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Within-population Diversity (within-population + diversity)
Selected AbstractsPopulations do not become less genetically diverse or more differentiated towards the northern limit of the geographical range in clonal Vaccinium stamineum (Ericaceae)NEW PHYTOLOGIST, Issue 2 2008Sarah B. Yakimowski Summary ,,Geographically peripheral populations are expected to exhibit lower genetic diversity and higher differentiation than central populations because of their smaller size and greater spatial isolation. In plants, a shift from sexual to clonal asexual reproduction may further reduce diversity and increase differentiation. ,,Here, these predictions were tested by assaying 36 inter-simple sequence repeat (ISSR) polymorphisms in 21 populations of the woody, clonal plant Vaccinium stamineum in eastern North America, from the range center to its northern limit where it has ,threatened' status. Populations decline in frequency, but not size or sexual reproductive output, across the range. ,,Within-population diversity did not decline towards range margins. Modest genetic differentiation among populations increased slightly towards range margins and in small populations with high clonal propagation and low seed production, although none of these trends was significant. Low seed production and high clonal propagation were not associated with large-scale clonal spread. ,,By combining demographic and genetic data, this study determined that increased population isolation, rather than reduced population size, can account for the weak increase in genetic differentiation at range margins. [source] Population Genetic Structure of the Medicinal Plant Vitex rotundifolia in China: Implications for its Use and ConservationJOURNAL OF INTEGRATIVE PLANT BIOLOGY, Issue 9 2008Yuan Hu Abstract Vitex rotundifolia L. is an important plant species used in traditional Chinese medicine. For its efficient use and conservation, genetic diversity and clonal variation of V. rotundifolia populations in China were investigated using inter-simple sequence repeat markers. Fourteen natural populations were included to estimate genetic diversity, and a large population with 135 individuals was used to analyze clonal variation and fine-scale spatial genetic structure. The overall genetic diversity (GD) of V. rotundifolia populations in China was moderate (GD = 0.190), with about 40% within-population variation. Across all populations surveyed, the average within-population diversity was moderate (P = 22.6%; GD = 0.086). A relatively high genetic differentiation (Gst = 0.587) among populations was detected based on the analysis of molecular variance data. Such characteristics of V. rotundifolia are likely attributed to its sexual/asexual reproduction and limited gene flow. The genotypic diversity (D = 0.992) was greater than the average values of a clonal plant, indicating its significant reproduction through seedlings. Spatial autocorrelation analysis showed a clear within-population structure with gene clusters of approximately 20 m. Genetic diversity patterns of V. rotundifolia in China provide a useful guide for its efficient use and conservation by selecting particular populations displaying greater variation that may contain required medicinal compounds, and by sampling individuals in a population at >20 m spatial intervals to avoid collecting individuals with identical or similar genotypes. [source] Nuclear and chloroplast microsatellites reveal extreme population differentiation and limited gene flow in the Aegean endemic Brassica cretica (Brassicaceae)MOLECULAR ECOLOGY, Issue 23 2007KRISTINA EDH Abstract Nuclear and chloroplast microsatellite markers were used to study population structure and gene flow among seven Cretan populations of the Aegean endemic plant species Brassica cretica (Brassicaceae). Both nuclear and chloroplast markers revealed exceptionally high levels of population differentiation (overall FST = 0.628 and 1.000, respectively) and relatively little within-population diversity (overall HS = 0.211 and 0.000, respectively). Maximum-likelihood estimates of directional migration rates were low among all pairs of populations (average Nm = 0.286). There was no evidence that differences in flower colour between populations had any influence on historical levels of gene flow. In addition, a haplotype network showed that all five chloroplast haplotypes found in the sample were closely related. Together, these results suggest that current patterns of diversification in B. cretica are mainly a result of genetic drift during the last half million years. The main conclusions from the present study are consistent with the prevailing hypothesis that plant diversification in the Aegean region is driven by random rather than adaptive differentiation among isolated populations. [source] Long-term population isolation in the endangered tropical tree species Caesalpinia echinata Lam. revealed by chloroplast microsatellitesMOLECULAR ECOLOGY, Issue 12 2003C. F. Lira Abstract Habitat fragmentation represents the single most serious threat to the