Phylogeny and Historical Biogeography of the Spider Genus Lutica (Araneae, Zodariidae)

Spiders of the genus Lutica from 19 populations in southern California and Baja California, including all the California Channel Islands except Anacapa, were compared electrophoretically on the basis o f variability at 15 gene loci . Fixed allelic differences clearly define two species : new species A [Santa Barbara an d Ventura Counties, northern Channel Islands (San Miguel, Santa Rosa, Santa Cruz), southern Channel Island s (San Nicolas, Santa Barbara, Santa Catalina)] and new species C [Guerrero Negro, central Baja California], whil e morphological features define two others: new species B [Los Angeles, Orange and San Diego Counties, northern Baja California] and clementea [San Clemente Island] . Phylogenetic analysis of the electrophoretic data using a variety of methods revealed that evolutionary rates among the populations sampled have been very unequal . The phylogenetic relationships among populations consistently supported by the electrophoretic cladogram s generally correspond with the geological history of the Channel Islands and adjacent mainland and suggest certain likely colonization events involving some of the islands . Genetic similarities and differences among populations can be used to assess specific hypotheses about biogeography and evolution . Populations on islands are especially useful because they frequently are discrete entities with little gene flow among islands ; for some island s the geologic history also is known . This type of analysis is especially powerful for sedentary species in which chances for dispersal among populations are minimal (Carlquist 1981) . The California Channel Islands are an excel lent system for addressing questions of evolutionary and biogeographic history . These eigh t islands vary in size, topography and physical isolation (Fig. 1) . While the geologic history of th e islands and their surroundings is complex, it ha s clearly involved the northward transport of thes e island landmasses on crustal blocks (terranes) caught in the tectonics of the Pacific/Nort h American plate margin (Hornafius et al . 1986) . It has also involved extensive changes in sea leve l which have repeatedly submerged some islands while possibly leaving the highest areas of others continuously above water since the Oligocen e (Vedder & Howell 1980 ; Haq et al . 1987) . Biogeographic studies of biologically old taxa on th e Channel Islands need to consider both vicariance and dispersal as factors in producing contemporary distributional patterns. The spider family Zodariidae and many of it s genera have existed since at least the Oligocene (Petrunkevitch 1942, 1952) and they have been exposed to the geological and climatic changes of the last 30 million years . Worldwide, 47 genera have been described, mainly from the tropical and temperate regions of the Old World (Jocque 1991) . Spiders of the genus Lutica are the only native representatives of the Zodariidae i n the continental United States and they live i n restricted insular and coastal dune communitie s in southern California and Baja California, including all the California Channel Islands excep t Anacapa (Ramirez 1995) . Their preferred habitat is a sand dune covered by native beach vegetation located well behind the high tide line an d the influence of sea water (Gertsch 1961 ; Ramirez 1995) . On Santa Barbara Island, typical coastal dunes do not exist and these spiders liv e in the sandy soil and debris below vegetatio n growing on a sea cliff (Ramirez 1995) . They live in silk-lined burrows they construct in the sand , emerging only at night to feed and, during August-October, to mate (Gertsch 1961 ; Ramire z 1995) . When dislodged from their burrows, thes e