Testing population genetic structure using parametric bootstrapping and M IGRATE-N

We present a method for investigating genetic population structure using sequence data. Our hypothesis states that the parameters most responsible for the formation of genetic structure among different populations are the relative rates of mutation (μ) and migration (M). The evolution of genetic structure among different populations requires rates of M ≪ μ because this allows population-specific mutation to accumulate. Rates of μ ≪ M will result in populations that are effectively panmictic because genetic differentiation will not develop among demes. Our test is implemented by using a parametric bootstrap to create the null distribution of the likelihood of the data having been produced under an appropriate model of sequence evolution and a migration rate sufficient to approximate panmixia. We describe this test, then apply it to mtDNA data from 243 plethodontid salamanders. We are able to reject the null hypothesis of no population structure on all but smallest geographic scales, a result consistent with the apparent lack of migration in Plethodon idahoensis . This approach represents a new method of investigating population structure with haploid DNA, and as such may be particularly useful for preliminary investigation of non-model organisms in which multi-locus nuclear data are not available.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42796/1/10709_2004_Article_8358.pd

Comparative phylogeography of mutualists and the effect of the host on the genetic structure of its partners.

Whether or not species participating in specialized and obligate interactions display similar and simultaneous demographic variations at the intraspecific level remains an open question in phylogeography. In the present study, we used the mutualistic nursery pollination occurring between the European globeflower Trollius europaeus and its specialized pollinators in the genus Chiastocheta as a case study. Explicitly, we investigated if the phylogeographies of the pollinating flies are significantly different from the expectation under a scenario of plant-insect congruence. Based on a large-scale sampling, we first used mitochondrial data to infer the phylogeographical histories of each fly species. Then, we defined phylogeographical scenarios of congruence with the plant history, and used maximum likelihood and Bayesian approaches to test for plant-insect phylogeographical congruence for the three Chiastocheta species. We show that the phylogeographical histories of the three fly species differ. Only Chiastocheta lophota and Chiastocheta dentifera display strong spatial genetic structures, which do not appear to be statistically different from those expected under scenarios of phylogeographical congruence with the plant. The results of the present study indicate that the fly species responded in independent and different ways to shared evolutionary forces, displaying varying levels of congruence with the plant genetic structur

The GlueX beamline and detector

The GlueX experiment at Jefferson Lab has been designed to study photoproduction reactions with a 9-GeV linearly polarized photon beam. The energy and arrival time of beam photons are tagged using a scintillator hodoscope and a scintillating fiber array. The photon flux is determined using a pair spectrometer, while the linear polarization of the photon beam is determined using a polarimeter based on triplet photoproduction. Charged-particle tracks from interactions in the central target are analyzed in a solenoidal field using a central straw-tube drift chamber and six packages of planar chambers with cathode strips and drift wires. Electromagnetic showers are reconstructed in a cylindrical scintillating fiber calorimeter inside the magnet and a lead-glass array downstream. Charged particle identification is achieved by measuring energy loss in the wire chambers and using the flight time of particles between the target and detectors outside the magnet. The signals from all detectors are recorded with flash ADCs and/or pipeline TDCs into memories allowing trigger decisions with a latency of 3.3 . The detector operates routinely at trigger rates of 40 kHz and data rates of 600 megabytes per second. We describe the photon beam, the GlueX detector components, electronics, data-acquisition and monitoring systems, and the performance of the experiment during the first three years of operation