Phenotypic plasticity in three Daphnia genotypes in response to predator kairomone: evidence for an involvement of chitin deacetylases

Abstract

The genetic background of inducible morphological defences in Daphnia is still largely unknown. Dissolved infochemicals from the aquatic larvae of the phantom midge Chaoborus induce so called ‘neck-teeth’ in the first three postembryonic stages of Daphnia pulex. This defence has become a textbook example for inducible defences. In a target gene approach, by applying a gradient of three Daphnia genotypes which differed significantly in neck-teeth induction in response to equal amounts of kairomone, we report a high correlation of neck-teeth induction in D. pulex and relative gene expression of two chitin deacetylases. Further, previous studies suggested genes from both the juvenoid and the insulin hormone signalling pathways as well as several morphogenetic genes downstream to be responsible for the neck-teeth induction in D. pulex. However, these data on previously suggested genes reported were not supported by this study. None of the three D. pulex clones did show an upregulation of these previously proposed candidate genes tested in this study as a response to predator kairomone, which is interpreted as the result of refined methods used for both RNA sampling and kairomone enrichment, which yielded unambiguous results compared to earlier studies. The assessment of a clonal gradient of Daphnia in the presence and absence of infochemicals provides a promising approach to identify further genes being involved in the induction of morphological defences by correlating gene expression and morphology.