Status of the largest extant population of the critically endangered Aeolian lizard Podarcis raffonei (Capo Grosso, Vulcano island)

Abstract

The Aeolian wall lizard Podarcis raffonei is an island endemic that survives only on three tiny islets, and on the Capo Grosso peninsula of the Vulcano island, thus is among the European vertebrates with the smallest range and one of the most threatened by extinction. This species is declining due to competition and hybridization with the non-native lizard Podarcis siculus, but a regular monitoring program is lacking. Here we assessed the size and status of the Capo Grosso population of P. raffonei on Vulcano. In September 2015 we captured 30 individuals showing the typical brown phenotype of P. raffonei, while one single male showed a green phenotype, apparently intermediate between P. raffonei and the non-native Podarcis siculus. In May 2017, only 47% of 131 individuals showed the typical brown phenotype (P. raffonei-like) and 53% showed the green phenotype (P. siculus-like). Based on N-mixture models and removal sampling the estimated size of the Capo Grosso population was of 800–1300 individuals in 2017, being similar to 2015; available data suggest that the total range of the species could be as small as 2 ha. The frequency of individuals with the typical P. raffonei phenotype dramatically dropped between two samplings with a parallel increase of individuals displaying the green phenotype. Observation on outdoor captive-bred individuals demonstrates plasticity for colouration in P. raffonei individuals from Capo Grosso, with several individuals showing the typical brown pattern in September 2017 and a green pattern in March 2021. Non-exclusive hypotheses, including hybridization with P. siculus and plasticity in colour pattern of P. raffonei, are discussed to explain the phenotypic shifts of the P. raffonei population of Capo Grosso. While genomic evidence is required to reach conclusions and investigate eventual hybridization, it is urgent to undertake a programme for the monitoring and management of this lizard.

Reconstructing the complex colonisation histories of lizards across Mediterranean archipelagos

“…For instance, the Aeolian archipelago hosts the Critically Endangered, endemic lizard Podarcis raffonei. The decline of this species is often explained by the recent introduction of P. siculus (Capula, 2002;Ficetola et al, 2021), but our reconstruction of colonisation history suggests a more complex pattern with both natural and human-aided colonisation events. Only in some islands it is likely that P. siculus has been introduced recently by human activities (e.g.…”

“…ddRAD sequencing, Demographic history, Island biogeography, Overseas dispersal, Podarcis siculus, Vicariance, wall lizards Senczuk et al, 2018). Yet in other nearby archipelagos, the species has most likely been introduced by humans and may therefore represent a threat to island endemics (Capula, 2002;Ficetola et al, 2021).…”

“…In some of these islands, the lizard is presumably native, with ancient endemic lineages (Podnar et al, 2005; Senczuk et al, 2018). Yet in other nearby archipelagos, the species has most likely been introduced by humans and may therefore represent a threat to island endemics (Capula, 2002; Ficetola et al, 2021). Nevertheless, in most cases, its biogeographical status is unknown (Bonardi et al, 2022), which challenges management actions.…”

Evolutionary and biogeographical support for species-specific proteins in lizard chemical signals

“…Sympatry of closely related species may impose high cost in term of fitness to one or both species because of interspecific aggression (Tynkkynen et al, 2005), competition for resources or reproductive interactions (e.g., hybridization). Indeed, both current and past hybridization are well-known in the genus Podarcis (Capula, 1993(Capula, , 2002Pinho et al, 2009;Ficetola et al, 2021) and genetic evidence of reticulation suggests that its effectiveness is not 100% (Pinho et al, 2009;Caeiro-Dias et al, 2021;Yang et al, 2021). Consequently, selective pressures are expected to promote divergence in species traits involved in species recognition, to reduce detrimental interactions, but only where they occur in sympatry.…”

Does hybridisation with an invasive species threaten Europe’s most endangered reptile? Genomic assessment of Aeolian lizards on Vulcano island

“…In a survey of 131 lizards in 2017, a large number (>50%) of individuals from Capo Grosso showed an intermediate phenotype, with green patterns and dark markings on the throat (Figure 2). This was suspected to indicate extensive hybridisation (Ficetola et al, 2021); however, individuals kept in captive-breeding programs showed strong plasticity in colour pattern with a seasonal shift towards a green phenotype (Ficetola et al, 2021). Thus, the true hybrid status of the Capo Grosso population of P. raffonei remains unknown.…”