Abstract
BackgroundCrustaceans of the genus Daphnia are one of the oldest model organisms in ecotoxicology, ecology and evolutionary biology. The publication of the Daphnia pulex genome has facilitated the development of genetic tools to answer long-standing questions in these research fields (Science 331: 555-561, 2011). A particular focus is laid on understanding the genetic basis of the striking ability of daphnids to change their phenotype in response to environmental stressors. Furthermore, Daphnia have recently been developed into crustacean model organisms for EvoDevo research, contributing to the ongoing attempt to resolve arthropod phylogeny. These problems require the comparative analyses of gene expression and functional data, which in turn require a standardized developmental staging system for Daphnia.ResultsHere we provide a detailed staging system of the embryonic development of Daphnia magna based on morphological landmarks. The staging system does not rely on developmental hours and is therefore suitable for functional and ecological experiments, which often cause developmental delays in affected embryos and thus shifts in time reference points. We provide a detailed description of each stage and include schematic drawings of all stages showing relevant morphological landmarks in order to facilitate the application of this staging scheme.ConclusionWe present here a staging system for Daphnia magna, which is based on morphological landmarks. The staging system can be adopted for other daphnids with minor variations since the sequence of development is highly conserved during early stages and only minor heterochronic shifts occur in late embryonic stages.
Highlights
Crustaceans of the genus Daphnia are one of the oldest model organisms in ecotoxicology, ecology and evolutionary biology
Comparative aspects of D. magna development and the staging system Here we present for the first time a staging system for Daphnia magna based on morphological landmarks (Figure 13)
Pulex, D. magna and an additional cladoceran, Dunhevedia crassa, have been published - some recently - which are based on hours of development [5,11,14,15]; these cannot be used as staging systems due to large gaps and lack of morphological landmarks
Summary
Crustaceans of the genus Daphnia are one of the oldest model organisms in ecotoxicology, ecology and evolutionary biology. The publication of the Daphnia pulex genome paves the way for investigating this impressive feature on the genetic level [2] Genetic tools, such as transgenesis and RNA interference, the easy cultivation and accessibility of the direct developing eggs make D. magna an attractive organism for evolutionary developmental studies, for example, see [7,8]. Recent comparative studies on neurogenesis in D. magna have revealed considerable changes in the interactions and functions of the genes involved compared to insects [9,10] An expansion of these studies to additional developmental processes and crustacean species is required to understand the phylogenetic relationships of insects and crustaceans and the position of Cladocera within the branchiopods
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