PLOS ONE RESEARCH ARTICLE Status of the largest extant population of the critically endangered Aeolian lizard Podarcis raffonei (Capo Grosso, Vulcano island) Gentile Francesco Ficetola1,2, Iolanda Silva-Rocha3, Miguel A. Carretero3,4, 5 6 7 8 9 Leonardo Vignoli , Roberto Sacchi , Andrea Melotto , Stefano Scali , Daniele SalviID * 1 Department of Environmental Science and Policy, Università degli Studi di Milano, Milano, Italy, 2 CNRS, Laboratoire d'Ecologie Alpine (LECA), Univ. Grenoble Alpes, Grenoble, France, 3 CIBIO, Centro de InvestigacËão em Biodiversidade e Recursos GeneÂticos, Universidade do Porto, InBio LaboratoÂrio Associado, Vairão, Portugal, 4 Departamento de Biologia, Faculdade de Ciências da Universidade do Porto, Porto, a1111111111 Portugal, 5 Dipartimento di Scienze, Università Roma Tre, Rome, Italy, 6 Department of Earth and a1111111111 Environmental Sciences, University of Pavia, Pavia, Italy, 7 Centre of Excellence for Invasion Biology, a1111111111 Department of Botany and Zoology, Stellenbosch University, Stellenbosch, Western Cape, South Africa, a1111111111 8 Museo di Storia Naturale di Milano, Milano, Italy, 9 Department of Health, Life and Environmental a1111111111 Sciences, University of L'Aquila, Via Vetoio, L'Aquila, Italy * [email protected] OPEN ACCESS Abstract Citation: Ficetola GF, Silva-Rocha I, Carretero MA, The Aeolian wall lizard Podarcis raffonei is an island endemic that survives only on three Vignoli L, Sacchi R, Melotto A, et al. (2021) Status of the largest extant population of the critically tiny islets, and on the Capo Grosso peninsula of the Vulcano island, thus is among the Euro- endangered Aeolian lizard Podarcis raffonei (Capo pean vertebrates with the smallest range and one of the most threatened by extinction. This Grosso, Vulcano island). PLoS ONE 16(6): species is declining due to competition and hybridization with the non-native lizard Podarcis e0253631. https://doi.org/10.1371/journal. siculus, but a regular monitoring program is lacking. Here we assessed the size and status pone.0253631 of the Capo Grosso population of P. raffonei on Vulcano. In September 2015 we captured Editor: Ulrich Joger, State Museum of Natural 30 individuals showing the typical brown phenotype of P. raffonei, while one single male History, GERMANY showed a green phenotype, apparently intermediate between P. raffonei and the non-native Received: March 8, 2021 Podarcis siculus. In May 2017, only 47% of 131 individuals showed the typical brown pheno- Accepted: June 10, 2021 type (P. raffonei-like) and 53% showed the green phenotype (P. siculus-like). Based on N- Published: June 23, 2021 mixture models and removal sampling the estimated size of the Capo Grosso population Copyright: © 2021 Ficetola et al. This is an open was of 800±1300 individuals in 2017, being similar to 2015; available data suggest that the access article distributed under the terms of the total range of the species could be as small as 2 ha. The frequency of individuals with the Creative Commons Attribution License, which typical P. raffonei phenotype dramatically dropped between two samplings with a parallel permits unrestricted use, distribution, and increase of individuals displaying the green phenotype. Observation on outdoor captive- reproduction in any medium, provided the original author and source are credited. 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 Data Availability Statement: All relevant data are within the manuscript. 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 Funding: This study was funded by the Mohamed bin Zayed Species Conservation Fund (Project shifts of the P. raffonei population of Capo Grosso. While genomic evidence is required to 162514415). MAC and ISR are supported by grant reach conclusions and investigate eventual hybridization, it is urgent to undertake a pro- 28014 02/SAICT/2017 and SFRH/BD/95745/2013 gramme for the monitoring and management of this lizard. from FCT, Portugal. The authors acknowledge support from the University of Milan through the APC initiative. PLOS ONE | https://doi.org/10.1371/journal.pone.0253631 June 23, 2021 1 / 15 PLOS ONE Status of Podarcis raffonei on Vulcano Competing interests: The authors have declared Introduction that no competing interests exist. Monitoring of populations is an essential conservation task. Frequent monitoring is necessary to determine natural fluctuations, to detect declining trends, to ascertain the conservation sta- tus of populations and species and to ensure the effectiveness of eventual management mea- sures [1±4]. This is recognised by the Habitats Directive of the European Union (Directive 92/43/EEC), which requires that member States regularly measure trends of populations of all listed species, to identify conservation priorities and to assess the efficiency of undertaken pro- tection measures. Regular monitoring is also pivotal to identify threats. For instance, factors potentially driving population changes can be detected during monitoring programs, and this can allow to deliver effective and prompt conservation solutions [5, 6]. A continuous monitor- ing of conservation status and threats is particularly important for narrow endemic species that are more likely exposed to stochastic or directional threats than taxa with occurrences dis- tributed over larger areas [7]. Monitoring programs are often limited by accessibility. Difficult access makes surveys more expensive and less feasible, thus the least accessible areas rarely are the focus of regular moni- toring, and biodiversity surveys often remain concentrated in the most accessible areas [4, 8, 9]. Therefore, species living in inaccessible, remote areas often suffer insufficient monitoring, and declines or population changes might remain unnoticed. However, some of the areas with lowest accessibility also are very important for conservation. Roadless areas have a higher eco- logical value, given that some of them are among the most pristine ecosystems on Earth [10]. Furthermore, endemic species are particularly frequent in small islands and mountains [11± 13], but these also are among the areas with lowest accessibility [8, 9, 14]. Improving biodiver- sity information in these remote areas is a conservation priority that is only seldom achieved. Among the European vertebrates, the Aeolian wall lizard Podarcis raffonei (Mertens, 1952) is among the species with the smallest geographic distribution [15], and one of the most threatened by extinction [16]. This lizard is endemic of the Aeolian Archipelago in Southern Italy; currently, it is only reported from three tiny islets, and from a small peninsula of the Vulcano island [see methods, Fig 1 and Table 1; 16±18]. None of these areas is easily accessible. Despite some studies and reviews performed on this species [16, 18±23], a regular monitoring program is still lacking. Nevertheless, this lizard is considered to have suffered a dramatic decline during the last decades, and the IUCN Red List suggests a decreasing population trend [24]. Habitat loss, urbanization, wildfires, overgrazing, and inbreeding have all been proposed as potential driv- ing factors [18, 19, 24±28]. It has been suggested that historical declines of P. raffonei might be related with the expansion of the Italian wall lizard P. siculus [18, 19], which has been intro- duced across the whole Mediterranean basin and adjacent areas, as well as in the UK and the US and Canada, by human activities [29, 30]. The competition with this introduced lizard is thus a possible driver of the decline of P. raffonei [28]. In fact, experimental evidence suggests that P. siculus is more aggressive, more exploratory, bolder, more neophilic and more efficient at finding and exploiting food resources than several native Podarcis species [31±33]. Further- more, hybrids between P. raffonei and P. siculus have been observed in nature [34], suggesting that hybridization might be a further threat. Nevertheless, the causes of the decline of P. raffo- nei are not fully understood, because of the limited amount of data available for testing the proposed hypotheses. Finally, morphological identification of wall lizards is complicated by their high intraspecific diversity, both in shape and colouration, and by strong phenotypic plasticity, with some species showing significant changes of colour pattern across populations, ontogenically or throughout the year [35, 36]. Given the rapidity of the decline of P. raffonei in the Vulcano island, and the small size of extant populations, frequent monitoring is pivotal to assess the status of populations, to PLOS ONE | https://doi.org/10.1371/journal.pone.0253631 June 23, 2021 2 / 15 PLOS ONE Status of Podarcis raffonei on Vulcano Fig 1. Distribution of the Aeolian wall lizard Podarcis raffonei. Distribution of the extant populations of Podarcis raffonei. The figure has been drawn by GFF on the basis of public domain shapefiles at http://www.naturalearthdata. com/. https://doi.org/10.1371/journal.pone.0253631.g001 evaluate the driving factors and to identify prompt management strategies. The aim of this study was examining the fate of the Vulcano population, i.e. the population occupying the larg- est habitat patch where the Aeolian wall lizard still survives [28; see