MICROGEOGRAPHIC VARIATION IN MITOCHONDRIAL DNA OF MEADOW VOLES (MICROTUS PENNSYLVANICUS) IN RELATION TO POPULATION DENSITY

We examined mitochondrial-DNA (mtDNA) sequence heterogeneity on four adjacent trapping grids in an island population of meadow voles (Microtus pennsylvanicus) at two different population densities. Four restriction endonucleases revealed 20 different mtDNA composite phenotypes in samples totaling 198 meadow voles. There were significant heterogeneities in the distribution of four common mtDNA composite phenotypes among the four trapping grids, suggesting that there is population subdivision on a fine scale. Genetic distances between grids, mtDNA diversity within grids, and G_ST also varied during the study period. We found a decrease in genetic distance and an increase in diversity when the population density was high and vice versa when the population density was low. When population density was high, the coefficient of gene differentiation was smaller than the same coefficient observed when the population density was low. These changes in population subdivision and diversity are consistent with theoretical expectations of population structure in which effective female population size and dispersal are the critical variables. The data also support the hypothesis of maintenance of mtDNA diversity by population subdivision, rapid population growth rate, and dispersal.

GEOGRAPHIC DISTRIBUTION AND BIOGEOGRAPHY OF REPRESENTATIVE SPECIES OF XERIC GRASSLAND-ADAPTED NEARCTIC LYGAEIDAE IN WESTERN NORTH AMERICA (INSECTA: HETEROPTERA)

This paper outlines the known distribution of eight xeric grassland-adapted species of Lygaeidae, and examines these distributions with respect to the glacial history of North America during the Pleistocene, and past and present distribution of grassland vegetation. Four of these species (Neosuris castanea, Sisamnes claviger, Ligyrocoris latimarginatus, and Melanopleurus perplexus) probably survived the Pleistocene in refugia south of the Late Wisconsinan ice sheet. Differences in climatic requirements may explain the variations in geographic distribution exhibited by these four insects and a methodology for testing this is discussed. The four other species (Crophius ramosus, Kolenetrus plenus, Slaterobius insignis, and Emblethis vicarius) may have occurred in the north prior to 1.2 mya and survived the Late Pleistocene in both the northern Beringian refugium and in southern refugia. Molecular systematics, especially use of DNA restriction site or sequence data, might provide the evidence needed to test historical biogeographic postulates based on the extant distribution of these species.

Beringian origins and cryptic speciation events in the fly agaric (Amanita muscaria)

Amanita muscaria sensu lato has a wide geographic distribution, occurring in Europe, Asia, Africa, Australia, New Zealand, and North, Central and South America. Previous phylogenetic work by others indicates three geographic clades (i.e. 'Eurasian', 'Eurasian-alpine' and 'North American' groups) within A. muscaria. However, the historical dispersal patterns of A. muscaria remained unclear. In our project, we collected specimens from arctic, boreal and humid temperate regions in Alaska, and generated DNA sequence data from the protein-coding beta-tubulin gene and the internal transcribed spacer (ITS) and large subunit (LSU) regions of the ribosomal DNA repeat. Homologous sequences from additional A. muscaria isolates were downloaded from GenBank. We conducted phylogenetic and nested clade analyses (NCA) to reveal the phylogeographic history of the species complex. Although phylogenetic analyses confirmed the existence of the three above-mentioned clades, representatives of all three groups were found to occur sympatrically in Alaska, suggesting that they represent cryptic phylogenetic species with partially overlapping geographic distributions rather than being allopatric populations. All phylogenetic species share at least two morphological varieties with other species, suggesting ancestral polymorphism in pileus and wart colour pre-dating their speciations. The ancestral population of A. muscaria likely evolved in the Siberian-Beringian region and underwent fragmentation as inferred from NCA and the coalescent analyses. The data suggest that these populations later evolved into species, expanded their range in North America and Eurasia. In addition to range expansions, populations of all three species remained in Beringia and adapted to the cooling climate.