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- Arvelius, S., et al.
(författare)
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Statistical study of relationships between dayside high-altitude and high-latitude O+ ion outflows, solar winds, and geomagnetic activity
- 2005
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 23, s. 1909-1916
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Tidskriftsartikel (refereegranskat)abstract
- The persistent outflows of O+ ions observed by the Cluster CIS/CODIF instrument were studied statistically in the high-altitude (from 3 up to 11 RE) and high-latitude (from 70 to ~90 deg invariant latitude, ILAT) polar region. The principal results are: (1) Outflowing O+ ions with more than 1keV are observed above 10 RE geocentric distance and above 85deg ILAT location; (2) at 6-8 RE geocentric distance, the latitudinal distribution of O+ ion outflow is consistent with velocity filter dispersion from a source equatorward and below the spacecraft (e.g. the cusp/cleft); (3) however, at 8-12 RE geocentric distance the distribution of O+ outflows cannot be explained by velocity filter only. The results suggest that additional energization or acceleration processes for outflowing O+ ions occur at high altitudes and high latitudes in the dayside polar region.
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| 2. |
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| 3. |
- Kuchta, Shawn, et al.
(författare)
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Closing the ring: historical biogeography of the salamander ring species Ensatina eschscholtzii
- 2009
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Ingår i: Journal of Biogeography. - : Wiley. - 1365-2699 .- 0305-0270. ; 36:5, s. 982-995
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Tidskriftsartikel (refereegranskat)abstract
- The salamander Ensatina eschscholtzii Gray is a classic example of a ring species, or a species that has expanded around a central barrier to form a secondary contact characterized by species-level divergence. In the original formulation of the ring species scenario, an explicit biogeographical model was proposed to account for the occurrence of intraspecific sympatry between two subspecies in southern California (the 'southern closure' model). Here we develop an alternative ring species model that is informed by the geomorphological development of the California Coast Ranges, and which situates the point of ring closure in the Monterey Bay region of central coastal California (the 'Monterey closure' model). Our study has two aims. The first is to use phylogenetic methods to evaluate the two competing biogeographical models. The second is to describe patterns of phylogeographical diversity throughout the range of the Ensatina complex, and to compare these patterns with previously published molecular systematic data. Western North America, with a focus on the state of California, USA. We obtained mitochondrial DNA sequence data from 385 individuals from 224 populations. A phylogeny was inferred using Bayesian techniques, and the geographical distributions of haplotypes and clades were mapped. The two biogeographical ring species models were tested against our Bayesian topology, including the associated Bayesian 95% credible set of trees. High levels of phylogeographical diversity were revealed, especially in central coastal and northern California. Our Bayesian topology contradicts the Monterey closure model; however, 0.08% of the trees in our Bayesian 95% credible set are consistent with this model. In contrast, the classic ring species biogeographical model (the southern closure model) is consistent with our Bayesian topology, as were 99.92% of the trees in our 95% credible set. Our Bayesian phylogenetic analysis most strongly supports the classic ring species model, modified to accommodate an improved understanding of the complex geomorphological evolution of the California Coast Ranges. In addition, high levels of phylogeographical diversity in central and northern California were identified, which is consistent with the striking levels of allozymic differentiation reported previously from those regions.
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| 4. |
- Kuchta, Shawn, et al.
(författare)
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Pronounced phylogeographic structure on a small spatial scale: Geomorphological evolution and lineage history in the salamander ring species Ensatina eschscholtzii in central coastal California
- 2009
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Ingår i: Molecular Phylogenetics and Evolution. - : Elsevier BV. - 1095-9513 .- 1055-7903. ; 50:2, s. 240-255
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Tidskriftsartikel (refereegranskat)abstract
- The salamander Ensatina eschscholtzii is a classic example of a ring species, and has an intricate biogeographic history. Within a part of the ring distribution, earlier work using allozymes disclosed high levels of genetic structure in central coastal California, where the subspecies oregonensis, xanthoptica, and eschscholtzii meet. We used mitochondrial cytochrome b sequences to further examine patterns of divergence in this area, including data from 155 localities (309 individuals). Our focus is on the documentation of population-level haplotype lineages. We show that oregonensis is represented by two unrelated, phenotypically similar clades, both of which possess substantial substructure of their own. The subspecies xanthoptica includes two lineages that differ in phenotype, one of which has colonized the foothills of the Sierra Nevada. The subspecies eschscholtzii occurs mainly to the south, but some populations from a northern lineage extend into the Monterey Bay region, where they approach xanthoptica geographically. In sum, populations in the central coastal California region form a distributional patchwork, including three subspecies, three clades (which differ from the three subspecies), and ten haplotype lineages. We conclude that such striking levels of phylogeographic structure reflect interspersed episodes of spatial fragmentation, in part driven by the complex geomorphological evolution of the California Coast Range system. (C) 2008 Elsevier Inc. All rights reserved.
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