Plasticity of the reproductive axis caused by social status change in an African cichlid fish: II. Testicular gene expression and spermatogenesis, Endocrinology

Social position inadominancehierarchy isoftentightly coupledwithfertility.Consequently,ananimal thatcanrecognizeandrapidlytakeadvantageofanopportunitytorise inrankwillhaveareproductive advantage.Reproduction inall vertebrates is controlledbythebrain-pituitary-gonadaxis, and inmales of theAfrican cichlid fishAstatotilapiaburtoni, GnRH1neurons at theapexof this axis areunder social control. However, little is known about how quickly social information is transformed into functional reproductive change, or about how socially controlled changes in GnRH1 neurons influence down-stream actions of the brain-pituitary-gonad axis. We created an opportunity for reproductively sup-pressed males to ascend in status and thenmeasured how quickly the perception of this opportunity caused changes inmRNAand protein levels of the pituitary gonadotropins.mRNA levels of the-sub-unitsofLHandFSHroserapidly inthepituitary30minafter suppressedmalesperceivedanopportunity to ascend. In contrast, mRNA levels of GnRH receptor-1 remained unchanged during social transition butwerehigher in stabledominant comparedwith subordinatemales. In thecirculation, levelsofboth LHandFSHwerealsoquicklyelevated.Therewasapositive correlationbetweenmRNAin thepituitary and circulating protein levels for LH and FSH, and both gonadotropinswere positively correlatedwith plasma 11-ketotestosterone. Our results show that the pituitary is stimulated extremely rapidly afte