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Aim Kangaroo mice, genus Microdipodops Merriam, are endemic to the Great Basin and include two species: M. pallidus Merriam and M. megacephalus Merriam. The pallid kangaroo mouse, M. pallidus, is a sand-obligate desert rodent. Our principal intent is to identify its current geographical distribution and to formulate a phylogeographical hypothesis for this taxon. In addition, we test for orientation patterns in haplotype sharing for evidence of past episodes of movement and gene flow.Location The Great Basin Desert region of western North America, especially the sandy habitats of the Lahontan Trough and those in south-central Nevada.Methods Mitochondrial DNA sequence data from portions of three genes (16S ribosomal RNA, cytochrome b, and transfer RNA for glutamic acid) were obtained from 98 individuals of M. pallidus representing 27 general localities sampled throughout its geographical range. Molecular sequence data were analysed using neighbour-joining, maximum-parsimony, maximum-likelihood and Bayesian methods of phylogenetic inference. Directional analysis of phylogeographical patterns, a novel method, was used to examine angular measurements of haplotype sharing between pairs of localities to detect and quantify historical events pertaining to movement patterns and gene flow.Results Collecting activities showed that M. pallidus is a rather rare rodent (mean trapping success was 2.88%), and its distribution has changed little from that determined three-quarters of a century ago. Two principal phylogroups, distributed as eastern and western moieties, are evident from the phylogenetic analyses (mean sequence divergence for cytochrome b is c. 8%). The western clade shows little phylogenetic structure and seems to represent a large polytomy. In the eastern clade, however, three subgroups are recognized. Nine of the 42 unique composite haplotypes are present at two or more localities and are used for the orientation analyses. Axial data from haplotype sharing between pairwise localities show significant, non-random angular patterns: a north-west to south-east orientation in the western clade, and a north-east to south-west directional pattern in the eastern clade.Main conclusions The geographical range of M. pallidus seems to be remarkably stable in historical times and does not show a northward (or elevationally upward) movement trend, as has been reported for some other kinds of organism in response to global climate change. The eastern and western clades are likely to represent morphologically cryptic species. Estimated times of divergence of the principal clades of M. pallidus (4.38 Ma) and between M. pallidus and M. megacephalus (8.1 Ma; data from a related study) indicate

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Genetic variation among populations of chewing lice (Geomydoecus actuosi) was examined in relation to chromosomal and electrophoretic variation among populations of their hosts (Thomomys bottae) at a contact zone. Louse demes were characterized by low levels of genetic heterozygosity (H̄ = 0.039) that may result from founder effects during primary infestation of hosts, compounded by seasonal reductions in louse population size. Louse populations sampled from different hosts showed high levels of genetic structuring both within and among host localities. Microgeographic differentiation of louse populations is high (mean F = 0.092) suggesting that properties of this host-parasite system promote differentiation of louse populations living on different individual hosts. Among-population differentiation in lice (F = 0.240) was similar to that measured among host populations (F = 0.236), suggesting a close association between gene flow in pocket gophers and gene flow in their lice.