Most studies on amphibian skin peptides have an explicit pharmacological focus, and the origin, diversity, and functional diversification of these molecules therefore remain poorly understood. Antimicrobial peptide research in amphibians has been restricted to relatively few closely related genera in a limited number of families. Furthermore, although behavioral tests indicate chemical communication during courtship in many amphibian species, only a single pheromone peptide has been characterized in anurans (frogs and toads), and only two in caudates (salamanders and newts). We propose an integration of transcriptome analyses, peptidome analyses, functional assays, and phylogenetic analyses to: 1. Identify and characterize novel antimicrobial and pheromone skin peptides in a representative of all amphibian families. 2. Study the evolution of these molecules by mapping diversity and function on well-supported phylogenies. 3. Determine the relative contribution of different genetic mechanisms to the rise of antimicrobial and pheromone peptide diversity (e.g. recruitment from genes with other functions, tandem duplications, gene conversion, ...). 4. Test the relative contributions of skin peptide evolution (ecological adaptation and/or sexual signal differentiation) in shaping species diversity in amphibian evolutionary radiations. The results of this project are expected to throw a new light on amphibian defense and chemical communication. Since (1) there is a correlation between resistance to lethal infection and synthesis of antimicrobial peptides by the host amphibian, and (2) because systems of chemical communication are especially vulnerable to disruption by anthropogenic change, this project is expected to form an important contribution in the struggle against amphibian decline.