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A Phylogenetic analysis of Vaejovis confusus in California: the effects of anthropogenic factors on genetic divergence
The purpose of this study is to investigate the level of genetic divergence among populations of Vaejovis confusus in the southern San Joaquin Valley and across the state of California. Although there has been considerable research to measure genetic variation among and within scorpion species, little work has been done to investigate the impact of anthropogenic factors on genetic variation within populations. Anthropogenic factors such as man-made barriers can fragment populations and may serve as mechanisms of reproductive isolation. Particularly in the southern San Joaquin Valley, vast arrays of canals and artificial channels have been constructed to divert water from the Kern River for agricultural purposes. In the southern San Joaquin study, the level of genetic divergence is examined in a fragmented population as a result of an anthropogenic barrier, the California Aqueduct, at Coles Levee Ecosystem Preserve. Sequencing of the mitochondrial 16S ribosomal RNA gene in 20 Vaejovis confusus individuals of each fragmented population was performed. Neighbor-joining and maximum parsimony analysis of DNA sequences elucidated the level of genetic divergence. For comparison, an identical analysis was performed across a natural barrier, the Kern River at the Panorama Vista Preserve, which has separated Vaejovis confusus populations for a much longer period of time. The results of this study showed the presence of five haplotypes at the Coles Levee Ecosystem Preserve, with three haplotypes common to both sides of the California Aqueduct. Similarly at Panorama Vista Preserve, five haplotypes were found, with two haplotypes shared at both field sites across the Kern River. These results indicate that scorpion populations across the California Aqueduct and Kern River are not genetically partitioned, despite the isolating effect of these barriers. The existence of the California Aqueduct for over 50 years is not enough time to cause genetic divergence among fragmented populations. The occasional drying of the Kern River may promote gene flow between the populations or amount of time after reproductive isolation may be insufficient to cause evolutionary divergence between the two populations. In the California analysis the mitochondrial 16S rRNA gene is examined in 22 individuals from 9 counties to determine the effects of isolation by distance on the geographic-genetic structure of Vaejovis confusus populations. Scorpions were obtained from a collection of samples from the California Academy of Sciences, San Francisco. Neighbor-joining and maximum parsimony analyses were used to resolve the level of evolutionary relatedness among the populations of Vaejovis confusus throughout California. Fourteen haplotypes were found in this analysis. Eleven haplotypes were unique to their field site, whereas three were common across the state across large geographic distances (approximately 350 miles). Mitochondrial markers found high genetic variation (9.6%) in this species. Nearly half (154/325) of pairwise distance comparisons showed a 2.0% or higher sequence divergence and supported an overall isolation by distance effect. The occurrence of three haplotypes across the state results in a weak association between geography and genetic structure of V. confusus. Notably however, there is some geographic partitioning between haplotype D common in western California and haplotypes A and C common in eastern California. However, the overall lack of genetic partitioning with respect to geography among the California populations is likely due to an insufficient amount of elapsed time to promote genetic differentiation.
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