Molecular detection of invertebrate prey in vertebrate diets: trophic ecology of Caribbean island lizards

Understanding community assembly and population dynamics frequently requires detailed knowledge of food web structure. For many consumers, obtaining precise information about diet composition has traditionally required sacrificing animals or other highly invasive procedures, generating tension between maintaining intact study populations and knowing what they eat. We developed 16S mitochondrial DNA sequencing methods to identify arthropods in the diets of generalist vertebrate predators without requiring a blocking primer. We demonstrate the utility of these methods for a common Caribbean lizard that has been intensively studied in the context of small island food webs: Anolis sagrei (a semi-arboreal trunk-ground' anole ecomorph). Novel PCR primers were identified in silico and tested in vitro. Illumina sequencing successfully characterized the arthropod component of 168 faecal DNA samples collected during three field trips spanning 12months, revealing 217 molecular operational taxonomic units (mOTUs) from at least nine arthropod orders (including Araneae, Blattodea, Coleoptera, Hemiptera, Hymenoptera, Isoptera, Lepidoptera and Orthoptera). Three mOTUs (one beetle, one cockroach and one ant) were particularly frequent, occurring in 50% of samples, but the majority of mOTUs were infrequent (180, or 83%, occurred in 5% of samples). Species accumulation curves showed that dietary richness and composition were similar between size-dimorphic sexes; however, female lizards had greater per-sample dietary richness than males. Overall diet composition (but not richness) was significantly different across seasons, and we found more pronounced interindividual variation in December than in May. These methods will be generally useful in characterizing the diets of diverse insectivorous vertebrates.