Male-predominant galanin mediates androgen-dependent aggressive chases in medaka

Abstract

Recent studies in mice demonstrate that a subset of neurons in the medial preoptic area (MPOA) that express galanin play crucial roles in regulating parental behavior in both sexes. However, little information is available on the function of galanin in social behaviors in other species. Here, we report that, in medaka, a subset of MPOA galanin neurons occurred nearly exclusively in males, resulting from testicular androgen stimulation. Galanin-deficient medaka showed a greatly reduced incidence of male–male aggressive chases. Furthermore, while treatment of female medaka with androgen induced male-typical aggressive acts, galanin deficiency in these females attenuated the effect of androgen on chases. Given their male-biased and androgen-dependent nature, the subset of MPOA galanin neurons most likely mediate androgen-dependent male–male chases. Histological studies further suggested that variability in the projection targets of the MPOA galanin neurons may account for the species-dependent functional differences in these evolutionarily conserved neural substrates.

Evolutionary differentiation of androgen receptor ohnologs is responsible for the development of androgen-dependent unique sexual characteristics in a teleost fish

“…Previous studies have shown that ar expression in the brain and the pituitary regulates the expression of several hormones that can control the reproduction and social behaviours in medaka 10,43,47 . Hence, we observed the mating behaviour of a test male (homozygotes for the WT, ara KO, arb KO, or DKO alleles) with a WT female.…”

“…Males perform courtship behaviours consisting of a sequence of stereotyped actions that are easily quantified 35,38,41 . Furthermore, previous studies demonstrated that Ars are expressed in the brain 42 and can control the sexually dimorphic expression of neuropeptides and biologically active nonapeptides 10,43 . Although these findings indicate that Ars are involved in a broad range of male-specific traits in medaka, the differential role of the two Ars remains unclear.…”

“…However, few empirical studies have investigated the molecular mechanisms underlying the evolutionary acquisition of diverse sexually dimorphic traits in vertebrates. Teleosts show unique sets of extreme sexual dimorphism 3 , such as an elongated median fin 4 , copulatory organs 5,6 , and nuptial coloration 7 , and behavioural traits including nest building 8 , courtship 9 , and aggressive acts 10 . Such male traits increase male reproductive success but often harm females because of the sexspecific fitness optima of these traits.…”

Gene family evolution underlies cell-type diversification in the hypothalamus of teleosts

“…We observed differences in the expression patterns of several neuropeptides associated with these behaviours in other systems. For example, decreased galn expression in cave-morphs versus surface-morphs could partially explain the loss of sleep or changes in appetite or aggression in cave-morphs [56][57][58] . Alterations in oxytocin cells might also be linked to changes in appetite, or the lack of social interactions (schooling) observed in cave-morphs 56,59 .…”

Establishment of open-source semi-automated behavioral analysis system and quantification of the difference of sexual motivation between laboratory and wild strains

“…So far, the majority of researchers have recorded the videos of animal behavior by using video camera and manually annotated the behavioral events while replaying the videos 5 – 11 . However, simultaneous video-recording inevitably tends to be associated with human-errors with increasing number of cameras.…”