Ana Pérez-Cembranos

The islet of Vaixell, off the west coast of Ibiza (Balearic Islands, Spain), is home to a native population of the Pityusic wall lizard, Podarcis pityusensis, with the largest body size recorded for the species. These lizards live in extreme environmental conditions on an islet with a small surface area covered by very sparse vegetation. The sex ratio is balanced, and a very high incidence of missing toes and autotomized tails is observed, indicating strong intraspecific competition involving both males and females. The body growth rate, adjusted using the Gompertz model, is intense and, apparently, juvenile lizards quickly reach relatively large body sizes. This fast body growth is probably a strategy against predation pressure from conspecifics. In P. pityusensis from Vaixell, the peak growth acceleration is prenatal and practically coincides with the moment of hatching. The diet consists mainly of aggregated prey, such as ants, with the inclusion of marine subsidies, such as halophyllous and littoral isopods, and a lower consumption of plant matter compared to other insular populations of lizards from the Balearic Islands. The lizards of Vaixell are an excellent example of the adaptive response of a lacertid lizard to the extreme conditions on the small coastal islets of the Mediterranean, with very small available areas, high population density, but a small population size, of about 50 to 100 lizards, which also reach a remarkable longevity.

A major problem in current biomechanical literature is the extent to which in silico data can be validated by in vivo data across taxonomic scales. Despite frequent incongruence between in silico and in vivo data gained from precisely the same individual, biologists and palaeontologists continue to publish in silico data of single bones intended to represent entire species. Here, we aim to bridge this gap by investigating whether jaw morphology alone can be used to validate biomechanical models on the intraspecific level in a phenotypically diverse lizard, Podarcis pityusensis. We tested this by investigating how effectively in vivo bite force measurements from eight populations of this species are predicted by biomechanical models. We used alcohol-preserved specimens from each location to generate population-average and male-average morphologies of mandibles and dentaries, from which we calculated mechanical advantage as well as strength estimates from finite element analysis. Overall, we found a general lack of population-level correlation between in vivo and in silico data; however, strength estimates from finite element analysis did follow the same bite∼size relationship as in vivo bite, suggesting that biomechanical analysis of even a single bone can produce useful bite force estimates. We encourage researchers to create in silico models with maximally complex shape data and caution that intraspecific variation is a crucial aspect of in vivo and in silico biomechanics.

Many vertebrates rely on the Earth's magnetic field for orientation, navigation and spatial positioning. This ability, known as magnetoreception, is well documented across various taxa, yet its role in lizards remains poorly understood. By exposing free‐ranging Lilford's wall lizards ( Podarcis lilfordi ) to a static magnetic field in which the magnetic north was rotated to the east, we observed significant changes in their basking alignments and movement patterns. Lizards basking in the ambient magnetic field aligned along an NNE–SSW axis, whereas those in the altered magnetic field shifted to an ESE‐WNW alignment, consistent with the imposed 90° rotation. Additionally, lizards moving within the altered field exhibited directional movements along the manipulated magnetic north–south axis, contrasting with the random movements observed in controls. These findings reinforce the role of magnetic fields in lizard orientation and movement. On Aire Island, P. lilfordi is non‐territorial, with individuals displaying large home range shifts in response to food availability; hence, our results highlight the ecological relevance of magnetic orientation in species with extensive spatial dynamics. Our results provide strong evidence that both spontaneous magnetic alignment during basking and directional orientation during movement are influenced by the magnetic field, highlighting its role in the spatial behaviour of P. lilfordi . These findings contribute to the growing understanding of magnetoreception in reptiles and its ecological relevance in Lacertidae species.

Sanitja Island, the northernmost land of the Balearic Islands, is occupied by a population of Lilford’s Wall Lizard, Podarcis lilfordi, under extreme environmental conditions. It is an islet of less than 10 hectares, with low plant diversity and a complete absence of shrubs. During long-term monitoring, we studied lizard abundance over a period of approximately 40 years. Throughout several years, a group of domestic goats were introduced into the islet, leading to a collapse of the lizard population, with important collateral effects on their trophic ecology. On Sanitja Island, we observed the only case of a population of P. lilfordi in which the trend of the time series of abundance was significantly negative. The analysis of the time series indicated a lack of effect of the abiotic factors. The only factor that had a detectable effect on the population was the presence of goats. The introduction of goats caused the impoverishment of trophic resources for lizards and the change to a more diverse diet, with significantly lower consumption of plant matter. The removal of goats resulted in a partial recovery of lizard density, the recovery of a more specialized diet and the restoration of foraging behaviour on the dominant vascular plant, the sea fennel Crithmum maritimum. This foraging behaviour allows the pollination syndrome between the sea fennel and P. lilfordi. This study shows the dramatic effect of the introduction of an herbivorous competitor in an insular lizard population.

