Relationships between sex and the size and number of forebrain gonadotropin-releasing hormone-immunoreactive neurones in the ballan wrasse (Labrus berggylta), a protogynous hermaphrodite.
This study is the first to examine the brain gonadotropin-releasing hormone (GnRH) cell population phenotype in a protogynous and monandric sequentially hermaphroditic fish. Male ballan wrasse (Labrus berggylta) had on average higher numbers of GnRH-immunoreactive (GnRH-ir) cells within the brain preoptic area (POA) than females, a difference not found in GnRH-ir cells in other brain regions. Furthermore, in males, but not females, the number of these POA GnRH-ir cells correlated with body size. Maturational state (prespawning or postspawning) had marked effects on mean profile sizes (but not numbers) of both GnRH-ir cell bodies and cell nuclei, even when existing differences in body size and allometric relationships had been taken into account. Postspawning males tended to have larger GnRH-ir profiles in all brain regions relative to both prespawning males and females. Moreover, the GnRH-ir cell number in POA, and the cell body profile size in both POA and at the level of the anterior commissure, correlated with gonad size in spermiated prespawning males, indicating a relationship between both size and number of GnRH cells and male gonadal development. These results suggest that temporary changes in the size of brain GnRH-ir neurones are coupled to the male spawning cycle, and that permanent POA GnRH-ir cell number changes are involved in the process of sex change in sequential hermaphrodites. However, smaller males had no more preoptic GnRH-ir cells than equally sized females, which may argue against a proximate inducing role of GnRH cell number changes in naturally occurring sex reversal.
Evolution Biology Centre, Department of Limnology, Uppsala University, Sweden. ulf.elofsson@limno.uu.se
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Elofsson
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Winberg
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Nilsson
D000818:Animals; D002452:Cell Count; D002467:Cell Nucleus / Q000378:metabolism; D048429:Cell Size / Q000502:physiology; D005260:Female; D005399:Fishes / Q000033:anatomy & histology* / Q000378:metabolism / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D057850:Hermaphroditic Organisms; D007150:Immunohistochemistry; D008297:Male; D009474:Neurons / Q000166:cytology / Q000378:metabolism; D016548:Prosencephalon / Q000166:cytology / Q000378:metabolism*; D012727:Sex Characteristics; D019849:Sex Determination Processes / Q000503:physiopathology*; D014018:Tissue Distribution / Q000502:physiology
D007987:Gonadotropin-Releasing Hormone