Interaction of changes in food quality and temperature reveals maternal effects on fitness parameters of a keystone aquatic herbivore

Abstract

We investigated the interaction of intergenerational temperature and food quality change on the fitness of two species of Daphnia, a freshwater keystone herbivore. The effect of a change in temperature (15°C vs. 20°C) and food quality (Cryptomonas sp. as high‐quality food vs. Chlamydomonas sp. as relatively low‐quality food) on juvenile growth rate and clutch size of Daphnia magna and Daphnia pulex was measured in 16 combinations of maternal and offspring environments in standardized growth assays. Both species showed similar responses. The positive effect of food quality on growth rate and clutch size was stronger if the maternal diet was of low quality. High maternal diet quality generally increased growth rate and reproduction, especially if the offspring diet was of low quality. The maximum fitness was attained by animals acclimated at 15°C and growing at 20°C, combining the faster growth rate at warm assay temperature and bigger clutch size of cold‐acclimated animals. Intergenerational temperature regime had a strong influence on the effects of maternal and offspring food quality. Good maternal food quality was more important for fitness under less favorable temperature conditions. Low offspring food quality was more detrimental to fitness in animals experiencing temperature change between maternal acclimation and growth assay and less so under constant temperature conditions. Intergenerational changes in temperature and the maternal effects of food quality strongly affect the dietary requirements of these organisms. Hence, extrapolation from studies conducted under constant temperature conditions may seriously underestimate dietary constraints in natural environments.