Offspring size in Daphnia: does it pay to be overweight?

Variation in offspring size and number has been described for a wide range of organisms. In this study I investigated the relationship between resource level of the mother and size of her offspring in the cladoceran Daphnia magna, in order to assess whether offspring produced at different food levels are optimal in size for these food levels. Optimal offspring size was defined as the size of offspring that yields the highest parental fitness (i.e. offspring of optimal size have the highest juvenile fitness per unit maternal effort invested in them). I observed that especially at the higher food levels, daphnids produced offspring that are larger than the computed optimal offspring size at these food levels. I interpret this as a mechanism to avoid starvation of neonates in the case of suddenly deteriorating food conditions.