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Patterns of inheritance: defining geographical barriers of the spider Mimetus hesperus (Araneae; Mimetidae) along the Sierra Nevada Mountains
The purpose of this study is to compare the genetic distances of Mimetus hesperus and Theridion neomexicanum within and between the San Joaquin Valley and Mojave Valley regions. To my best knowledge this is the first genetic study of M. hesperus. Mountains and distance are well known barriers to gene flow in species with lower vagility. For short lived spiders, the only non-synanthropic transport method over mountains is ballooning. Ballooning spiders rely on surface area for lift, and larger spiders have a difficult time sustaining flight as they have less surface area per unit weight. M. hesperus hunts other spiders and probably has large spiderlings which make it difficult to balloon from hatching. With insufficient ballooning the Sierra Nevada Mountains should act as a barrier to gene flow for M. hesperus. I predict that comparisons between populations of M. hesperus on the same side of the Sierra Nevada Mountains will show smaller genetic distances than comparisons between populations on opposite sides of the mountains. M. hesperus and T. neomexicanum were collected from sites around the Sierra Nevada Noubtains and either died of natural causes or were humanely euthanized in <0°C ethanol. DNA was extracted and PCR was run to amplify the cytochrome oxidase 1 sununit c gene. Amplified sequences were run in two percent agaorse gel to look for banding of appropriate length and gels showing target band were purified and sent to the University of Florida for sequencing. All other bands were heavily troubleshooted and re amplified Sequence chromatograms were analyzed to ensure only pure sequences were used in analysis. Insufficient numbers of T. neomexicanum were resolved so they were used as outgroups in analyzing M. hesperus. Sequences were aligned using clustalW and cut in MEGA to ensure accurate comparisons. Pairwise distances were calculated between all specimens. A neighbor joining tree was calculated, and overall percent divergence based on collection sites, and tree groupings was computed. Character based maximum parsimony and maximum likelihood trees were calculated to confirm results seen in neighbor joining analysis. Haplotype diversity was shown by grouping all single nucleotide polymorphisms for comparison of haplotypes and by collection site and tree groupings. Genetic distance and trees reveal three distinct groupings of M. hesperus, but a permutation test found distance within populatioins from both sides insignificant, so all specimens were grouped as either east or west of the mountains. Although anecdotal at best, haplotype diversity hints that M. hesperus may have brached from the west to the east. The Sierra Nevada Mountains appear to separate populations of M. hesperus in the Central Valley and in the Mojave more than distance alone. M. hesperus populations collected over 100 miles apart on the west side of the mountains showed no significant divergence, indicating some unknown mechanism of gene flow linking these populations, but a larger sample size is needed to confirm this.
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