Revealing proximate causes of dwarfism of the natterjack toad (Epidalea calamita) in southern Spain

Climatic data was obtained from Worldclim Version 1&2, soil data from the European Soil Database, and Normalized Difference Vegetation Indices (NDVI) from satellite images through the Modis Vegetation index MOD13Q1. For skeletochronology, telomere, and microsatellite analyses we collected a total of 180 Epidalea calamita adult males across all populations. We then clipped the fourth toe of the right hindlimb that we then used for cross sectioning and DNA extractions. Stable isotope data were obtained from E. calamita egg clutches, which allows direct assessment of the diet of the female without harming any adults. We collected small sections of egg clutches that were kept under identical conditions in the lab until hatching and then determined the carbon and nitrogen levels of these samples. Standard metabolic rate was assessed in a terrestrial respirometer overnight, for which we brought in mature males from the field at night. Advertisement calls were recorded using a shotgun microphone and subsequently analysed using the software Raven Pro v.1.4. For female behavioural assays we brought in receptive females at night to the lab and played back recorded calls. All individuals were released at dawn and no individual was harmed.