Zubizarreta, L. | bioRxiv Science

bioRxiv2020

The estrogenic pathway modulates non-breeding female aggression in a teleost fish

Aggressive behaviors are widespread among animals and are critical in the competition for resources. The physiological mechanisms underlying aggression have mostly been examined in breeding males, in which gonadal androgens, acting in part through their aromatization to estrogens, have a key role. There are two alternative models that contribute to further understanding hormonal mechanisms underlying aggression: aggression displayed in the non-breeding season, when gonadal steroids are low, and female aggression. In this study we approach, for the first time, the modulatory role of estrogens and androgens upon non-breeding aggression in a wild female teleost fish. We characterized female aggression in the weakly electric fish Gymnotus omarorum and carried out acute treatments 1 h prior to agonistic encounters with either an aromatase inhibitor or an antagonist of androgen receptors. Aromatase inhibition caused a strong distortion of aggressive behavior whereas anti-androgen treatment had no effect on behavior. Territorial non-breeding aggression in female G. omarorum is robust and depended on rapid estrogen actions to maintain high levels of aggression, and ultimately reach conflict resolution from which dominant/subordinate status emerged. Our results taken together with our own reports in males and the contributions from non-breeding aggression in bird and mammal models, suggest a conserved strategy involving fast-acting estrogens in the control of this behavior across species. In addition, further analysis of female non-breeding aggression may shed light on potential sexual differences in the fine tuning of social behaviors. HighlightsO_LIFemale Gymnotus omarorum displayed robust territorial aggression in lab settings. C_LIO_LIAcute treatment with aromatase inhibitor lowered aggression levels. C_LIO_LIAromatase inhibition increased first attack latency and decreased conflict resolution. C_LIO_LIAcute treatment with anti-androgens showed no effects. C_LIO_LIThis is the first report of estrogens underlying teleost non-breeding female aggression. C_LI

animal behavior and cognition↗

bioRxiv2020

Seasonal and social factors associated with spacing in a wild territorial electric fish

The expression of territorial behavior in wild species is especially suited to explore how animals integrate individual traits with dynamic environmental and social contexts. In this study, we focused on the seasonal variation of the determinants of territory size in the weakly electric fish Gymnotus omarorum. This species is a seasonal breeder that displays year-long territorial aggression, in which female and male dyads exhibit indistinguishable non-breeding territorial agonistic behavior and the only significant predictor of contest outcome is body size. We carried out field surveys across seasons that included the identification of individual location, measurements of water physico-chemical variables, characterization of individual morphometric and physiological traits, and their correlation to spatial distribution. Although Gymnotus omarorum tolerates a wide range of dissolved oxygen concentration, territory size correlated with dissolved oxygen in both seasons. In the non-breeding season, we show that territory size is sexually monomorphic and explained only by body size. In the breeding season, while body size no longer correlated with territory size, evidence of sexual differences in territory size determinants emerged. First, the overall spatial arrangement adopted a sexual bias. Second, territory size depended on gonadal hormones in both sexes, which was expected for males, but not previously reported in females. Third, females territory size correlated with gonadal size and females showed relatively larger territories than males, probably to meet sexually dimorphic energetic requirements. This study provides evidence of seasonal changes in factors correlated with territory size and contributes to the understanding of the mechanisms underlying behavioral plasticity.

animal behavior and cognition↗