Another brick in the wall of European subterranean spider knowledge: adding Macaronesian species and their traits to the picture

Diego Patiño-Sauma, Pedro Cardoso, Pedro Oromì, Paulo A. V. Borges, Adrià Bellvert, Luís Carlos Crespo, Isabel R. Amorim, Karla Tolić, Martina Pavlek, Giuseppe Nicolosi , Nuria Macías-Hernández, Stefano Mammola 

Caves and other subterranean ecosystems impose highly selective environmental filters, driving the evolution of convergent and specialized traits in subterranean organisms. Here, we present the first comprehensive checklist and trait database for subterranean spiders of Macaronesia, thereby filling a significant knowledge gap relative to continental Europe. We compiled data through direct morphological measurements and literature review, covering 64 morphological and ecological traits for 61 species (14 families) from Macaronesia, along with 66 additional species in continental Europe not included in the previous checklist. After accounting for taxonomic changes, the checklist of European subterranean spiders now lists 637 species, of which 278 are considered to be obligate subterranean-dwellers (troglobionts). Functional trait analyses using n-dimensional hypervolumes revealed moderate overlap in the functional space of continental Europe and Macaronesian subterranean spiders (β_total = 0.47), driven primarily by differences in trait richness rather than the replacement of functional space, with the Macaronesian spiders occupying a smaller functional space than the continental European ones. The Macaronesian assemblage showed more regular (even) niche occupation but similar overall functional dispersion compared to Europe, suggesting lower functional redundancy yet comparable trait diversity. These findings suggest that similar environmental pressures drive functional convergence in cave faunas despite geographic, geological (karstic vs. volcanic), and taxonomic differences. The expanded trait database is a valuable resource for ecological and conservation research, highlighting the need for continued exploration and protection of subterranean biodiversity on oceanic islands.