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Little Genetic Variation (little + genetic_variation)
Selected AbstractsInsights from comparative analyses of aging in birds and mammalsAGING CELL, Issue 2 2010Robert E. Ricklefs Summary Many laboratory models used in aging research are inappropriate for understanding senescence in mammals, including humans, because of fundamental differences in life history, maintenance in artificial environments, and selection for early aging and high reproductive rate. Comparative studies of senescence in birds and mammals reveal a broad range in rates of aging among a variety of taxa with similar physiology and patterns of development. These comparisons suggest that senescence is a shared property of all vertebrates with determinate growth, that the rate of senescence has been modified by evolution in response to the potential life span allowed by extrinsic mortality factors, and that most variation among species in the rate of senescence is independent of commonly ascribed causes of aging, such as oxidative damage. Individuals of potentially long-lived species, particularly birds, appear to maintain high condition to near the end of life. Because most individuals in natural populations of such species die of aging-related causes, these populations likely harbor little genetic variation for mechanisms that could extend life further, or these mechanisms are very costly. This, and the apparent evolutionary conservatism in the rate of increase in mortality with age, suggests that variation in the rate of senescence reflects fundamental changes in organism structure, likely associated with the rate of development, rather than physiological or biochemical processes influenced by a few genes. Understanding these evolved differences between long-lived and short-lived organisms would seem to be an essential foundation for designing therapeutic interventions with respect to human aging and longevity. [source] 120 Exploration of Morphological Variation Within the Genus Pediastrum Meyen 1829 (Chlorophyceae, Chlorophyta)JOURNAL OF PHYCOLOGY, Issue 2003H. A. McManus Monographic works on the green algal genus, Pediastrum Meyen 1829 (Chlorophyceae, Chlorophyta), have described species, varieties and forms based on such characteristics as the size and shape of the marginal cells, pattern of cell wall sculpturing and extent of cell wall sculpturing. Depending on the author, the number of taxa assigned to the genus Pediastrum varies. Due to the lack of quantitative value to these characteristics, it has been difficult for other researchers to assign appropriate taxonomy to wild isolates. A molecular phylogeny including multiple strains from both culture collections and wild samples confirms relationships found by previous molecular studies on fewer taxa, in which the family Hydrodictyaceae forms a monophyletic group within the Sphaeropleales, and that the genera Hydrodictyon and Sorastrum are derived from Pediastrum. Hydrodicyton forms a monophyletic clade and consists of three species, H. reticulatum, H. africanum, and H. patenaeforme. Multiple isolates of H. reticulatum reveal little genetic variation between different geographic localities. Inclusion of wild isolates permits a more thorough exploration of morphological variation within the genus Pediastrum, and what characters may be taxonomically informative, particularly in the species P. boryanum and P. duplex. Wild isolates sampled from different areas also offers information regarding geographic variation and potential morphological convergence. [source] A Signal for Independent Coastal and Continental histories among North American wolvesMOLECULAR ECOLOGY, Issue 4 2005BYRON V. WECKWORTH Abstract Relatively little genetic variation has been uncovered in surveys across North American wolf populations. Pacific Northwest coastal wolves, in particular, have never been analysed. With an emphasis on coastal Alaska wolf populations, variation at 11 microsatellite loci was assessed. Coastal wolf populations were distinctive from continental wolves and high levels of diversity were found within this isolated and relatively small geographical region. Significant genetic structure within southeast Alaska relative to other populations in the Pacific Northwest, and lack of significant correlation between genetic and geographical distances suggest that differentiation of southeast Alaska wolves may be caused by barriers to gene flow, rather than isolation by distance. Morphological research also suggests that coastal wolves differ from continental populations. A series of studies of other mammals in the region also has uncovered distinctive evolutionary histories and high levels of endemism along the Pacific coast. Divergence of these coastal wolves is consistent with the unique phylogeographical history of the biota of this region and re-emphasizes the need for continued exploration of this biota to lay a framework for thoughtful management of southeast Alaska. [source] Phylogeographic analysis of a recent radiation of Enallagma damselflies (Odonata: Coenagrionidae)MOLECULAR ECOLOGY, Issue 10 2002J. Turgeon Abstract A phylogenetic hypothesis revealed two recent radiations among species of Enallagma damselflies, and extensive ecological work suggests that both adaptive and nonadaptive processes are involved in these radiations. We analysed the geographical pattern of genetic variability at 868 bp of mitochondrial DNA (mtDNA) among 283 individuals of 5 species displaying little ecological differentiation to identify the ancestral lineage, support their independent evolutionary trajectories and identify historical events and the underlying mechanism for one of these radiations. Nested clade analysis results clearly support a past event of range fragmentation in E. hageni. These Atlantic and Continental hageni races experienced distinct dispersal histories and still maintain nearly nonoverlapping ranges All four other species derive from the Continental hageni. Whereas three species endemic to the Atlantic coastal plain show little genetic variation, E. ebrium shared several haplotypes with the Continental hageni. Contrasting levels of genetic differentiation between E. hageni and E. ebrium in geographical areas associated with distinct events of E. hageni's recent history support the recent origin of this species. Altogether, our results are compatible with a process of radiation via divergence in mate recognition systems within the Continental hageni race following secondary contacts between putative refugial races. [source] Identification of RAPD markers linked to recessive genes conferring siliqua shatter resistance in Brassica rapaPLANT BREEDING, Issue 6 2003O. Mongkolporn Abstract Shattering of siliquae causes significant seed loss in canola (Brassica napus) production worldwide. There is little genetic variation for resistance to shatter in canola and, hence, the trait has been studied in B. rapa. Previous studies have shown two randomly segregating recessive genes to be responsible for shatter resistance. Three random amplified polymorphic DNA markers were identified as being linked to shatter resistance using bulked segregant analysis in a F3B. rapa population. The population was derived from a cross between a shatter-susceptible Canadian cultivar and a shatter-resistant Indian line. Of the three markers, RAC-3900 and RX-71000 were linked to recessive sh1 and sh2 alleles, and SAC-201300 was linked to both dominant Sh1 and Sh2 alleles. The common marker for the dominant wild-type allele for the two loci was explained to have resulted from duplication of an original locus and the associated markers through chromosome duplication and rearrangements in the process of evolution of the modern B. rapa from its progenitor that had a lower number of chromosomes. Segregation data from double heterozygous F3 families, although limited, indicated the markers were not linked to each other and provided further evidence for the duplication hypothesis. [source] | ||||||||||