- The life history of freshwater cladocerans such as Daphnia spp. is strongly aVected by their environment. Factors such as temperature, food quantity and even the presence or absence of predators inXuence growth, reproduction and morphology of individuals. Recently, it has also become clear that the quality of the food can aVect various life history traits of Daphnia. More speciWcally, the eVect of the elemental composition of algae, expressed as the C:P ratio, has been studied intensively. Daphnia species diVer in their response to diVerences in the C:P ratio of their food. Until now, it has been unclear whether these species diVerences are driven by phylogenetic constraints or by adaptation to particular environmental conditions. Here we present laboratory experiments with 12 Daphnia species from three diVerent subgenera originating from a broad range of habitats. We compared somatic growth rates and sensitivity to variation in the nutrient stoichiometry of the food with habitat parameters, taking into account the phylogenetic history of the species. No associations between Wtness and habitat parameters were detected. However, we found a trade-oV between sensitivity to P-deWcient diets and the maximum growth rate on a P-suYcient diet. In several cases, this trade-oV helps to explain the association between species distribution and habitat parameters. We observed no correlation of the sensitivity to P limitation with the phylogenetic history of the genus Daphnia. Thus, we conclude that the diVerential responses among Daphnia species to variation in P content in food were driven mainly by adaptations to their local habitats, and are not constrained by deep evolutionary patterns.
