SPECIATIONAL HISTORY IN A DIVERSE CLADE OF HABITAT-SPECIALIZED SPIDERS (ARANEAE, NESTICIDAE, NESTICUS) - INFERENCES FROM GEOGRAPHIC-BASED SAMPLING

This paper summarizes the results of an initial effort to reconstruct the speciational history of cave spiders (Nesticus) from the southern Appalachian Mountains of eastern North America. The Appalachian Nestic us fauna includes a large series of about 30 species distributed acros s islandlike cave and montane habitats. Many of the species are geogra phically restricted; all of the species are found in allopatry. Observ ed patterns of morphological variation and biogeographic evidence sugg est that species diversification in this lineage may have occurred rec ently, perhaps in response to Pleistocene climatic fluctuations. To ad dress questions about the spatial and temporal dynamics of Nesticus sp eciation, while accounting for potential phylogenetic difficulties, I have gathered nuclear and mitochondrial DNA sequences for a sample of individuals from 81 populations representing 28 Nesticus species. Anal yses of these data indicate that considerable genetic divergence exist s within and among currently recognized morphological species. Consist ent with relatively deep species divergences, most of which likely pre date the Pleistocene, is a prevailing pattern of phylogenetic concorda nce between taxonomic species and monophyletic gene tree lineages. The few deviations from monophyly detected can be tentatively attributed to a peripatric mode of speciation. Although species limits as inferre d by the molecular data ale generally concordant with patterns of morp hological continuity and discontinuity in genitalia, there is evidence to suggest that cryptic phylogenetic lineages exist within some morph ologically continuous units. This observation, in combination with the general depth of species lineages, makes any argument about rapid evo lution in Nesticus genitalic characteristics necessary.