Resurrected Ceriodaphnia quadrangula highlight differences between pheno- and genotypic expressions

The hatching of cladoceran ephippia from a 15-cm long sediment core was investigated, and Ceriodaphnia quadrangula clones were isolated from different sediment layers. Bosmina microfossil data were also analyzed, and compared with the corresponding data from a Pb210 dated core, which allowed us to infer the age of the sediment layers. Using changes in Bosmina microfossil morphologies, we were, furthermore, able to infer the presence of different regimes of fish predation. C. quadrangula was found to hatch in layers with an inferred age of approximately a century. Newly hatched individuals had smaller eye-size in sediment layers corresponding to high predation by young-of-the-year perch. Newly hatched individuals also generally had a marked neck-spine. In contrast, morphological characters of C. quadrangula clones reared in the laboratory over several generations showed no variation in relation to predation regime, indicating the absence of fixed genotype level changes. Furthermore, the laboratory grown clones only rarely produced a neck-spine. The results suggest phenotypic variation in response to the regime under which ephippia were produced.