Es Colomer Island is occupied by a melanistic population of the Lilford’s Wall lizard, Podarcis lilfordi. Adult males are larger than females, with longer tails, and higher values of body mass, pileus length, head heigh, head width, hindleg length and number of dorsal scales. Adult sex ratio is balanced or slightly skewed towards males. At the summit of the islet, body condition was found to be significantly better than in almost vertical slopes. We found a higher proportion of digit amputations in adult males, probably due to frequent male–male interactions, promoted by high lizard density. During a 2024 survey, we recorded the highest known density of the Lilford’s Wall lizard. The prevalence of mites and blood parasites was 100%. The frequent intraspecific interactions, shown by the proportion of males with digit amputations, could be the source of the higher prevalence and susceptibility to blood parasite infections. The diet of lizards from Colomer is omnivorous, including several prey groups, as well as carcass remains from birds and mammals, and even conspecifics. Lizards from Colomer are an excellent example of the effects of extreme environmental conditions, with high population densities, strong intraspecific competition, the widespread presence of external and blood parasites, the extensive use of the scarce resources, and the opportunistic use of unpredictable resources in masting years, such as the fruits of the joint pine.

Urbanization and anthropic influences can drastically modify a natural habitat and transform it into an easily recognizable “urban habitat”. Human activities can also induce less severe modifications of what apparently might still look like natural habitats. Therefore, these subtle alterations may be hidden but can still cause important negative effects on plant and animals. In contrast, some species seem able to take advantage of these anthropic alterations. Here, we examined the possible effects of the anthropogenic disturbance of an apparent natural habitat on the feeding ecology and body condition of Moorish geckos, Tarentola mauritanica. For this, we compared microhabitat structure, invertebrate availability, the diet composition (estimated from fecal contents), diet selection patterns and body condition of the two populations of geckos inhabiting two contiguous small islands. These islands have similar environmental characteristics, but highly contrasting differences in urbanization and anthropogenic influence. We found that, although the abundance of potential invertebrate prey was similar on both habitats, the diversity of invertebrate prey was lower in the altered habitat. As a consequence, although composition of the diet of geckos was similar on both islands, the diversity of prey and food niche breadth were lower in the altered habitat, and patterns of diet selection changed. However, these inter-habitat differences did not seem to affect the body size and body condition of geckos. We discuss how flexibility in feeding ecology may allow some species to cope with small anthropic disturbances of the habitat.

During the last 24 years, the mutualistic interaction between the dead horse arum, Helicodiceros muscivorus, and the Balearic lizard, Podarcis lilfordi, was studied on Aire Island (Balearic Islands, Spain). From a small population of a hundred plants, the dead horse arum expanded extraordinarily throughout the island, reaching the highest known densities of the species and occupying areas of the island where it was not previously present. The current abundance of plants is a direct effect of the frugivorous activity of the Balearic lizard, which is the main, if not the only, effective seed disperser of the plant on Aire Island. However, abiotic factors predominated over biotic factors in driving abundance of plants. Over the years, plant densities varied significantly depending on the aridity of the island, with higher densities recorded in drier years. Lizards’ frugivorous activity and dispersal intensity was inversely correlated with annual rainfall. We found higher dispersal intensity in years with lower rainfall. We propose that the years of lower rainfall are those in which there is a lower prey availability. In such years, lizards compensate the shortage of other trophic resources with a more intense consumption of dead horse arum fruits. The mutualistic interaction is therefore asymmetric, since there is a greater influence of the frugivorous activity of the lizards on the plants than of the plants on lizards. It is, in short, a system chronically out of balance.

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.

Dietary studies are essential to unravel the functioning of ecosystems and ultimately to understand biodiversity. This task, which at first may seem simple, becomes especially complex in those cases of omnivorous species with highly variable diets. In this regard, the emergence of next-generation DNA sequencing methodologies represents a powerful tool to address the problem. Here we implement a high-throughput metabarcoding strategy based on the analysis of four molecular markers aimed at sequencing both mitochondrial (animal prey) and chloroplast (diet plants) genome fragments from fecal samples of two lizard species endemic to the Balearic Archipelago (Podarcis lilfordi and P. pityusensis) obtained through non-invasive methods. The results allowed for the characterization of their diets with a high degree of taxonomic detail and have contributed a large number of new trophic records. The reported diets are based mainly on the consumption of arthropods, mollusks and plants from a diversity of taxonomic orders, as well as carrion and marine subsidies. Our analyses also reveal inter- and intra-specific differences both in terms of seasonality and geographical distribution of the sampled lizard populations. These molecular findings provide new insights into the trophic interactions of these threatened endemic lizards in their unique and isolated ecosystems.

The Columbretes archipelago consists of a group of small volcanic islets located in the western Mediterranean near the east of the Iberian Peninsula. Four of its islands are inhabited by the wall lizard Podarcis liolepis, whose populations have been considered vulnerable. The purpose of this study was to assess the level of genetic diversity across the archipelago and the possible evolutionary origin of the Columbretes lizard populations. Additionally, we investigated the evolutionary ecology of these populations using a DNA-based metabarcoding approach to characterise both their microbiota and trophic interactions. The genetic results reported very low genetic diversity and corroborated the conspecificity between insular populations and P. liolepis from the mainland (Peñagolosa region). The results of the metabarcoding analyses based on faecal samples were in accordance with an omnivorous ecology, suggesting that specific microbiota communities in the insular populations might be correlated with differences in host ecology and phylogeny. These results are a valuable contribution to the current understanding of the evolution of Columbretes’ lizards and provide important information for conservation management.