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Geographic Differentiation (geographic + differentiation)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Evidence for genetic differentiation between the molecular forms M and S within the Forest chromosomal form of Anopheles gambiae in an area of sympatry

INSECT MOLECULAR BIOLOGY, Issue 1 2002
C. Wondji
Abstract We studied genetic variation at ten microsatellite DNA loci in Anopheles gambiae populations from the Forest chromosomal form collected in four villages in Cameroon (Central Africa). Both recently described M and S molecular forms occur in sympatry in this area. Geographic differentiation within form was low (Fst < 0.017) despite geographical distance between collection sites ranging from 35 to 350 km. However, higher (Fst > 0.035) and statistically significant levels of genetic differentiation were observed between forms, being the highest between sympatric M and S populations collected within the same village. Results were consistent across all loci spread throughout the genome, therefore reflecting a genome-wide pattern. Considering previous findings of strong assortative mating within forms and general lack of hybrids in areas of sympatry, we propose that there is now sufficient direct and indirect evidence to consider both M and S molecular forms of An. gambiae as distinct species that have probably speciated recently. [source]

Seamount science scales undersea mountains: new research and outlook

MARINE ECOLOGY, Issue 2010
Thomas A. Schlacher
Abstract Conventional wisdom suggests that seamounts harbour high levels of biodiversity and endemism, play important roles in marine biogeography, are hotspots of biological carbon processing, and support substantial fisheries. However, since fewer than 300 seamounts have been thoroughly sampled, these generalizations remain largely untested. This has provided the motivation for a number of seamount-focused research projects in recent years, including CenSeam, a field project within the Census of Marine Life. This issue presents some of the research output facilitated by CenSeam. Here we summarize the main findings and provide a précis of future research directions highlighted by contributors to the issue. Recent studies show that seamounts can have comparable levels of benthic diversity and endemism to continental margins, but their communities also include a distinct composition of species that can attain higher biomass. Reported geographic differentiation among seamount communities suggests limited larval dispersal, local speciation, geographic isolation, or a combination of these processes. Genetic studies contained in the issue address these themes explicitly, documenting complex patterns of connectivity that depend on spatial scale and life history characteristics. Globally, seamount ecosystems are also under pressure from bottom-contact fishing and ocean acidification. Contributions detailing the footprint of trawling and a risk assessment confirm what has long been suspected: seamount ecosystems are highly vulnerable to disturbance by bottom trawling and recovery from fishing impacts is a lengthy process, likely requiring decades at a minimum. A predicted shallowing of the aragonite saturation horizon caused by ocean acidification is predicted to place deep-water corals at risk, but seamounts may yet provide a spatial/chemical refuge from these impacts. The issue concludes with a ,myth-buster' synthesis that updates the status of the various seamount ecological paradigms. [source]

Genetic structure and random amplified polymorphic DNA diversity of the rapidly declining Angelica palustris (Apiaceae) in Eastern Germany in relation to population size and seed production

PLANT SPECIES BIOLOGY, Issue 3 2005
ANKE DITTBRENNER
Abstract Angelica palustris (Besser) Hoffm. (Apiaceae) is a rare wetland community species that is currently rapidly declining because of changes in land use. In the present study, we analyzed patterns of random amplified polymorphic DNA (RAPD) variation among nine populations of A. palustris in Germany to assess its overall genetic condition. We aimed to examine the level of genetic diversity as well as its local differentiation in relation to population size and geographic distancing between populations. Results achieved from ,ST statistics and amova indicated that most of the variability is distributed among individuals within the populations (57.7%), whereas among-population variation accounted for 30.2% of the variation. Variation between regions was 12.1%. This corresponds to the results of a multivariate analysis based on the asymmetric Soerensen similarity, which also suggested a strong population differentiation, as would be expected from a short-lived species with limited seed dispersal capacities that had never covered extensive areas in Eastern Germany. Consistently the geographic differentiation was not reflected in the RAPD profile. Significant correlations were noted between population size and the percentage of polymorphic loci (P < 0.05) and genetic diversity (P < 0.05). An analysis of seed production showed positive relationships between average seed number and levels of genetic variation. Our results support concerns regarding the loss of genetic diversity in endangered plant populations because this process might have harmful effects on reproductive fitness. [source]

Race and global patterns of phenotypic variation

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 1 2009
John H. Relethford
Abstract Phenotypic traits have been used for centuries for the purpose of racial classification. Developments in quantitative population genetics have allowed global comparison of patterns of phenotypic variation with patterns of variation in classical genetic markers and DNA markers. Human skin color shows a high degree of variation among geographic regions, typical of traits that show extensive natural selection. Even given this high level of geographic differentiation, skin color variation is clinal and is not well described by discrete racial categories. Craniometric traits show a level of among-region differentiation comparable to genetic markers, with high levels of variation within populations as well as a correlation between phenotypic and geographic distance. Craniometric variation is geographically structured, allowing high levels of classification accuracy when comparing crania from different parts of the world. Nonetheless, the boundaries in global variation are not abrupt and do not fit a strict view of the race concept; the number of races and the cutoffs used to define them are arbitrary. The race concept is at best a crude first-order approximation to the geographically structured phenotypic variation in the human species. Am J Phys Anthropol 2009. © 2009 Wiley-Liss, Inc. [source]