My project (funded by the Förderinitiative Evolutionsbiologie of Volkswagen Stiftung) is about the peptide based defense system in frogs and toads (Anura). Rich in cutaneous glands, both frogs and salamanders (Caudata) produce a wide range of defensive compounds in their skin, such as alkaloids (in Dendrobatidae, Bufonidae, Mantellidae, Myobatrachidae, and Salamandridae). Moreover biologically active peptides can be found acting either neuroactive or antibiotic. Thus, the defence system in anuran amphibians bears solutions against both macro- and micropredators.
In particular, I focus on the evolution of antimicrobial peptides within Anura. Not only useful for the frog itself these molecules are also of interest for medical research. Peptides from the White's Tree Frog (Litoria caerulea) for instance potently inhibit infection of T-cells with HIV.
All genes encode a prepropeptide consisting of three structural domains: a signal peptide, an intervening acidic spacer and the physiologically active peptide domain. While the sequence of the signal peptide – and to some extent the spacer as well – is highly conserved the mature peptide is not. This hypervariable sequence yielded in an extraordinary diversity of antimicrobial peptides among Anura (ca. 600 peptides from 100 species investigated). It has been proven that this was driven by positive selection. Besides there are only few examples for peptides that occur in more than one species. Hence, conserved regions are more suitable in order to study evolutionary issues. A comparison of signal peptide sequences is helpful to identify gene families. Apparently there are at least three different gene families encoding antimicrobial peptides that can be distinguished by their distinct signal peptides. Though, each gene family can be found within a particular taxon only. That leaves the question whether or not a gene for antimicrobial peptides evolved independently multiple times in frogs and toads? Former studies were basically restricted to species from Hylidae and Ranidae. Therefor, new data from uninvestigated taxa will be gathered in this project and might help to answer this question. I apply methods of molecular biology (mRNA isolation, PCR, cloning) in order to get genetic information out of a sample of secretion.