Diet of the Insular Lizard, Podarcis lilfordi (Günther, 1874): Complementary Morphological and Molecular Approaches

SIMPLE SUMMARY: Traditionally, the diets of lizards and other small vertebrates have been studied using invasive techniques, such as the analysis of gastric contents obtained by dissection or stomach-flushing. Nowadays, the morphological analysis of the remains contained in feces is commonly used. However, these techniques require a great deal of experience to identify prey remains, and some prey items may be left undetected in the analyses. Recently, the use of molecular techniques has made it possible to identify prey from feces, thus significantly expanding the diversity of identified prey. Despite this, the molecular analysis of diets also has limitations, since it does not allow an adequate quantification of the contribution of each prey type, and, on occasion, some prey may not leave traces of DNA detectable in the feces. For this reason, here we propose a study of the diet in which the two methods of fecal analysis are complementarily used: morphological identification and identification by means of DNA analysis. ABSTRACT: The diets of insular lizards are extremely varied, depending on the different environmental characteristics of each island population. This is particularly evident in the case of the populations of small coastal islets of the Balearic Islands, where the Balearic lizard, Podarcis lilfordi, is found. The study of trophic ecology carried out by means of traditional tools, such as morphological analysis of feces, has made it possible to detect numerous prey and nutritional elements. However, these methods are clearly insufficient, as some rare groups are not detected. It is also difficult to identify remains of marine subsidies or of foods contributed to these small islands by other predators, such as seabirds. The current study demonstrates the advantages of combining morphological diet analysis with the molecular study of individual feces samples obtained from the same populations. We obtained a greater diversity of prey groups using the combined methodologies, with each method identifying prey items that were not detected using the other method. Particularly, the study of diets at the molecular level identified plant species consumed by lizards that were, occasionally, not identified in morphological analyses. Conversely, the traditional morphological study of an equivalent number of fecal samples allowed for the identification of several prey groups that had not been detected in the molecular study. From this viewpoint, the advantages and disadvantages of each methodology are discussed.