Patterns of intra- and interspecific diversity in araneomorph spiders of southern high Appalachian leaf litter

The intraspecific diversity of the few mygalomorph spiders in southern Appalachia has received considerable attention, revealing highly localized and deeply divergent populations and in some cases cryptic species. The araneomorph fauna of the region has received comparatively little study, due to its higher diversity, more tentative taxonomy, and perhaps perception that short-range endemicity might be lower. In this study, we examined this last assumption, surveying patterns of intraspecific diversity across Araneomorphae occurring in the leaf litter of high elevation spruce-fir sky islands of southern Appalachia, as revealed by population level metabarcoding. In most species, intraspecific haplotypic diversity, while high, revealed little geographic pattern, generally supporting assumptions of low regional endemicity. Of 50 spider species found in spruce-fir forest litter, more than 30 occur more widely, and showed little sign of subdivision even over major biogeographic features in the region, such as the French Broad River valley. By analyzing 10 of these well-sampled species with population genetic and phylogeographic methods, we found that only a few showed significant population level subdivisions. We suggest that the ballooning behavior of most immature araneomorph spiders is sufficiently frequent to overcome divergence of otherwise isolated populations, and that in those few exceptions the species are more specialized to particular microhabitats in the spruce-fir forest and such unpredictable dispersal may have been selected against.