An important new tool is the development and use of Daphnia-specific DNA microarrays, which are now being tested for their applicability to ecological studies. Using microarrays, RNA populations representing all expressed genes can be hybridized to a complete set of genomic probes, typically represented as microscopic dots of individual DNAs printed on glass slides. Statistical analyses of the full dataset can reveal networks of genes that are expressed in a coordinated fashion, while the expression pattern differences associated with various treatments can reveal candidate genes underlying specific phenotypic changes. Such information is critical to developing a mechanistic understanding of the extent to which species can cope with environmental change, both in terms of short-term phenotypic plasticity and long-term evolutionary adaptation. Daphnia microarrays are produced at the CGB by printing cDNA obtained from our EST sequencing projects.