INTRASEXUAL AGGRESSION IN CICHLIDS: CAN ESTROGENS BE CONSIDERED AS KEY ELEMENTS OF THE CHALLENGE HYPOTHESIS?

MARÍA FLORENCIA SCAIA; LEONEL MORANDINI; VANCE TRUDEAU; GUSTAVO SOMOZA; MATÍAS PANDOLFI

Manaos

Congreso; Reproductive Physiology of Fish; 2018

IntroductionIt has been historically suggested that aggressive behavior in males is mediated by androgens, but recent evidence suggests that the key step regulating this behavior is the aromatization to estrogens. The challenge hypothesis suggests that behavioral interactions lead to an increase in plasma androgen levels in response to social instability, but there is no evidence regarding estradiol levels. Despite the fact that females also display aggressive behavior, this framework has been focused mainly on males and the physiological regulation of female aggression is still understudied. The first aim of this study was to determine whether there is a relationship between sex steroids and intrasexual aggression in males and females of Cichlasoma dimerus, a monogamous Neotropical cichlid with bi-parental behavior. Moreover, the second aim of this study was to evaluate if our data supports the challenge hypothesis for both sexes and to determine if estrogens also increase as a consequence of social instability. MethodsA total of 18 females and 16 males were used for intrasexual dyadic agonistic encounters. Blood samples were obtained before and after each encounter by puncture of the caudal vein to measure steroid hormone levels pre and post conflict. All agonistic interactions in the contest were recorded during one hour and measures of total aggression and submission of each animal were calculated to characterize winners and losers. After trials, fish were euthanized; gonads were dissected, weighted and used to calculate the gonadosomatic index. Plasma testosterone (T), 11-ketotestosterone (11-KT) and estradiol (E2) were determined with commercial ELISA kits.Results and DiscussionWinner females, but not males, had higher plasma E2 levels than losers before the contest (2.2-fold increase, p=0.046), suggesting that initial E2 levels could predict the winner status in females. However, there were no differences in androgen levels in neither sex. During male encounters there was not only a 5.4 and 3.2-fold increase in T and 11-KT, but also 1.5-fold increase in E2 levels (p=0.016, p=0.018, p=0.023, respectively), linking the challenge hypothesis to estrogens. Sex steroids did not increase in response to the dyadic encounter in females and this delta E2 did not correlate with their GSI, suggesting that changes in E2 in females did not depend on their reproductive status.ConclusionThese results suggest that in this context initial estrogens can predict the outcome of the encounter in females. Moreover, this is the first evidence suggesting that the challenge hypothesis could be referred to estrogens.