Global distribution of microwhip scorpions (Arachnida: Palpigradi)

Aim: In the era of big data, research on global distribution patterns has mostly concentrated on conspicuous organisms and thus a major proportion of biodiversity on Earth remains unmapped. We examined the global distribution of palpigrades, a poorly-studied group of low dispersive arachnids. We asked what is the typical range size of palpigrades, the ecological factors driving their distributions, and to what extent sampling bias may influence the observed patterns. Location: Global. Taxon: Palpigrades (Arachnida: Palpigradi) in the genus Eukoenenia, tiny Arachnids specialized to subterranean life. Methods: We assembled a global database of over 1,000 localities and referring to 57 soil- and 71 cave-adapted palpigrades. We tested for differences in range sizes of soil- and cave-adapted species. We used logistic regressions to explore the contribution of climate, nutrient availability, and geology in driving observed distributions. Finally, we verified the potential correlation between the number of occurrence records and the number of palpigrades’ researchers. Results and conclusions: We showed that Europe and Brazil are major centers of diversification of cave-adapted palpigrades. Conversely, the diversity of soil-adapted species was distributed over a broader geographic expanse, mainly in the Southern Hemisphere. Both cave and soil species had narrow distribution ranges, with a median value of 0.01 km2; only a few parthenogenetic species were distributed over multiple continents. The distribution of both cave- and soil-adapted palpigrades was primarily explained by climatic conditions, and secondarily by nutrient and habitat availability. In the Alps, the distribution of cave-adapted species also bears the signature of past historical events related to glaciation cycles. There is, however, a pronounced people-species correlation, suggesting that the observed patterns are not generalizable to poorly studied areas. Our analysis represents a first account on palpigrades distribution and ecology, offering a jumping-off point for future studies on the macroecology, distribution, and conservation of these poorly-known organisms.