Meta menardi and M. bourneti (Araneae: Tetragnathidae) segregate along the altitudinal gradient of Mount Etna (Sicily, S–Italy)

Meta menardi (Latreille, 1804) and M. bourneti Simon, 1922 (Araneae: Tetragnathidae) are ubiquitous inhabitants of the twilight zone of most hypogean sites across Europe. Recent observations in volcanic caves pointed out the presence of both species in Sicily, with M. menardi occurring in a small number of caves. On the basis of field investigations conducted in 2017–2021, we analyzed the distribution and the habitat frequency of the two species along the altitudinal gradient of Mount Etna. Our results demonstrate a significant effect of climate and altitude on the segregation of the two species, with M. menardi occurring exclusively above 1200 meters in caves opening in areas characterized by low temperatures (mean ± SD = 10.1 ± 0.688C) and high precipitations (682 ± 19 mm). Conversely, M. bourneti preferably occurred in areas with higher temperatures (14.5 ± 2.18C) and lower precipitations (606 ± 46 mm). Substrate age was not affecting the distribution of the two species, as both occurred in volcanic caves of ancient and recent formation (from 350 to .1,000 years). In light of the ongoing global warming, a possible increase in temperature could favor the upshift of M. menardi towards upper areas on the volcano subjected to high volcanic disturbance and thus unsuitable for hosting stable populations through time. In this regard, investigations on the response of Meta spiders to increases in temperature on the Etna volcano would be an asset to establish an appropriate management plan for the conservation of the newly discovered population of M. menardi in Sicily.