Morphological and microsatellite diversity associated with ecological factors in natural populations of Medicago laciniata Mill. (Fabaceae)

Environmental gradients shape the genetic structure of two medicinal Salvia species in Jordan

Environmental gradients, and particularly climatic variables, exert a strong influence on plant distribution and, potentially, population genetic diversity and differentiation. Differences in water availability can cause among-population variation in ecological processes and can thus interrupt populations' connectivity and isolate them environmentally. The present study examines the effect of environmental heterogeneity on plant populations due to environmental isolation unrelated to geographic distance. Using AFLP markers, we analyzed genetic diversity and differentiation among 12 Salvia spinosa populations and 13 Salvia syriaca populations from three phytogeographical regions (Mediterranean, Irano-Turanian and Saharo-Arabian) representing the extent of the species' geographic range in Jordan. Differences in geographic location and climate were considered in the analyses. For both species, flowering phenology varied among populations and regions. Irano-Turanian and Saharo-Arabian populations had higher genetic diversity than Mediterranean populations, and genetic diversity increased significantly with increasing temperature. Genetic diversity in Salvia syriaca was affected by population size, while genetic diversity responded to drought in S. spinosa. For both species, high levels of genetic differentiation were found as well as two well-supported phytogeographical groups of populations, with Mediterranean populations clustering in one group and the Irano-Turanian and Saharo-Arabian populations in another. Genetic distance was significantly correlated to environmental distance, but not to geographic distance. Our data indicate that populations from moist vs. arid environments are environmentally isolated, where environmental gradients affect their flowering phenology, limit gene flow and shape their genetic structure. We conclude that environmental heterogeneity may act as driver for the observed variation in genetic diversity.

Trace element contamination differentiates the natural population of Scots pine: evidence from DNA microsatellites and needle morphology

The Scots pine is often used in the biomonitoring of forests. Studies on the chemical composition plus variability of its needles morphological structure allow for an assessment of the state of environmental pollution. However, in their natural populations, the response of individual trees to stress differs. This study reports on the influence of long-term soil contamination with trace elements on the morphology of the needles, its possible relation to the differentiation of the genetic pool, and their implications for biomonitoring. In the natural and self-renewable pine stand growing near the point polluter (zinc smelter, Upper Silesia, Poland), two categories of trees are observed with respect to their health status: pollution-tolerant (T) and pollution-sensitive (S). A detailed analysis of the trace element content of the needles reveals that the concentration of Cd, Zn, Pb, and Cu in the needles is significantly higher in S as compared to T individuals. The metal accumulation pattern decidedly follows the sequence Pb > Cd > Cu > Zn. An analysis of the fluctuating asymmetry (FA) of the needles reveals that sensitive trees showed an FA index ten times higher in comparison to tolerant ones. Moreover, the high differences between these S and T tree groups are also observed in the basic genetic diversity parameters investigated by an analysis of DNA simple sequence repeats (SSR). The concentration of trace elements in pine needles, distinct in sensitive and tolerant trees and in connection with their morphological and genetic characteristics, may reflect an adaptation process. The level of Mg and Fe content in the needles could be a physiological-toxicological index for evaluating trace element "lethality" expressed as Mg and Fe mineral-survival strategies. The example of differences described in this Scots pine population should be taken into consideration in ecotoxicological research to better interpret the obtained results.

Large-scale adaptive divergence in Boechera fecunda, an endangered wild relative of Arabidopsis

Many biological species are threatened with extinction because of a number of factors such as climate change and habitat loss, and their preservation depends on an accurate understanding of the extent of their genetic variability within and among populations. In this study, we assessed the genetic divergence of five quantitative traits in 10 populations of an endangered cruciferous species, Boechera fecunda, found in only several populations in each of two geographic regions (WEST and EAST) in southwestern Montana. We analyzed variation in quantitative traits, neutral molecular markers, and environmental factors and provided evidence that despite the restricted geographical distribution of this species, it exhibits a high level of genetic variation and regional adaptation. Conservation efforts therefore should be directed to the preservation of populations in each of these two regions without attempting transplantation between regions. Heritabilities and genetic coefficients of variation estimated from nested ANOVAs were generally high for leaf and rosette traits, although lower (and not significantly different from 0) for water-use efficiency. Measures of quantitative genetic differentiation, Q_ST, were calculated for each trait from each pair of populations. For three of the five traits, these values were significantly higher between regions compared with those within regions (after adjustment for neutral genetic variation, F_ST). This suggested that natural selection has played an important role in producing regional divergence in this species. Our analysis also revealed that the B. fecunda populations appear to be locally adapted due, at least in part, to differences in environmental conditions in the EAST and WEST regions.

Genome diversity in wild grasses under environmental stress

Patterns of diversity distribution in the Isa defense locus in wild-barley populations suggest adaptive selection at this locus. The extent to which environmental selection may act at additional nuclear-encoded defense loci and within the whole chloroplast genome has now been examined by analyses in two grass species. Analysis of genetic diversity in wild barley (Hordeum spontaneum) defense genes revealed much greater variation in biotic stress-related genes than abiotic stress-related genes. Genetic diversity at the Isa defense locus in wild populations of weeping ricegrass [Microlaena stipoides (Labill.) R. Br.], a very distant wild-rice relative, was more diverse in samples from relatively hotter and drier environments, a phenomenon that reflects observations in wild barley populations. Whole-chloroplast genome sequences of bulked weeping ricegrass individuals sourced from contrasting environments showed higher levels of diversity in the drier environment in both coding and noncoding portions of the genome. Increased genetic diversity may be important in allowing plant populations to adapt to greater environmental variation in warmer and drier climatic conditions.

Macroecological patterns of genetic structure and diversity in the aquatic moss Platyhypnidium riparioides

Genetic diversity and structure are described in the aquatic moss Platyhypnidium riparioides to assess its dispersal ability at a regional scale and to determine whether patterns of genetic differentiation correlate with environmental variation. Variation at six nuclear microsatellite loci from 50 populations in southern Belgium was investigated through Mantel tests, partial Mantel tests and spatial analysis of molecular variance. Overall patterns of genotypic variation showed strong differentiation among populations at a regional scale (F(ST) = 0.57). The high values of F(IS) observed within populations at both the ramet and genet levels, and the higher proportion of ramets with the same genotype than expected by chance, all point to a strongly clonal or selfing mating system. A genetic discontinuity was identified between northern and southern groups of populations. Within each group, F(ST) and geographical distances were significantly correlated. Partial Mantel tests suggest that genetic and ecological distances are significantly correlated in the southern group. The results point to strong dispersal limitation at the landscape scale and suggest that the southern and northern groups experienced different histories. Within the former, the correlation between genetic and ecological variation is suggestive of reproductive isolation among ecotypes.