Population structure and dispersal in a patchylandscape: nuclear and mitochondrial markers revealarea effects in the spider Theridion californicum(Araneae: Theridiidae)

摘要

Changes in land use have a major effect on patterns of biodiversity. However, few studies have examined thedemographic and genetic shifts associated with a return to semi-natural habitat following extended periods ofhuman disturbance. Here we examine patterns of population structure in a spider restricted to the Pacific coastalstrip of North America that exhibits an exuberant colour polymorphism. We use mitochondrial DNA and AFLPmarkers to examine genetic structure and estimate gene flow. The results show contrasting, gender-specificpatterns between these markers that suggest limited dispersal, combined with area effects most likely caused byexpansion from refugial habitat patches following land-management changes in a region of the San Francisco EastBay. Colour-morph frequencies are not correlated with this complex genetic structure. Thus, unlike the classicalarea effects that were based on colour morphs, we demonstrate in T. californicum signals of historical contingencyat neutral loci but not at the Colour locus, where traces of past events have been obliterated by balancingselection.