Aptostichus simus is a trapdoor spider endemic to the coastal dunes of central and southern California and, on morphological grounds, is recognized as a single species. Mitochondrial DNA 16S rRNA sequences demonstrate that most populations are fixed for the same haplotype and that the population haplotypes from San Diego County, Los Angeles County, Santa Rosa Island, and Monterey County are extremely divergent (6-12%), with estimated separation times ranging from 2 to 6 million years. A statistical cluster analysis of morphological features demonstrates that this genetic divergence is not reflected in anatomical features that might signify ecological differentiation among these lineages. The species status of these divergent populations of A. simus depends upon the species concept utilized. If a time-limited genealogical perspective is employed, A. simus would be separated at the base into two genetically distinct species. This study suggests that species concepts based on morphological distinctiveness, in spider groups with limited dispersal capabilities, probably underestimate true evolutionary diversity.

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 H o = 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.

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Magnetic heading (direction the spider's ventrum faced) and web inclination (degree of slant from the vertical) in Argiope trifasciata Forskal, a diurnal orb-weaving spider, were studied at a coastal site in southern California for nine weeks in fail 1999. Throughout the study, A. trifasciata largely occupied east-west oriented webs with their venters facing south and southwest. Mean magnetic heading was unaffected by ambient temperature extremes. Inclination levels varied from week to week over an approximately 5° range. However, these changes followed no discernible pattern and were independent both of the sun's decrease in maximum altitude during the course of the study and of magnetic heading. Since the ventrum of A. trifasciata is dark, the consistent southern orientation exhibited by spiders at our study site suggests that they sought to maximize solar radiation in an attempt to gain heat. In addition, the east-west, facing-the-sun orientation of webs at this site places them parallel to the prevailing western breezes, minimizing their exposure to wind disturbance. As for inclination, it is unclear what factors may be influencing the degree of slant in A. trifasciata webs and further study will be needed to ascertain what they might be.

In this study, we analyse genetic structure among ten isolated populations of a sedentary burrowing wolf spider, Geolycosa pikei, collected from Long Island, New York barrier islands. Using allozyme electrophoresis to estimate gene frequencies at 12 loci, only four loci were polymorphic (i.e. Aat, Apk, Gpi, Idh‐1), and populations showed little differentiation (mean Fsr=0.020). Contrary to stepping‐stone model predictions, the matrix of genetic distances among sites was not significantly associated with the physical distance matrix, which suggests that G. pikei on Long Island barriers does not adhere to a stepping‐stone model. Geolycosa pikei may be better dispersers than previously estimated and/or the ephemeral quality of the inlets may not allow for the development of significant inter‐populational genetic differences. In addition, geologic evidence suggests that these barriers became relatively stable only 8000 BP. Therefore, these habitats have been only recendy colonized, which may result in low genetic variability and inter‐populational differentiation possibly due to genetic drift from repeated and prolonged bottlenecks during recolonization (i.e. founder events).

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Abstract. The relationship between individual heterozygosity and characteristics likely to be associated with fitness was investigated in the labyrinth spider Metepeira ventura. Adult females and their egg sacs were collected at a coastal site in southern California, and three measures of bodily condition (carapace width, weight, residual index) and six measures of reproductive output (number of egg sacs, variation in egg number among sacs [coefficient of variation], total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were determined for each spider. The sample was polymorphic at three allozyme loci that were in Hardy–Weinberg equilibrium, and individual females were heterozygous at up to two of the three loci, forming three heterozygosity classes (0, 1, and 2). None of the bodily condition measures were significantly related to the number of heterozygous loci, while four of the reproductive output estimators (total number of eggs, mean eggs/sac, mean eggs/sac divided by carapace width, mean eggs/sac divided by weight) were significantly influenced by heterozygosity. In each significant case, values for class 2 females were less than those for class 0 and 1 females, whose values were usually more similar. Thus, while female bodily condition was comparable among classes, the most heterozygous females produced fewer total eggs and eggs per sac than their less heterozygous peers. The fact that females of M. ventura engage in a reproductive investment‐number trade‐off suggests that high‐variability and low‐variability females may be pursuing distinct reproductive strategies in the wild, with more heterozygous females being K‐selected (smaller clutches, heavier eggs) and more homozygous females being r‐selected (larger clutches, lighter eggs). Further investigation will be needed to assess more fully the fitness value of heterozygosity in M. ventura.