DNA metabarcoding diet study of Teira dugesii

Living on islands entails numerous challenges for animals, among which resource scarcity stands out. To overcome this condition, many lizards can supplement their insectivorous diet with increasing portions of plant material. The Madeira wall lizard Teira dugesii is a medium-sized lacertid lizard, endemic to the Madeira and Selvagens archipelagos. Like many other lizards, adults are sexually dimorphic with males being bigger than females. Previous dietary studies on morphological scatology of T. dugesii identified a higher proportion of plant over animal prey items, changing according to the location and sex of the individuals. Here, we used DNA metabarcoding to study the diet of this lizard species, a technique known to provide a better taxonomical resolution and able to detect soft-body prey items that often go undetected in morphology-based studies. We detected 289 prey items belonging to eight classes of animals and three classes of plants, encompassing 58 distinct orders and 140 families. 63 of these prey items were identified up to the species level. The results support a strong trend towards herbivory with plants representing almost 74% of the prey occurrences in contrast to the 26% of animal prey. However, herbivory does not seem to change with locality, but instead with size and mass in males. As males grow bigger and heavier, they significantly increase their plant matter intake. This occurs because larger bodies and abdomens allow for the allocation of a longer and more complex digestive system able to better decompose cellulose. Additionally, heavier animals (likely males) are feeding on a richer diet regime. On the other hand, diet richness and composition were not affected by neither sex nor size, while the locality had a significant effect on both diet components likely mirroring the distinct faunistic and floristic characteristics of these areas.