Influência de um predador exótico (Tilápia) na morfologia e história de vida de Daphnia

Abstract

Microcrustaceans from the Daphnia genus are usually consumed by fish. However, Daphnia may display adaptive changes in morphology and life-history when exposed to predators, determining lower rates of predation and increase of fitness. Light intensity and food concentration, as well as the presence of the predator, may cause changes in the life-history and morphology of Daphnia in different intensities and directions. In experiment 1, the effects of an exotic and widely distributed predator (tilapia) on the morphology and life-history were evaluated in three Daphnia species: D. laevis (3 clones), D. similis e D. spinulata (both 1 clone). In experiment 2, the effects of the exotic predator were evaluated under varying conditions of light and food concentration on the morphology and life-history in a single clone of D. laevis. It was predicted that, in the presence of fish kairomones: 1) age and size at primipara are reduced; 2) reproduction is increased and hastened and 3) there is an increase in the relative size of the tail spines. In addition, it was expected that the increase in food concentration and light intensity would cause more intense changes in the presence of the predator. Daphnia neonates were incubated individually in media that simulated the absence or presence of the predator, through the addition of its kairomones. In experiment 2, the same procedure was performed, but environments with and without light and also with low and high concentrations of food were simulated. The individuals were observed until the third reproduction, and the response variables were age and size at primipara, number of neonates produced, tail spine length and intrinsic rates of population increase (r). In experiment 1, the exposure of Daphnia to kairomones determined changes in the life history and in the morphology of the organisms. In general, the presence of predators resulted in: 1) an acceleration in the production of offspring and an increase in the number of neonates, 2) reduction of the body size and the age at primipara and 3) increase of tail spine and r. However, significant interactions between predators and the tested species (or clone) indicate that the intensity of these effects is not uniform for all species and clones. In experiment 2, the presence of kairomones, under distinct levels of light and food concentration, determined changes in some aspects of life history and morphology of the organisms, but some changes were different from those observed in experiment 1. Light had little effects on the reaction of Daphnia to fish kairomones. Overall, Daphnia is able to detect and react to the presence of an exotic predator (tilapia) in an adaptive way, even in the absence of co-evolution between Daphnia and these exotic predators.