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Abstract: The zooplankter Daphnia exilis was found recently in reservoirs of central Chile. This species has been described as being tolerant to osmotic stress and chemical pollution, although the available information about its ecological properties is limited. Motivated by likelihood of being witnesses to a biological invasion, in this study we contribute to expand the knowledge of this exotic species through evaluating its ability to respond phenotypically to two major ecological factors: predation risk and food availability. Specifically, we analysed shifts in life-history and morphological traits of D. exilis in response to fish-released infochemicals, at different food densities. Our results revealed that the organisms were affected in their temporal trajectories of body size and shape, as well as in maturation time and fertility, in response to both predator cues and food availability. The presence of fish kairomones led to a decrease of age at maturity, and an increase of reproduction size and fecundity, especially at lower levels of resources. Our analyses indicated that asymptotic body size was affected only by food level, but the rate of increase in body size was sensitive to both fish kairomones and food level. The relative length of the tail spine decreased during early ontogenetic states, reaching a minimum around the age at maturity. This pattern was significantly enhanced in the presence of fish kairomones. However, our results did not match completely the typical responses of daphnids to fish kairomones. [Copyright &y& Elsevier]

1. Here, we report morphological and life-historical changes in the cladoceran Daphnia ambigua in response to chemical cues released by the predatory water mite Piona chilensis. Both species are common inhabitants of southern temperate lakes. 2. We found significant differences in adult body size at first, second and third reproduction. Also, individuals exposed to kairomones had longer tail spines at first reproduction, and the resultant offspring had smaller bodies and shorter tail spines. 3. Exposure to mite cues did not exert effects on brood size at first reproduction, but decreased offspring number in subsequent broods. Similarly, only the second and third reproduction events were delayed by kairomone exposure. 4. The intrinsic population growth rate of predator-induced animals was lower than that in controls, but simulations based on a parameterized matrix model showed that the fitness costs could be overcome if the reported phenotypic responses reduced predation rate moderately. The gain in protection from predators needed to cancel out the reduction in fitness associated with predator cues was directly related to juvenile survival and fertility, and inversely related to adult survival. 5. This is the first work reporting phenotypic plasticity in Cladocera in response to kairomones released by water mites, which are conspicuous predators in many austral fresh waters. [ABSTRACT FROM AUTHOR]

Studies of life history aim to explain patterns in the evolution of reproductive investment, growth, and survival. Trade-offs between traits are a fundamental component of life history theory. In herbivorous arthropods life history traits are often responsive to variation in numerous environmental factors, especially diet quality. Using three artificial diets under controlled laboratory conditions, we examined changes in life history traits (i.e. growth rate, offspring number, offspring size, incubation period), trade-offs between traits, and maternal effect on the growth rate of offspring, in the common woodlouse (terrestrial isopod), Porcellio laevis. The high protein diet had significant impacts on offspring production, triggering a smaller-sized offspring, and demonstrating a trade-off between these last two traits. The high carbohydrate diet seldom exerted a significant effect on incubation period. The quality of dietary items evidently has important consequences on the life history of the mother and, thus, on offspring growth; the directions of these effects, however, were opposite. Mothers fed diets with high protein concentrations presented significant maternal effects, measured as offspring growth rate during later ontogeny. Our results support the notion that protein, rather than carbohydrate, concentrations in the diet limit herbivorous arthropods, and have significant consequences on life history traits, as was seen for P. laevis. Clearly, the change in phenotypic correlations between incubation period and offspring number from negative to positive is an empirical demonstration of the context dependence of life history trait trade-offs. [ABSTRACT FROM AUTHOR]