Testing the hypothesis of loss of defences on islands across a wide latitudinal gradient of Periploca laevigata populations

PREMISE OF THE STUDY: We tested a hypothesis that predicts loss of chemical defences on island plant populations (LCDIH) as an evolutionary response to limited herbivore pressures. METHODS: Using a common garden approach, we grew 16 populations (N = 286 seedlings) of Periploca laevigata, a Mediterranean shrub for which previous studies suggested tannin-mediated responses to animal browsing. Our experimental setting represented a wide latitudinal gradient (37-15ºN) encompassing three island systems, virtually free of large herbivores, and three mainland areas. Putative chemical defences were estimated from tannin-protein precipitation assays, and inducible responses in growth and chemical traits were assessed between seasons and by subjecting plants to a pruning treatment. KEY RESULTS: We failed to find support for the LCDIH, since island populations (Canary Islands, Cape Verde) displayed increasingly higher constitutive levels of tannins at lower latitudes. Seasonality, but not experime...