors.affiliation: Kawanishi-Midoridai Senior High School, Koyodai, Kawanishi, Hyogo, 666-0115, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: Department of Fisheries, Faculty of Agriculture, Kindai University, Nara, 631-8505, Japan.
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Kobayashi
authors.affiliation: Kagoshima Immaculate Heart College, 4-22-1 Toso, Kagoshima, 890-8525, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakurai
authors.affiliation: Diving Service Umi-Annai, 7-7 Masagohonmachi, Kagoshima, 890-0067, Japan.
authors.forename: Shin-Ichi
authors.initials: SI
authors.lastname: Dewa
authors.affiliation: Faculty of Fisheries, Kagoshima University, Kagoshima, 890-0056, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Matsuoka
authors.affiliation: Faculty of Fisheries, Kagoshima University, Kagoshima, 890-0056, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Shinomiya
authors.affiliation: Laboratory of Fish Behavioral Ecology, Tateyama Station, Field Science Center, Tokyo University of Marine Science and Technology, 670 Banda, Tateyama, 294-0308, Japan.
authors.forename: Kazuya
authors.initials: K
authors.lastname: Fukuda
authors.affiliation: Department of Zoology, Natural History Museum and Institute, 955-2 Aoba-cho, Chuo-ku, Chiba, 260-8682, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Miya
mesh_terms: D000818:Animals; D005260:Female; D005399:Fishes / Q000033:anatomy & histology / Q000145:classification* / Q000235:genetics / Q000502:physiology*; D050259:Genes, Mitochondrial / Q000235:genetics; D008297:Male; D010802:Phylogeny; D012098:Reproduction / Q000276:immunology; D019849:Sex Determination Processes / Q000235:genetics / Q000502:physiology*; D012726:Sexual Behavior, Animal / Q000502:physiology
keywords: Bidirectional sex change; Gobiidae; Low-density model; Mating system; Phylogenetic analysis; Size-advantage model