Efeito da maturação gonadal no padrão de preferências de fêmeas por descargas de machos coespecíficos em um Peixe Elétrico Amazônico

Abstract

The mechanism by which individuals choose among potential reproductive partners imposes sexual selection through variations in secondary sexual characters on the chosen sex. The secondary sexual characters are represented by conspicuous ornaments and often act as honest contents of the individual's quality. In weakly electric fish, intraspecific communication occurs through the electric organ discharges (EOD) and, during the reproductive period, EODs become sexually dimorphic in most genera. Higher intensity of sexual dimorphism in EODs suggests the presence of sexual selection through EOD parameters. In our study, we investigated the preference of mature females for EOD parameters produced by males. First, we investigated the sexual dimorphism of individuals between the non-reproductive and reproductive periods and, subsequently, the preference of females for EODs through non-forced preference tests and analysis of EOD parameters. For this, a two-choice aquarium was used, divided into three main zones: Neutral Zone (NZ), two Confinement Zones (CZs) and two Preference Zones (PZs). Each test was performed with a triad of individuals: one female in NZ with access to both PZs and two potentially preferred individuals confined in a CZ each. Female preference was measured by the time that females occupied each PZ, which was attributed to the individual occupying the CZs. Our preference results showed that both immature and mature females performed statistically significant choices by individuals but differed in choice frequency. While immature females generally occupied for more time one of the PZs, most of the mature females made assertive choices for one of the males (one PZ). EOD parameters revealed marked seasonality in the sexual dimorphism of EODs caused by gonadal maturation in males, and EOD patterns from mature males corresponding to female preferences. The observed spontaneous choices by females were related to the variation in EOD parameters, between two well defined patterns. The preferred pattern proved to be substantially different from the non-preferred (rejected) in eight parameters. These parameters may indicate quality attributes important in the reproductive context to females. Within those, the duration of EOD was already shown to relate to the size of the individual and the longer duration of the second phase is considered a conspicuous ornament in males used in sexual selection by females. This study was the first to characterize the EOD produced by males and females from this species, which corresponded to non-breeding and breeding periods, uncovering that females base their choice on EOD characteristics from males with well-defined patterns, even outside the breeding period, and more markedly during gonadal maturation, corroborating the role of sexual selection in the evolution of EODs in this group of electric fish.