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Length Variation (length + variation)
Selected AbstractsMitochondrial DNA differentiation between two forms of trout Salmo letnica, endemic to the Balkan Lake Ohrid, reflects their reproductive isolationMOLECULAR ECOLOGY, Issue 12 2004J. SELL Abstract Mitochondrial haplotype diversity in sympatric populations of Ohrid trout, Salmo letnica was investigated by polymerase chain reaction,restriction fragment length polymorphism (PCR-RFLP) analysis of the mtDNA control region and ND1, ND3/4, ND5/6 segments. A 310 bp fragment at the 5, end, and a 340,572 bp fragment at the 3, end of the control region were sequenced from representatives of the populations studied. Based on pairwise comparison of the sequences, five new haplotypes were identified plus one identical with the brown trout Andalusian haplotype from the southern Iberian Peninsula. The combination of both RFLP and sequence data sets yielded a total of 10 composite haplotypes. A high degree of genetic subdivision between S. letnica typicus and S. letnica aestivalis populations was observed. The notion of a sympatric origin for the two morphs is discussed. Length variation of the mtDNA control region due to the presence of an 82 bp unit, tandemly repeated one to four times, in the region between the conserved sequence block-3 (CSB-3) and the gene for phenylalanine tRNA is reported. Further, we demonstrate that a single duplication of the approximately 82 bp repeat unit is a common element of the salmonid mitochondrial control region. The unique genetic structure of Ohrid trout represents a highly valuable genetic resource that deserves appropriate management and conservation. [source] Sperm competition and maternal effects differentially influence testis and sperm size in Callosobruchus maculatusJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 5 2009L. GAY Abstract The evolutionary factors affecting testis size are well documented, with sperm competition being of major importance. However, the factors affecting sperm length are not well understood; there are no clear theoretical predictions and the empirical evidence is inconsistent. Recently, maternal effects have been implicated in sperm length variation, a finding that may offer insights into its evolution. We investigated potential proximate and microevolutionary factors influencing testis and sperm size in the bruchid beetle Callosobruchus maculatus using a combined approach of an artificial evolution experiment over 90 generations and an environmental effects study. We found that while polyandry seems to select for larger testes, it had no detectable effect on sperm length. Furthermore, population density, a proximate indicator of sperm competition risk, was not significantly associated with sperm length or testis size variation. However, there were strong maternal effects influencing sperm length. [source] The inheritance of heteroplasmy in guppiesJOURNAL OF FISH BIOLOGY, Issue 5 2002J. S. Taylor Guppies Poecilia reticulata from the Rio Grande, Trinidad are heteroplasmic; individuals possess up to nine different-sized mtDNA haplotypes. A PCR survey of mtDNA length variation that included mothers and embryos suggests that a large number of mitochondrial genomes (possibly within a much smaller number of organelles) pass from one generation to the next. [source] Fine-scale phylogeographical analysis of Mediterranean Anacamptis palustris (Orchidaceae) populations based on chloroplast minisatellite and microsatellite variationMOLECULAR ECOLOGY, Issue 10 2003S. 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] Population genetics of shortnose sturgeon Acipenser brevirostrum based on mitochondrial DNA control region sequencesMOLECULAR ECOLOGY, Issue 10 2002C. Grunwald Abstract Shortnose sturgeon is an anadromous North American acipenserid that since 1973 has been designated as federally endangered in US waters. Historically, shortnose sturgeon occurred in as many as 19 rivers from the St. John River, NB, to the St. Johns River, FL, and these populations ranged in census size from 101 to 104, but little is known of their population structure or levels of gene flow. We used the polymerase chain reaction (PCR) and direct sequence analysis of a 440 bp portion of the mitochondrial DNA (mtDNA) control region to address these issues and to compare haplotype diversity with population size. Twenty-nine mtDNA nucleotide-substitution haplotypes were revealed among 275 specimens from 11 rivers and estuaries. Additionally, mtDNA length variation (6 haplotypes) and heteroplasmy (2,5 haplotypes for some individuals) were found. Significant genetic differentiation (P < 0.05) of mtDNA nucleotide-substitution haplotypes and length-variant haplotypes was observed among populations from all rivers and estuaries surveyed with the exception of the Delaware River and Chesapeake Bay collections. Significant haplotype differentiation was even observed between samples from two rivers (Kennebec and Androscoggin) within the Kennebec River drainage. The absence of haplotype frequency differences between samples from the Delaware River and Chesapeake Bay reflects a probable current absence of spawning within the Chesapeake Bay system and immigration of fish from the adjoining Delaware River. Haplotypic diversity indices ranged between 0.817 and 0.641; no relationship (P > 0.05) was found between haplotype diversity and census size. Gene flow estimates among populations were often low (< 2.0), but were generally higher at the latitudinal extremes of their distribution. A moderate level of