Local- versus broad-scale environmental drivers of continental ß-diversity patterns in subterranean spider communities across Europe.

Macroecologists seek to identify drivers of community turnover (ß-diversity) through broad spatial scales. However, the influence of local habitat features in driving broad-scale ß-diversity patterns remains largely untested, owing to the objective challenges of associating local-scale variables to continental-framed datasets. We examined the relative contribution of local- versus broad-scale drivers of continental ß-diversity patterns, using a uniquely suited dataset of cave-dwelling spider communities across Europe (35-70° latitude). Generalized dissimilarity modelling showed that geographical distance, mean annual temperature and size of the karst area in which caves occurred drove most of ß-diversity, with differential contributions of each factor according to the level of subterranean specialization. Highly specialized communities were mostly influenced by geographical distance, while less specialized communities were mostly driven by mean annual temperature. Conversely, local-scale habitat features turned out to be meaningless predictors of community change, which emphasizes the idea of caves as the human accessible fraction of the extended network of fissures that more properly represents the elective habitat of the subterranean fauna. To the extent that the effect of local features turned to be inconspicuous, caves emerge as experimental model systems in which to study broad biological patterns without the confounding effect of local habitat features.

Continental data on cave-dwelling spider communities across Europe (Arachnida: Araneae).

BACKGROUND: Spiders (Arachnida: Araneae) are widespread in subterranean ecosystems worldwide and represent an important component of subterranean trophic webs. Yet, global-scale diversity patterns of subterranean spiders are still mostly unknown. In the frame of the CAWEB project, a European joint network of cave arachnologists, we collected data on cave-dwelling spider communities across Europe in order to explore their continental diversity patterns. Two main datasets were compiled: one listing all subterranean spider species recorded in numerous subterranean localities across Europe and another with high resolution data about the subterranean habitat in which they were collected. From these two datasets, we further generated a third dataset with individual geo-referenced occurrence records for all these species. NEW INFORMATION: Data from 475 geo-referenced subterranean localities (caves, mines and other artificial subterranean sites, interstitial habitats) are herein made available. For each subterranean locality, information about the composition of the spider community is provided, along with local geomorphological and habitat features. Altogether, these communities account for > 300 unique taxonomic entities and 2,091 unique geo-referenced occurrence records, that are made available via the Global Biodiversity Information Facility (GBIF) (Mammola and Cardoso 2019). This dataset is unique in that it covers both a large geographic extent (from 35° south to 67° north) and contains high-resolution local data on geomorphological and habitat features. Given that this kind of high-resolution data are rarely associated with broad-scale datasets used in macroecology, this dataset has high potential for helping researchers in tackling a range of biogeographical and macroecological questions, not necessarily uniquely related to arachnology or subterranean biology.

The first karyotype study in palpigrades, a primitive order of arachnids (Arachnida: Palpigradi).

Chromosomes of palpigrades (Arachnida: Palpigradi), a rare arachnid order with numerous primitive characters, were studied for the first time. We analysed two species of the genus Eukoenenia, namely E. spelaea and E. mirabilis. Their karyotypes are uniform, consisting of a low number of tiny chromosomes that decrease gradually in size. Study of the palpigrade karyotype did not reveal morphologically differentiated sex chromosomes. Analysis of E. spelaea showed that constitutive heterochromatin is scarce, GC-rich, and restricted mostly to presumed centromeric regions. Meiosis is remarkable for the presence of a short diffuse stage and prominent nucleolar activity. During prophase I, nuclei contain a large nucleolus. Prominent knob at the end of one bivalent formed by constitutive heterochromatin is associated to the nucleolus by an adjacent NOR. Presence of a nucleolus-like body at male prophase II suggests activity of NOR also during beginning of the second meiotic division. The data suggest acrocentric morphology of palpigrade chromosomes. Palpigrades do not display holocentric chromosomes which appear to be apomorphic features of a number of arachnid groups. These are: acariform mites, buthid scorpions, and spiders of the superfamily Dysderoidea. Therefore, cytogenetic data do not support a close relationship of palpigrades and acariform mites as suggested previously.