A Teleost Fish Model to Understand Hormonal Mechanisms of Non-breeding Territorial Behavior

Abstract

Aggressive behaviors occurring dissociated from the breeding season encourage the search of non-gonadal underlying regulatory mechanisms. Brain estrogen has been shown to be a key modulator of this behavior in bird and mammal species, and it remains to be understood if this is a common mechanism across vertebrates. This review focuses on the contributions of Gymnotus omarorum, the first teleost species in which estrogenic modulation of non-breeding aggression has been demonstrated. Gymnotus omarorum displays year-long aggression, which has been well characterized in the non-breeding season. In the natural habitat, territory size is independent of sex and determined by body size. During the breeding season, on the other hand, territory size no longer correlates to body size, but rather to circulating estrogens and gonadosomatic index in females, and 11-ketotestosterone in males. The hormonal mechanisms underlying non-breeding aggression have been explored in dyadic encounters in lab settings. Males and females display robust aggressive contests, whose outcome depends only on body size asymmetry. This agonistic behavior is independent of gonadal hormones and fast acting androgens. Nevertheless, it is dependent on fast acting estrogenic action, as acute aromatase blockers affect aggression engagement, intensity, and outcome. Transcriptomic profiling in the preoptic area region shows non-breeding individuals express aromatase and other steroidogenic enzyme transcripts. This teleost model reveals there is a role of brain estrogen in the control of non-breeding aggression which seems to be common among distant vertebrate species.

Patterns and Scaling of Reproductive Output in Paddlefish Polyodon spathula and Its Conservation Implications

“…Several factors may lead to isometry or hypoallometry, as opposed to hyperallometry, in particular situations, however. Large size among mature females may confer other advantages besides fecundity to individual fish, such as success in defending territories (Silva et al 2020), avoidance of predation (especially in smaller species), and positive outcomes of other intra‐ or interspecies interactions. Other factors may include the demands of uniparental care (rare in externally fertilizing species such as Paddlefish but more common in internally fertilizing species; Gross and Sargent 1985) or benefits of larger maternal size on resulting larval and juvenile growth and mortality (Beldade et al 2012).…”

Role of Habenula in Social and Reproductive Behaviors in Fish: Comparison With Mammals

“…In fish, neurochemical, neuroendocrine, neuropharmacological, and neurogenetics aspects of aggression have been well examined ( Gonçalves et al, 2017 ; de Abreu et al, 2019 ; Silva et al, 2020 ), which mainly involve the POA ( Ogawa et al, 2021 ). On the other hand, aggression is strongly associated with a wide variety of social-cognitive processes such as perception, interpretation, and decision (e.g., fight or flight) ( Fiske and Taylor, 1991 ; Allen et al, 2018 ).…”

Sex Determination and Differentiation in Teleost: Roles of Genetics, Environment, and Brain

“…In addition, both hormones, T and E2, are required for testicular and ovarian differentiation, respectively [192,193]. In addition, T and E2 have positive and negative feedback on the brain, thus regulating sexual function and behaviours [194,195].…”