haplotype diversity and a high percentage (37.9%) of haplotypes unique to the northern, once-glaciated region suggests that northern populations survived the Pleistocene in a northern refugium. Analysis of molecular variance best supported a five-region hierarchical grouping of populations, but our results indicate that in almost all cases populations of shortnose sturgeon should be managed as separate units. [source] A geochronological approach to understanding the role of solar activity on Holocene glacier length variability in the Swiss AlpsGEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2006Anne Hormes ABSTRACT. We present a radiocarbon data set of 71 samples of wood and peat material that melted out or sheared out from underneath eight presentday mid-latitude glaciers in the Central Swiss Alps. Results indicated that in the past several glaciers have been repeatedly less extensive than they were in the 1990s. The periods when glaciers had a smaller volume and shorter length persisted between 320 and 2500 years. This data set provides greater insight into glacier variability than previously possible, especially for the early and middle Holocene. The radiocarbon-dated periods defined with less extensive glaciers coincide with periods of reduced radio-production, pointing to a connection between solar activity and glacier melting processes. Measured long-term series of glacier length variations show significant correlation with the total solar irradiance. Incoming solar irradiance and changing albedo can account for a direct forcing of the glacier mass balances. Long-term investigations of atmospheric processes that are in interaction with changing solar activity are needed in order to understand the feedback mechanisms with glacier mass balances. [source] Modified methodology for computing interference in LEO satellite environmentsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 6 2003Raúl Chávez Santiago Abstract Computing interference is very important in satellite networks design in order to assure the electromagnetic compatibility (EMC) with other radiocommunication systems. There are different methods to compute interference in geostationary (GEO) satellite systems including conventional methods using link budget equations and alternate methods such as increase in noise temperature. However, computing interference in low earth orbit (LEO) systems represents a different problem. Due to the special characteristics of this kind of orbits, the elevation angle at any site changes continuously over time, meaning a time dependent change of the propagation path length between an interfering transmitter and an interfered-with receiver, and of the discrimination provided by the transmitting and/or the receiving antenna. Thus, conventional interference prediction methods developed for fixed links must be adapted to the case of LEO systems. To overcome this problem a mathematical model that characterizes the path length variations by an average value obtained from the probability density function of the varying distance between an interfering transmitter and an interfered- with receiver is proposed in this paper. This average path length enables the use of conventional link budget methods to reduce the computation time for the evaluation of interference in LEO satellite environments. Two practical examples show the possible applications of the proposed model. Copyright © 2003 John Wiley & Sons, Ltd. [source] Empirical preprocessing methods and their impact on NIR calibrations: a simulation studyJOURNAL OF CHEMOMETRICS, Issue 2 2005S. N. Thennadil Abstract The extraction of chemical information from dense particulate suspensions, such as industrial slurries and biological suspensions, using near-infrared (NIR) spectroscopic measurements is complicated by sample-to-sample path length variations due to light scattering. Empirical preprocessing techniques such as multiplicative scatter correction (MSC), extended MSC and derivatives have been applied to remove these effects and in some cases have shown promise. While the performance of these techniques and other related approaches is known to depend on the nature and extent of the variations and on the measurement configuration, detailed investigations into the efficacy of these approaches under various conditions have not been previously undertaken. The main obstacle to carrying out such investigations has been the lack of, and the difficulty in obtaining, an accurate and comprehensive experimental data set. In this work, simulations that generate ,actual' measurements were carried out to obtain ,experimental' spectroscopic data on particulate systems. This was achieved by solving the exact transport equation for light propagation. A model system comprising four chemical components with one consisting of spherical submicron particles was considered. Total diffuse transmittance and reflectance data generated through simulations for moderate particle concentrations were used as the basis for examining the effect of particle size variations and measurement configurations on the efficacy of a number of preprocessing techniques in enhancing the performance of partial least squares (PLS) models for predicting the concentration of one of the non-scattering chemical species. Additionally, a form of extended multiplicative signal correction based on considerations arising from fundamental light scattering theory is proposed and found to perform better than the other techniques for the cases considered in the study. Copyright © 2005 John Wiley & Sons, Ltd. [source] | ||||||||||