A multi-layered approach uncovers overlooked taxonomic and physiological diversity in Alpine subterranean spiders (Araneae: Linyphiidae: Troglohyphantes)

The integration of multiple lines of evidence in the delimitation of taxa is becoming the gold standard in modern taxonomy and systematics. Yet, multi-layered taxonomy is still incipient when it comes to species description within mega-diverse group of organisms (e.g., arthropods), especially those inhabiting secluded environments such as caves. This may represent a significant shortcoming, because species in subterranean habitats generally show deep convergence in their somatic traits, perplexing our ability to delimit species via traditional approaches. The genus Troglohyphantes (Araneae: Linyphiidae) is presently known to include 129 species and 5 subspecies, which are primarily distributed in subterranean habitats of the European mountain ranges. Recent studies on Italian Alpine species covered taxonomy and faunistics, biogeography, and ecology. However, our knowledge about the actual species diversity of Troglohyphantes spiders is far from being complete, and it is expected that significant levels of overlooked diversity should exist within the genus. In this work, we combined morphological with target gene molecular data, functional trait analysis, and thermal physiology to explore overlooked diversity in Troglohyphantes vignai aut., a species of subterranean spider in the Western Italian Alps with an apparent broader distribution compared to its congeners. Our approach proved effective in uncovering overlooked diversity and further supporting the split of T. vignai aut. into three distinct species, whose distribution ranges show striking resemblances with that of other subterranean spiders. We here describe the new species and discuss their origin in light of their geographical vicariance, niche convergence, thermal ecology and divergence time.