Paving the way for a Conservation Project: characterization, demography and ecology of Podarcis raffonei and the other lizards of the Aeolian Archipelago

Amidst a global decline in reptile species and populations, the Aeolian wall lizard exemplifies this trend. Podarcis raffonei, one of Europe’s most threatened vertebrates and listed as Critically Endangered on the IUCN Red List, faces severe risks due to its restricted, fragmented range, low genetic variability, and pressures from invasive P. siculus that contributed to the current relict distribution. This species is currently distributed on three small rocks (La Canna, Scoglio Faraglione, Strombolicchio) and a promontory on the island of Vulcano (Capo Grosso). Despite EU Habitat Directive obligations, regular population monitoring has not been conducted, leaving the conservation status of most populations missing or outdated. This thesis aims to gather essential information on both the autochthonous and invasive lizards to inform a comprehensive conservation strategy for P. raffonei. In the first chapter, I studied the color variation across seasons and years of the Aeolian lizard population on the Capo Grosso promontory. In 2017, a very high proportion (around 90%) of lizards with green coloration was observed in nature. This coloration was interpreted as an intermediate phenotype between P. raffonei and P. siculus, suggesting a potential near extinction status for this population due to hybridisation. To assess if color variation is determined by hybridisation or natural variation over time, I carried out a quantitative analysis of dorsal color in captive and natural populations. I demonstrated that P. raffonei, like other conspecifics, exhibits seasonal variation. In spring, males consistently display a more yellow-green hue compared to females. Between-year analyses, including field data, show that seasonal variation in the three components of color (hue, brightness, and saturation) analyzed in this study differed across years. These findings, together with the genetic analyses on the captive lizards, confirm that green dorsal coloration on Vulcano Island is a natural trait of P. raffonei and should not be used as a distinctive characteristic of P. siculus or hybrids on Capo Grosso. The second chapter focuses on identifying optimal monitoring methods for P. raffonei populations and updating population estimates for Capo Grosso and Scoglio Faraglione. Capture-Mark-Recapture (CMR) models, for both closed and open populations, and N-mixture models were applied on data collected from spring 2022 to October 2023. Maximum lizard detectability occurred in spring, but daily patterns differed between sites. Although Bayesian N-mixture models performed well, the demographic information at individual level provided by CMR justifies the greater effort required for this method. Significant differences in demographic trends, body condition, and sex ratio between the two populations highlight the urgent need for conservation action for P. raffonei at Capo Grosso, where population estimates have sharply declined since 2017, in contrast to stable estimates at Scoglio Faraglione since 2006. In the third chapter, I explored the potential effects of recent overwinter goat pasture abandonment at Capo Grosso and the interaction with black rats (Rattus rattus) on P. raffonei decline. The interruption of grazing activity generated a sudden increase in the density of adventitious vegetation (mainly Rubus sp.), leading to a reduction in the suitable habitat for P. raffonei and an increase for the rat's elective habitat, whose density increased significantly. Using DNA metabarcoding of lizard and rat fecal pellets, I investigated possible interspecific interactions. No lizard DNA was detected in rat feces, and dietary overlap between rats and lizards was significant but limited to the vegetation component of the diet. DNA metabarcoding proved valuable for studying lizard diet, especially the plant component, which has been underestimated in previous research on trophism of P. raffonei. Further analyses on a wider sample of both fecal pellets and rat stomach content, in different seasons, will help clarify the role of invasive black rats on P. raffonei decline. In the fourth chapter, I examined color variation in Podarcis siculus across the Aeolian islands, revealing that environmental conditions had a modest influence on dorsal color patterns, with low explanatory power for saturation and the extent of red and orange coloration. Black coloration displayed a distinct pattern, increasing with male body size but remaining constant in females, and was less prominent in warmer sites. Within the Panarea sub-archipelago, populations on Lisca Bianca, Bottaro, Basiluzzo, and Panarea clustered together in the red-orange-yellow gradient, setting them apart from the other western Aeolian islands. These findings suggest that, although there is evident color variation among populations, it likely reflects factors related to the specific historical or ecological context of each island rather than the local-scale factors investigated in this study. The fifth chapter explores the drivers of sexual dimorphism (SD) in P. siculus across the Aeolian archipelago, focusing on body size and head shape in relation to environmental resource availability. Significant geographic variation in SD was observed, with body condition and ecosystem productivity emerging as primary predictors. These results suggest that SD in P. siculus is both condition- and context-dependent, reinforcing that environmental factors play a substantial role in shaping intraspecific variability in this species. In the final chapter I critically examined the use of subspecies as conservation targets by assessing the evolutionary and phenotypic distinctiveness of Italian wall lizard subspecies in the Aeolian Archipelago. A comprehensive morphological and genetic analysis reveals that none of the Aeolian subspecies represents a distinct evolutionary lineage, indicating that the observed phenotypic variation likely reflects a recent origin. Expanding this analysis to seven Podarcis species in Italy, results show that only a small fraction (< 9%) of subspecies align with true evolutionary units. This study highlights that intraspecific taxonomy alone is an unreliable basis for defining conservation priorities. A more effective approach would integrate genomic and phenotypic data to identify conservation units of true evolutionary significance. In conclusion, the data obtained in this thesis underscore an urgent need for targeted conservation measures to safeguard Podarcis raffonei. The Capo Grosso population is experiencing severe demographic decline and faces novel, unanticipated threats. This decline, likely driven by recent land-use changes, requires immediate mitigation strategies to support in situ population persistence. Additionally, establishing a backup population through captive breeding and reintroduction programs is essential for long-term survival. The need for suitable sites to accommodate P. raffonei populations necessitates the translocation of P. siculus from the small islets of the Panarea microarchipelago to Panarea itself, a move supported by the genetic analyses presented in this thesis. While P. siculus populations in the Aeolian Islands exhibit notable phenotypic variability, conservation priorities must focus on preserving P. raffonei, requiring strategic compromises to prevent the extinction of this endemic species.