Endocrine control of sexual behavior in sneaker males of the peacock blenny Salaria pavo: Effects of castration, aromatase inhibition, testosterone and estradiol

Abstract

The effects of castration and sex steroid manipulations on the expression of sexual behavior were investigated in a small fish, the peacock blenny, Salaria pavo. In this species, large males defend nests and attract females while small "sneaker" males reproduce by imitating the female morphology and courtship behavior in order to approach nests during spawning events and parasitically fertilize eggs. Sneakers switch into nest holders in their second breeding season, thus displaying both male and female-like sexual behavior during their lifetime. We tested the effects of castration and of an aromatase inhibitor (Fadrozole, F), testosterone (T) or 17β-estradiol (E 2 ) implants on the expression of male and female-like behavior in sneakers. Sneakers were either sham-operated, castrated or castrated and implanted with vehicle, F, T + F or E 2 + F. Seven days after the treatment, sneakers were placed in a tank with a nesting male, two ripe females and an available nest. Castrated fish had lower levels of circulating T and increased the time spent displaying female typical nuptial coloration. T implants had the opposite effect, inhibiting the expression of femalelike behavior and coloration. E 2 implants had no significant effect on the display of sexual behavior but the frequency of aggressive displays decreased. The results agree with previous findings in sneakers of S. pavo that demonstrated an inhibition of female-like behavior by 11-ketotestosterone (11-KT). The reported increase in T and 11-KT production when sneakers change into nest holders may thus contribute to behaviorally defeminize sneakers. Contrarily, both T and E 2 failed to promote male-like behavior, suggesting that behavioral masculization during tactic switching depends on other neuroendocrine mechanisms or that the time length of the experiment was insufficient to induce male-like behavioral changes in sneakers.

Brain aromatase mRNA expression in two populations of the peacock blenny Salaria pavo with divergent mating systems

“…Administration of both T and 11KT to parasitic males decreases the frequency of the female-like sexual displays and promotes the development of male secondary sexual characters (Gonçalves et al, 2007;Oliveira et al, 2001). This is consistent with the fact that circulating levels of both T and 11KT are higher in nesting males than in parasitic males , and in fish species with male ART higher levels of 11KT (but not T) have consistently been found in nesting males (Brantley et al, 1993;Oliveira, 2006).…”

“…In S. pavo, levels of both 11KT and T are higher in nesting males , and, in general, in species with male ART nesting males have higher levels of 11KT, a non-aromatizable androgen, but not of T when compared with parasitic males (Brantley et al, 1993;Oliveira, 2006). The administration of both T and 11KT to parasitic males inhibited the expression of female-like displays, although it did not induce malelike sexual behaviors (Gonçalves et al, 2007;Oliveira et al, 2001). Those experiments only lasted for 8 days and it is possible that a longer time frame would be necessary for the putative masculinizing behavioral effects of androgens to be observed.…”

“…The absence of interpopulational differences in brain aromatase levels is more unexpected for females than for parasitic males. Estradiol administration to parasitic males from Ria Formosa had no effect in the female-like displays (Gonçalves et al, 2007) and thus interpopulational differences are likely to be regulated by other neuroendocrine agents. Also, both female and parasitic female-like courtship behaviors in S. pavo have been shown to depend on the action of the brain neuropeptide arginine vasotocin (AVT), the fish homologous of the mammalian arginine vasopressin (AVP).…”

“…Estrogens have been shown to reduce aggression in fish (e.g., Bell, 2001;Munro and Pitcher, 1983) and increases in aggression were negatively correlated with brain aromatase activity in a sex-changing goby (Black et al, 2005). Importantly, E 2 administration to parasitic males of S. pavo from the Ria Formosa population was also shown to inhibit aggression (Gonçalves et al, 2007). Thus, the higher brain aromatase levels in males from Ria Formosa probably increase local E 2 synthesis and this may induce the necessary decrease in aggression due to the scarceness and aggregated nature of the available nests.…”

Intra- and interspecific aggression do not modulate androgen levels in dusky gregories, yet male aggression is reduced by an androgen blocker

“…During these periods, higher levels of androgen are likely to be produced by the enlarged gonads and further hormonal manipulations might elucidate whether such changes in steroids lead to sex specific differences in territory defense, and the associated different behavioral tactics (e.g. Gonçalves et al, 2007).…”