Interações comportamentais e relações predador-presa entre Erythrinus erythrinus (Bloch & Schneider, 1801) e Rivulus micropus (Steindachner, 1863) na Amazônia Central brasileira

Abstract

Mimicry is an example of convergent evolution. Aggressive mimicry is a convergence in morphological similarity between a predator and its prey, commonly known by the metaphor of the "wolf in sheep's clothing". This kind of mimicry has been reported for several species of fish. Due to a striking morphological similarity between two sympatric species of fish, the present study assessed the hypothesis of aggressive mimicry between two species of fish, a predator (Erythrinus erythrinus) and one of its prey (Rivulus micropus), which are commonly found in small terra-firme streams and temporary nearby ponds in central Amazonia. More specifically, young E. erythrinus has caudal spot that resembles females of R. micropus. In order to conduct this investigation, I gathered data from different sampling methods: field collections, field experiments and laboratorial experiments. Field collections were conducted in the Adolpho Ducke Forest Reserve (Manaus, Amazonas). I recorded size, sex, and abundance of these two species, as well as physical and chemical characteristics of the temporary ponds where they were found. Therefore, I assessed whether the presence of E. erythrinus influences population structure and sex ratio of Rivulus micropus in the temporary ponds near streams. Field experiment was designed to evaluate the movements of R. micropus (though jumping among the nearby ponds) as a response to the presence of predators or other coespecifics (males and females). I set six artificial nearby ponds and measured the distances covered by each individual across them.Laboratorial experiments were conducted in order to verify the reactions of males and females of R. micropus to the presence of coespecifics of the same sex or opposite sex, and to an E. erythrinus predator. As expected, I detected a lower abundance of E. erythrinus in relation to R. micropus. The sex ratio of R. micropus did not differ from 1:1. I detected a difference in the distance covered by males and females of R. micropus in different conditions of co-occurrence. Males R. micropus moved significantly less in the presence of females, and significantly more in the presence of young E. erythrinus when compared to control groups (isolated males and females). In laboratory experiments I found that E. erythrinus showed no predatory preference towards males or females of R. micropus. Moreover, males showed courtship behavior towards both females of their own species and young of E. erythrinus. Thus, males of R. micropus fail in distinguishing females from its predator on the base of color and behavior of its hypothetical aggressive mimic. This set of results, along with naturalistic observations, supports the hypothesis of aggressive mimicry between E. erythrinus and R. micropus. However, despite of x the closer similarity between females and its aggressive mimic, I found no evidence that one of the sexes would suffer more from predation. Because the geographical range of E. erythrinus overlaps with several dimorphic and morphologically similar species of Rivulus, it is also likely that this mimetic relationship also occur for those species.