Main Lineages (main + lineage)

Distribution by Scientific Domains


Selected Abstracts


Phylogeny and biogeography of Yellow-headed and Blue-fronted Parrots (Amazona ochrocephala and Amazona aestiva) with special reference to the South American taxa

IBIS, Issue 3 2007
CAMILA C. RIBAS
The Yellow-headed Parrot (Amazona ochrocephala) has a broad Neotropical distribution, ranging from Mexico to the Amazon Basin, and a history of complex taxonomy and controversial species limits. Recent molecular analyses have started to clarify the taxonomic arrangement of the complex, but have not included a representative geographical sampling from South America. These studies have shown that the Yellow-headed complex can be divided into three main lineages, and seems to be paraphyletic, due to the inclusion of the Blue-fronted Parrot (Amazona aestiva) that occurs in central South America. Here we present a phylogenetic analysis based on mitochondrial DNA sequences of 45 representatives of the Yellow-headed complex from South and Central America, plus 13 Blue-fronted individuals from different localities in South America. Our analyses recover the three primary lineages found previously in the Yellow-headed complex, show that there is genetic structure in the South American lineage, which can be divided into two well-supported, closely related clades, and demonstrate that Blue-fronted samples are distributed in both clades. Differentiation of South American Blue-fronted and Yellow-headed Parrot populations does not correspond to the plumage differences used to distinguish the Blue-fronted Parrot from the Yellow-headed Parrot, nor to plumage differences used to distinguish among South American Yellow-headed subspecies. This suggests that traditional taxonomy based on plumage characters needs revision, and that this may be an interesting example of ongoing divergence-with-gene-flow related to the forest/open area ecotone in southern Amazonia. [source]


Development and selection of ,, T cells

IMMUNOLOGICAL REVIEWS, Issue 1 2007
Na Xiong
Summary:, Two main lineages of T cells develop in the thymus: those that express the ,, T-cell receptor (TCR) and those that express the ,, TCR. Whereas the development, selection, and peripheral localization of newly differentiated ,, T cells are understood in some detail, these processes are less well characterized in ,, T cells. This review describes research carried out in this laboratory and others, which addresses several key aspects of ,, T-cell development, including the decision of precursor cells to differentiate into the ,, versus ,, lineage, the ordered differentiation over the course of ontogeny of functional ,, T-cell subsets expressing distinct TCR structures, programming of ordered V, gene rearrangement in the thymus, including a molecular switch that ensures appropriate V, rearrangements at the appropriate stage of development, positive selection in the thymus of ,, T cells destined for the epidermis, and the acquisition by developing ,, T cells of cues that determine their correct localization in the periphery. This research suggests a coordination of molecularly programmed events and cellular selection, which enables specialization of the thymus for production of distinct T-cell subsets at different stages of development. [source]


Impact of ice ages on circumpolar molecular diversity: insights from an ecological key species

MOLECULAR ECOLOGY, Issue 9 2005
I. G. ALSOS
Abstract We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal ,Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal ,Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The ,Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions. [source]


Fine-scale phylogeographical analysis of Mediterranean Anacamptis palustris (Orchidaceae) populations based on chloroplast minisatellite and microsatellite variation

MOLECULAR ECOLOGY, Issue 10 2003
S. Cozzolino
Abstract The phylogeographical history of the rare marsh orchid Anacamptis palustris (Orchidaceae) was reconstructed using highly polymorphic chloroplast minisatellite and microsatellite loci. Allelic variation at chloroplast microsatellite loci was due to length variation in poly(A/T) repeats and was informative on a regional scale, but was not sufficient to unravel relationships among populations on a local geographical scale. The minisatellite locus, however, was found to be highly variable. Nine distinct repeat types were found and variation in repeat number occurred in five repeat types. The distribution of chloroplast haplotypes, combining microsatellite and minisatellite repeat type variation, provided a clear phylogeographical picture on a large geographical scale, whereas length variation in one highly polymorphic minisatellite repeat type provided fine-scale phylogeographical information. Mediterranean populations could be divided into four main lineages, a western European lineage, a northern and central Italian lineage, a well-isolated southern Italian (Apulian) lineage, and an eastern European lineage. Variation at the most variable minisatellite repeat type N revealed 19 alleles and allowed the study of seed-mediated gene flow and an estimation of the ratio of pollen to seed flow among neighbouring populations. [source]


Mitochondrial cytochrome b sequence yields new insight into the speciation of social voles in south-west Asia

BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 1 2009
BORIS KRY, TUFEK
We established a cytochrome b (cyt b) phylogeny for six species of social voles. A Bayesian approach to phylogenetic reconstruction (BI) and a maximum likelihood (ML) tree revealed a dichotomy into two major clusters, namely a Microtus guentheri cluster and a M. socialis cluster. The three main lineages that emerged within each of these two clusters were separated by the K2P divergences which are above the intraspecific variation in Microtus. All six species were also retrieved in the minimum spanning network. Within its present taxonomic scope, M. guentheri is paraphyletic and consists of two allopatric sibling species: M. guentheri (Syria, Israel) and M. hartingi (Anatolia and the Balkans). The closest relative to these two species is M. dogramacii, which is possibly a sister species to M. hartingi. The two geographic samples were identified as M. irani, one from Shiraz (Iran) and the other from Balkusan (Turkey). The cyt b sequence confirmed the specific status of M. anatolicus within the M. socialis cluster. Although five species of social voles occur within a radius of < 500 km in the north-eastern corner of the Mediterranean, small-scale sympatry is exceptional. Species richness in this region possibly originates from past fragmentation with subsequent allopatric speciation in refugial areas. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 121,128. [source]