Levels Of Within-population Variation Research Articles

Ecology, environment and evolutionary history influence genetic structure in five mammal species from the Italian Alps

The identification and evaluation of the ecological and environmental factors shaping patterns of natural genetic variation are fundamental goals of population and conservation genetics. Many studies focus on factors affecting single species, but it is also important to test whether some influential biotic and abiotic factors are common drivers of genetic diversity across species, or if species or species groups are each affected by different forces; a multi-species analysis is necessary for this. Here we analysed the molecular variation from five mammal species (roe deer, red deer, chamois, mountain hare and European brown hare) at mtDNA and microsatellite loci from the eastern Italian Alps. We use phylogeographical and landscape-level analyses to test the relative influence of large-scale geographical history and contemporary environmental characteristics of the landscape on genetic diversity and differentiation. We found: (1) all study species except brown hare are strongly differentiated into two main groups, located west and east of a major river valley; (2) significant correlations between levels of within-population diversity at both mtDNA and microsatellite loci, and several landscape features such as alpine grassland, water courses and anthropized areas. We conclude that heterogeneous landscape has some influence on within-population diversity, but biogeographical history has probably had the stronger influence on current genetic patterns, despite an apparently large dispersal potential of certain species. However, our results for brown hare show that management actions such as stocking may alter these large-scale patterns.

Microsatellite, blood group and transferrin protein diversity of Estonian dairy cattle breeds

This study investigates genetic diversity within and among three Estonian dairy cattle breeds (Estonian Native, Estonian Red and Estonian Holstein). A total of 36 markers (25 microsatellites, 10 blood group systems and transferrin protein) were investigated and the within-breed diversity was quantified by expected heterozygosity, number of private alleles and mean allelic richness. The population structure was studied by computing the inbreeding coefficients, breed differentiation and relationships were investigated with random drift-based measures and a factorial correspondence analysis. In addition, a neighbour-joining tree was drawn summarising allele sharing distances for 195 individuals of the Estonian breeds, Western Finncattle, and Danish Jersey. The Estonian breeds displayed generally similar levels of within-population diversity. Depending on the set of markers used 6.2 or 4.3% of the total genetic variation can be explained by differences among the breeds. Construction of the tree for individuals revealed a distinctive pattern of grouping for Estonian Holstein, Estonian Red and Danish Jersey, but Estonian Native and Western Finncattle appeared on the same branches. This indicates that the gene pool of Estonian Native largely overlaps with that of Western Finncattle. However, our genetic marker analysis shows that the three Estonian breeds are genetically differentiated, suggesting that the current gene pool of Estonian dairy cattle is diverse.;

Effects of population size and forest management on genetic diversity and structure of the tuberous orchid Orchis mascula

Due to societal changes and altered demands for firewood, the traditional forest management of coppicing has been largely abandoned. As a result, many forest herbs that are specifically adapted to regular opening of the canopy, have suffered significant declines in abundance, and the remaining populations of these species often tend to be small and isolated. Reduced population sizes and pronounced spatial isolation may cause loss of within-population genetic diversity and increased between-population differentiation through random genetic drift and inbreeding. In this study, we investigated genetic diversity and genetic structure of 15 populations of the food-deceptive orchid Orchis mascula using AFLP markers. Within-population genetic diversity significantly increased with increasing population size, indicating genetic impoverishment in small populations. Genetic differentiation, on the other hand, was rather low (ΦST = 0.083) and there was no significant relationship between genetic and geographic distances, suggesting substantial gene flow within the study area. However, strong differences in levels of within-population diversity and among-population differentiation were found for populations located in forests that have been regularly coppiced and populations found in forests that were neglected for more than 50 years and that were totally overgrown by shrubs. Our data thus indicate that a lack of coppicing leads to decreased genetic diversity and increased differentiation in this orchid species, most likely as a result of genetic drift following demographic bottlenecks. From a conservation point of view, this study combined with previous results on the demography of O. mascula in relation to forest management illustrates the importance of coppicing in maintaining viable populations of forest herbs in the long-term.

Genome-wide effects of postglacial colonization in Arabidopsis lyrata

The perennial outcrossing Arabidopsis lyrata is becoming a plant model species for molecular ecology and evolution. However, its evolutionary history, and especially the impact of the climatic oscillations of the Pleistocene on its genetic diversity and population structure, is not well known. We analyzed the broad-scale population structure of the species based on microsatellite variation at 22 loci. A wide sample in Europe revealed that glaciations and postglacial colonization have caused high divergence and high variation in variability between populations. Colonization from Central Europe to Iceland and Scandinavia was associated with a strong decrease of genetic diversity from South to North. On the other hand, the Russian population included in our data set may originate from a different refugium probably located more to the East. These genome-wide patterns must be taken into account in studies aiming at elucidating the genetic basis of local adaptation. As shown by sequence data, most of the loci used in this study do not evolve like typical microsatellite loci and show variable levels of homoplasy: this mode of evolution makes these markers less suitable to investigate the between-continent divergence and more generally the worldwide evolution of the species. Finally, a strong negative correlation was detected between levels of within-population diversity and indices of differentiation such as F(ST). We discuss the causes of this correlation as well as the potential bias it induces on the quantification and interpretation of population structure.

Genetic Variation and Differentiation in Mexican Populations of Common Bush-Tanagers and Chestnut-Capped Brush-Finches

Genetic differentiation among four Mexican populations each of Common Bush-tanagers (Chlorospingus ophthalmicus) and Chestnut-capped Brush-finches (Atlapetes brunneinucha) was evaluated using allozyme electrophoresis. In both species, although levels of within-population variation are moderate, among-population variation is extreme, including fixed differences among populations. Genetic variation is significantly reduced in some populations on the smallest habitat islands. Differentiation is apparently unrelated to geographic distance among populations, and effects of habitat island size and isolation on genetic differentiation are not clear. Populations of the Sierra de los Tuxtlas in Veracruz, however, are strongly differentiated in both species. Resumen. La diferenciación genética entre cuatro poblaciones mexicanas del Saltón Chayotero (Atlapetes brunneinucha) y del Cerquero Verde (Chlorospingus ophthalmicus) fue estudiada usando electroforésis de alozimas. Los niveles de variabilidad intrapoblacional fueron moderados, pero la variabilidad entre poblaciones fue extrema, incluyendo diferencias fijas entre poblaciones, en ambas especies. La variación genética fue reducida significativamente en algunas poblaciones de las islas-habitat más pequeñas. Aparentemente, la diferenciación no está relacionada a la distancia geográfica entre poblaciones, y los efectos de tamaño de la isla-habitat y de aislamiento sobre la diferenciación genética son inciertos. Las poblaciones de la Sierra de Los Tuxtlas, Veracruz, sin embargo, están diferenciadas marcadamente en ambas especies.

Allozyme Variation in Bidens discoidea (Compositae)

Allozyme variation between and within eight populations of the diploid annualBidens discoidea was investigated using gel electrophoresis. The species is relatively homogeneous morphologically in comparison with related species and is highly autogamous. Low levels of within-population variation occur at 16 gene loci, and single alleles are nearly fixed at each of seven loci polymorphic for the species. High levels of differentiation occur between populations, with a mean genetic identity of 0.865. The alleles at the polymorphic loci occur in different combinations in the populations with little apparent geographical pattern. Each population is probably composed of a single lineage of highly homozygous individuals with very limited gene flow between populations.