Potentials and limitations of adaptive plasticity in filtering screen morphology of Daphnia (Crustacea: Cladocera)

Abstract

Mechanisms of the phenotypic plasticity of morphological parameters of the filtering screens were studied in Daphnia galeata. The results of the laboratory experiments showed that the filtering setae number (FSN) once fixed in the new born individuals remained constant up to the first adult instar (end of the experiment). Concurrently, in addition to genetic diversity, strong phenotypic plasticity and the close correlation with size at birth result in a broad variation range of the FSN when populations from various conditions are examined. Despite the broad variation range, the mean FSN in the D. galeata x cucullata hybrid and parental species was found to be a taxon-specific trait. The filtering setae length is the parameter that predominantly determines the filtering screen area (FScrA); it is relatively uniform in neonates and exhibits strong food-dependent plasticity during ontogenesis. The correlation of the FSN and the FScrA is weaker but still significant. Therefore the upper limit of FScrA is lower in screens with low FSN. There is a negative correlation between the intersetal gap size and the FSN. The results of this study present mechanisms of filtering screen plasticity that have a broader relevance for species of the genus Daphnia.