Cryptic speciation, genetic diversity and gene flow in the California turret spider Atypoides riversi (Araneae: Antrodiaetidae)

Populations of the turret spider Atypoides riversi from eight central Californian sites were compared based on variation at ten allozyme loci. Multidimensional scaling of interpopulation genetic distances defined four population units (Coast Range, Sierran, Valley, Jenness Camp), corroborating the distinctness of Coast Range and Sierran populations indicated by a prior study. While the species status of these units has yet to be determined, Jenness Camp is the most likely to represent a new species, given its clear genetic uniqueness (two fixed allelic differences). Populations in all units were generally in Hardy–Weinberg equilibrium with no evidence of inbreeding, though variability was minimal (mean Ho = 2.8%, mean P = 15.4%). Reduced variability in these populations may be the result of repeated bottlenecks, environmental homogeneity, and/or directional selection. Interpopulation differentiation within units was significant in the absence of intervening forest habitat and was substantially less in its presence, indicating that gene flow is likely only when forest corridors exist. To foster preservation of the existing gene pool and enhance participation in it, management of the units of At. riversi should focus on maintaining as many populations in situ as possible and facilitating connections between them, while also creating or restoring habitat for potential colonization. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 82, 27–37.