Environment shapes the digestive performance in a Mediterranean lizard

An efficient digestive system is of pivotal importance for survival as it governs the energy flow from the environment to organisms. Reptiles require relatively little energy, and their digestive system can readily respond to internal and external shifts. Ergo, reptiles can colonize even demanding habitats by improving digestive performance. Although many studies address lizard digestion, few examine geographical variation. Here, we examine how the digestion of a single lizard species (Stellagama stellio) differs along a latitudinal and climatic gradient, comprising mainland and insular populations. Apparent digestive efficiency (ADE, the percentage of ingested energy absorbed through the gut) for lipids, proteins and sugars was used to answer the main question: is digestive performance consistent across populations (one species, one pattern) or is it dependent on habitat features (different populations, different patterns). We expected that climate and insularity would affect ADE. Indeed, the northernmost populations, inhabiting colder, rainier, less seasonal regions, achieved the lower ADEs. Insularity, however, had no effect on digestive efficiency, indicating that insular (or mainland) habitats are not all the same and local particularities may play a role. These findings suggest that each population adjusts its physiological repertoire to the local conditions.