Climbing on the La Canna Volcanic Sea Stack to Obtain First-Hand Data on the Tiniest Population of the Critically Endangered Aeolian Wall Lizard Podarcis raffonei

SIMPLE SUMMARY: Information about the status and trends of endangered species populations are vital for conservation actions, yet these data are often limited for those inhabiting remote and difficult-to-access areas. With the technical support of an alpine guide, I climbed on La Canna sea stack, a columnar volcanic pinnacle 70 m high, to gather information on the size, morphology, and genetic variability of the tiniest population of the critically endangered Aeolian wall lizard Podarcis raffonei. Results indicate a current population size of about a hundred individuals, a body size of lizards significantly larger than previously known, and a complete lack of genetic diversity. Cephalic malformations observed on all captured individuals indicate the detrimental effect of inbreeding depression and represent a severe threat to the persistence of this population. ABSTRACT: Among the extant populations of the critically endangered Aeolian wall lizard, the most vulnerable is the one surviving on La Canna, a columnar volcanic stack off the Filicudi Island. Here, I report the results of the first climbing expedition by a biologist on La Canna, that contributed direct observations and updated information on the size, morphology, and genetic variability of this population. Lizard density at the sampling site (a small terrace at 50 m of elevation) was 1.7 m(−2), twice of a previous estimate. Standard methods for estimating population size are unsuitable for La Canna. An educated guess of about a hundred individuals can be drawn, considering the extent of habitat available on the stack and the number of observed lizards. Lizards on La Canna were not fearless, despite what was reported by alpinists, possibly because of aggressive intraspecific interactions or high environmental temperatures during sampling. Biometric data significantly extend the body size of La Canna’s lizards and indicate that it is not smaller than other P. raffonei populations. A complete lack of genetic diversity was found at the mitochondrial nd4 gene, in line with previous allozyme data and with estimates on other microinsular Podarcis populations. The small size of the La Canna population implies severe genetic drift and an extremely high level of inbreeding, as supported by low heterozygosity found across the genome. Detrimental effects of inbreeding depression are evident as cephalic malformations observed in all captured lizards of La Canna and might represent the more immediate threat to the persistence of this population.