Life history strategies in Daphnia: a review and predictions

The cladoceran Daphnia is an ideal organism for the comparative study of life history strategies due to its extensive geographic range and the great deal known of its biology. Biotic selection pressures on components of life history strategies include predation, food, and competition. Abiotic pressures include temperature, photoperiod, and environmental chemistry. In addition, it can be demonstrated that stochastic life history theory, based on the differential survivorship of juveniles and adults, is also an important component in the evolution of Daphnia life histories. As an example of the interaction of these pressures two Daphnia species and their life histories are compared. Daphnia pulex has a very broad geographic range extending through most temperate areas of North America, and has a correspondingly broad array of life history characteristics but may be characterized as maturing rapidly and reproducing with many large broods of small neonates. In comparison, D. middendorffiana, an arctic species, requires more time to mature and produces many fewer broods of large.neonates.