Differences in the amino acid content of four green algae and their impact on the reproductive mode of Daphnia pulex

Abstract

The enormous success of the genus Daphnia in freshwater ecosystems is at least partially due to their cyclical parthenogenetic life cycle and their ability to produce resting eggs. Recently it has been shown that resting egg production in Daphnia can be influenced by specific dietary amino acids: at high population densities (crowding), Daphnia produce resting eggs when feeding on the green alga Scenedesmus obliquus, but produce subitaneous eggs when feeding on S. obliquus supplemented with specific amino acids, or with the amino acid rich phytoflagellate Cryptomonas sp. The present study was conducted to evaluate how differences in the availability of amino acids in edible green algae affect life history and resting egg production of Daphnia pulex. In standardized growth experiments, we raised D. pulex under crowding conditions either on Ankistrodesmus falcatus, Chlamydomonas klinobasis, Chlorella vulgaris or Scenedesmus obliquus and determined juvenile somatic growth rates, production of subitaneous and resting eggs and population growth rates in order to relate them to the amount of essential amino acids in the diet. Our results show that D. pulex produces ephippia under crowding conditions with all four green algal species offered as food. However, the specific amino acid content of the green algae seems to influence the number of ephippia, respectively the number of neonates, produced. Hence, our study suggests that the availability of algae species, even though belonging to the same taxonomic group, in Daphnia’s food can change the amino acid supply and thus potentially the reproductive mode of Daphnia in experimental and natural environments.