survival of tropical ecosystems. In formulating strategies to counteract the detrimental effects of fragmentation, knowledge of the levels and patterns of genetic diversity within and between natural populations is vital to the establishment of any conservation programme. We utilized polymorphic chloroplast microsatellite markers to analyse genetic diversity in populations of the endangered tropical tree Caesalpinia echinata Lam. representing the entire extant range of the species. Levels of within-population diversity were low, with only two of seven populations studied displaying any variation. The vast majority of the genetic variation was partitioned between geographical regions (36%) and between populations within regions (55%). These levels of genetic structuring, coupled with a calculated pollen-to-seed flow ratio of , 6.7:1, suggest that there has been little gene flow between the three major geographical regions over an extended period. Thus, the current tripartite distribution of the species is more consistent with the existence of separate glacial refugia, rather than reflecting any anthropogenic effects. [source] Sampling within the genome for measuring within-population diversity: trade-offs between markersMOLECULAR ECOLOGY, Issue 7 2002S. Mariette Abstract Experimental results of diversity estimates in a set of populations often exhibit contradictory patterns when different marker systems are used. Using simulations we identified potential causes for these discrepancies. These investigations aimed also to detect whether different sampling strategies of markers within the genome resulted in different estimates of the diversity at the whole genome level. The simulations consisted in generating a set of populations undergoing various evolutionary scenarios which differed by population size, migration rate and heterogeneity of gene flow. Population diversity was then computed for the whole genome and for subsets of loci corresponding to different marker techniques. Rank correlation between the two measures of diversity were investigated under different scenarios. We showed that the heterogeneity of genetic diversity either between loci (genomic heterogeneity, GH) or among populations (population heterogeneity, PH) varied greatly according to the evolutionary scenario considered. Furthermore, GH and PH were major determinants of the level of rank correlation between estimates of genetic diversities obtained using different kinds of markers. We found a strong positive relationship between the level of the correlation and PH, whatever the marker system. It was also shown that, when GH values were constantly low during generations, a reduced number of microsatellites was enough to predict the diversity of the whole genome, whereas when GH increased, more loci were needed to predict the diversity and amplified fragment length polymorphism markers would be more recommended in this case. Finally the results are discussed to recommend strategies for gene diversity surveys. [source] Microsatellite diversity and genetic structure of fragmented populations of the rare, fire-dependent shrub Grevillea macleayanaMOLECULAR ECOLOGY, Issue 6 2002Phillip R. England Abstract Recent habitat loss and fragmentation superimposed upon ancient patterns of population subdivision are likely to have produced low levels of neutral genetic diversity and marked genetic structure in many plant species. The genetic effects of habitat fragmentation may be most pronounced in species that form small populations, are fully self-compatible and have limited seed dispersal. However, long-lived seed banks, mobile pollinators and long adult lifespans may prevent or delay the accumulation of genetic effects. We studied a rare Australian shrub species, Grevillea macleayana (Proteaceae), that occurs in many small populations, is self-compatible and has restricted seed dispersal. However, it has a relatively long adult lifespan (c. 30 years), a long-lived seed bank that germinates after fire and is pollinated by birds that are numerous and highly mobile. These latter characteristics raise the possibility that populations in the past may have been effectively large and genetically homogeneous. Using six microsatellites, we found that G. macleayana may have relatively low within-population diversity (3.2,4.2 alleles/locus; Hexp= 0.420,0.530), significant population differentiation and moderate genetic structure (FST = 0.218) showing isolation by distance, consistent with historically low gene flow. The frequency distribution of allele sizes suggest that this geographical differentiation is being driven by mutation. We found a lack mutation-drift equilibrium in some populations that is indicative of population bottlenecks. Combined with evidence for large spatiotemporal variation of selfing rates, this suggests that fluctuating population sizes characterize the demography in this species, promoting genetic drift. We argue that natural patterns of pollen and seed dispersal, coupled with the patchy, fire-shaped distribution, may have restricted long-distance gene flow in the past. [source] | ||||||||||