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

Abstract

29The expression of territorial behavior in wild species is especially suited to explore how 30 animals integrate individual traits with dynamic environmental and social contexts. In this 31 study, we focused on the seasonal variation of the determinants of territory size in the weakly 32 electric fish Gymnotus omarorum. This species is a seasonal breeder that displays year-33 long territorial aggression, in which female and male dyads exhibit indistinguishable non-34 breeding territorial agonistic behavior and the only significant predictor of contest outcome 35 is body size. We carried out field surveys across seasons that included the identification of 36 individual location, measurements of water physico-chemical variables, characterization of 37 individual morphometric and physiological traits, and their correlation to spatial distribution. 38Although Gymnotus omarorum tolerates a wide range of dissolved oxygen concentration, 39 territory size correlated with dissolved oxygen in both seasons. In the non-breeding season, 40we show that territory size is sexually monomorphic and explained only by body size. In the 41 breeding season, while body size no longer correlated with territory size, evidence of sexual 42 differences in territory size determinants emerged. First, the overall spatial arrangement 43 adopted a sexual bias. Second, territory size depended on gonadal hormones in both sexes, 44which was expected for males, but not previously reported in females. Third, females' 45 territory size correlated with gonadal size and females showed relatively larger territories 46 than males, probably to meet sexually dimorphic energetic requirements. This study 47 provides evidence of seasonal changes in factors correlated with territory size and 48 contributes to the understanding of the mechanisms underlying behavioral plasticity. 49 50 Keywords 51 Non-breeding aggression, sexual dimorphism, Gymnotus omarorum, gonadal steroids 3 52 53

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

“…This data falls in line with the well documented relationship between androgens and male territorial behavior ( 60 – 62 ). In contrast, both female GSI and circulating estradiol show high predicting power on territory size, which constitutes the first report to associate circulating estradiol and territory size in a vertebrate species ( 59 ). In the light of the evidence that estradiol promotes female aggression ( 63 – 65 ), ovarian estradiol is likely involved in the modulation of breeding territorial aggression in this species.…”

“…This interesting difference is probably due to sex-biased reproductive requirements associated to anisogamy, which may lead to higher metabolic requirements in females and thus the need for larger foraging grounds. In male G. omarorum gonadosomatic index (GSI) did not show correlation to territory sizes, but circulating 11-ketotestosterone (11-KT, the main bioactive androgen in teleost fish) marginally predicted territory size ( 59 ). This data falls in line with the well documented relationship between androgens and male territorial behavior ( 60 – 62 ).…”

“…During the breeding season (corresponding to the austral spring-summer, from December to February), this sexually monomorphic species displays similar patterns of spatial arrangement for males and females ( 59 ). In resting diurnal conditions, both males and females are found occupying individual spots, distanced at least a meter away from their closest neighbor.…”

“…Sex of individuals does not bias spacing, as closest neighbors are randomly opposite-sex or same-sex. Body size, but not sex, correlates positively with territory size ( 59 ). Motivation to maintain territories in the non-breeding season may be related to the fact that these fish continuously produce electric signals as a means of communicating and imaging their world.…”

Spooky Interaction at a Distance in Cave and Surface Dwelling Electric Fishes

“…Territoriality may occur as a result of uneven distribution of food resources in the cave, due to other physical features that impact the fish, or a consequence of plesiomorphic social and/or reproductive behaviors. Territoriality has been described in other genera, such as Gymnotus (Zubizarreta et al, 2020).…”