Tuesday, August 19, 2008

Uncovering genetic divergence and routes of gene exchange in the sand-obligate pallid kangaroo mouse, M. pallidus, from the Great Basin Desert

Kangaroo mice belong to the genus Microdipodops Merriam and are uncommon and rather bizarre-looking rodents, having enormous heads and large hind feet relative to their small (about 10 g) body size. The genus is endemic to the Great Basin of North America and includes two species: M. pallidus Merriam and M. megacephalus Merriam. The pallid kangaroo mouse, M. pallidus, is a sand-obligate desert rodent and this study examines its geographical distribution and formulates a phylogeographical hypothesis. This study also introduces a new analytical tool for testing orientation patterns in haplotype sharing for evidence of past episodes of gene flow.
The study examines mitochondrial DNA sequence data from early 100 individuals of M. pallidus sampled throughout its geographical range. The distribution of M. pallidus appears to be remarkably stable and is virtually unchanged from that determined three-quarters of a century ago. Unlike some other kinds of organism that show distributional adjustments in response to global climate change, there is no northward (or elevationally upward) distributional movement trend detected in M. pallidus.
Phylogenetic analyses show two principal clades, distributed as eastern and western units. The two clades are likely to represent morphologically cryptic species that diverged about 4 Ma. Results of this study (and a related study) now paint a picture of an endemic Great Basin taxon that diverged much earlier than thought previously and well before the creation of the extensive sandy environments during the Pleistocene and Holocene.
The directional analysis of phylogeographic patterns (DAPP analysis) used in this study is novel and may be useful in other studies. DAPP uses angular measurements of haplotype sharing between pairs of localities and circular statistical analyses to detect and quantify historical events pertaining to movement patterns and gene flow. DAPP analyses show significant, non-random angular patterns in both clades of M. pallidus. The phylogeographical patterns described here (both the eastern–western clades and the nonrandom directional patterns) may serve as a model for other sand-obligate members of the Great Basin Desert biota.

Source paper: Hafner, J. C., Upham, N. S., Reddington, E. & Torres, C. W. (2008) Phylogeography of the pallid kangaroo mouse, Microdipodops pallidus: a sand-obligate endemic of the Great Basin, western North America. Journal of Biogeography, doi: 10.1111/j.1365-2699.2008.01942.x.

Source of article: Journal of Biogeography highlighted papers

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