Diversity of Nitrogen-Fixing Symbionts of Chamaecrista fasciculata (Partridge Pea) Across Variable Soils

We evaluated whether geographic distance and soil characteristics influence genetic structure of nitrogen-fixing bacterial symbionts associated with the host plant Chamaecrista fasciculata (Partridge Pea). We tested phylogeographic clustering and associations between genetic distance, geographic distance, and soil variables using sequences of 2 bacterial genes and soil chemistry across 23 sites in Mississippi. We identified rhizobia isolated from Partridge Pea as Bradyrhizobium. We detected significant genetic structure at a regional level, and determined that rhizobia within each region were more phylogenetically related than expected. Significant correlation between genetic distance and distances based on soil chemistry suggests environmental influences on rhizobia diversity. High levels of diversity among rhizobia over small spatial scales suggest that symbionts respond to local factors. Understanding geographic diversity in natural assemblages of rhizobia aids in predicting how hosts and symbionts respond to environmental perturbations

Patterns of Genetic Divergence Across Geographically Variable Populations of \u3ci\u3eXanthisma gracile\u3c/i\u3e (Asteraceae)

Premise of research. Numerous biotic and abiotic factors can contribute to local selection and lead to geographic structure and genetic divergence between populations. The southwestern United States contains many distinctive plant communities, ranging from woodlands to desert scrub, that are shaped by species adapting to local variation in elevation, precipitation, seasonality, and soils. Given this variation, species occurring across diverse habitats are expected to harbor high genetic diversity and exhibit significant genetic differences associated with environmental variation. Methodology. Here, we studied the genetic divergence of populations of Xanthisma gracile (Asteraceae) across Arizona using amplified fragment length polymorphisms and evaluated associations between genetic structure, geographic distance between populations, and variation in climatic factors. This species occurs in desert grasslands at low altitudes as well as in open pine forests at intermediate altitudes and exhibits phenotypic variation in plant height, leaf shape and pubescence, and floral traits. Pivotal results. We detected significant genetic structure across populations and found that a population from arid central Arizona is much more genetically distant than samples from northern and southern Arizona that occur in more mesic habitats. We also detected evidence for selection on numerous loci associated with variation in temperature and precipitation. Conclusions. Major changes have occurred across the Southwest since the Last Glacial Maximum, and genetic divergence in X. gracile across Arizona likely reflects selection for survival in climatically diverse habitats

Determinants of Population Genetic Structure in \u3ci\u3eChamaecrista fasciculata\u3c/i\u3e (Michx.) Greene (Fabaceae) in the Southeastern United States

Chamaecrista fasciculata is a widely distributed, phenotypically variable species in the eastern U.S. Whereas studies have demonstrated genetic structure and local adaptation in northern areas of its distribution, there has been no comparison of genetic variability among populations at the southern extent where phenotypic variation is more complex. We characterized genetic variation at 14 microsatellite loci for populations in Mississippi and Alabama and compared this to variation in a phenotypic trait, leaf pubescence. Geographic distance, climatic variables, and elevation were evaluated as factors to explain the observed patterns of genetic diversity. A significant amount of variation (19%) resided among populations, but most variation (68%) was among individuals. Assignment of individuals into genetic groups suggests two primary clusters, but these groups are not concordant with known geographical or ecological breaks, nor phenotypic variants. Genetic structure at a regional scale can be characterized as isolation by distance, while environmental factors may play a secondary role in limiting gene flow at local scales. Mean population FST is strongly associated with allelic diversity and heterozygosity, suggesting that genetic drift influences population variation. Despite the presence of genetic and phenotypic variation in southern populations of C. fasciculata, the lack of concordant patterns between these types of variation indicate that they are not driven by the same factors. This study demonstrates how local factors differentially influence the maintenance of intraspecific variation and suggest the southern distributional range is an active area of evolution for C. fasciculata

Floral and Genetic Divergence Across Environmental Gradients is Moderated by Inter-Population Gene Flow in \u3ci\u3ePlatanthera dilatata\u3c/i\u3e (Orchidaceae)

Understanding how natural selection acts on intraspecific variation to bring about phenotypic divergence is critical to understanding processes of evolutionary diversification. The orchid family is well known for pollinator-mediated selection of floral phenotypes operating among species and along environmental or geographic gradients. Its effectiveness at small spatial scales is less understood, making the geographic scale at which intraspecific floral variation is examined important to evaluating causes of phenotypic divergence. In this study, we quantified phenotypic variation in the orchid Platanthera dilatata across 26 populations in coastal Southeast Alaska and compared this to edaphic and genetic variation at microsatellite loci. We sought to determine (1) if flower morphological variation is structured at smaller geographic scales, (2) the extent of genetic divergence in relation to phenotypic divergence, (3) the scale at which inter-population gene flow occurs, and (4) the relative importance of geographic distance and abiotic factors on population genetic structure. Two morphological groups were found to separate based on lip and spur length and are restricted to different habitats. Small-flowered forms occur in muskeg bogs, whereas large-flowered forms occur in fens and meadows, and rarely in sub-alpine habitat. Genetic analyses were concordant with the morphological clusters, except for four small-flowered populations that were genetically indistinguishable from large-flowered populations and considered to be introgressed. In fact, most populations exhibited some admixture, indicating incomplete reproductive isolation between the flower forms. Pollinators may partition phenotypes but also facilitate gene flow because short-tongued Noctuidae moths pollinate both phenotypes, but longer-tongued hawkmoths were only observed pollinating the large-flowered phenotype, which may strengthen phenotypic divergence. Nevertheless, pollinator movement between habitats could have lasting effects on neutral genetic variation. At this small spatial scale, population genetic structure is only associated with environmental distance, likely due to extensive seed and pollinator movement. While this study corroborates previous findings of cryptic genetic lineages and phenotypic divergence in P. dilatata, the small scale of examination provided greater understanding of the factors that may underlie divergence

Small-Scale Population Connectivity and Genetic Structure in Canada Thistle \u3ci\u3e(Cirsium arvense)\u3c/i\u3e

Premise of research. Population connectivity, the exchange of genes among geographically separated subpopulations, is thought to be a key process for the maintenance of genetic diversity and the survival of invasive species in newly colonized areas. Plant populations\u27 degree of genetic connectivity, which occurs via pollen and seed dispersal, leads to different degrees of genetic admixture and genetic structure. Environmental barriers and differential selection pressures that are variable across time and space tend to alter genetic structure within and among populations via restriction or facilitation of gene flow. Canada thistle, an invasive species of the United States and Canada, is well known for production of high numbers of seeds, asexual reproduction, and wide environmental tolerance. These factors may influence its success as an invader by facilitating population persistence. Methodology. In this study we evaluated genetic connectivity of 12 Canada thistle populations across a 75-km area using 10 microsatellite loci, estimated the spatial scale of genetic exchange between populations, and tested for an association between genetic structure and variation in landscape characteristics. Pivotal results. All loci were highly polymorphic within populations, and populations were significantly differentiated from one another ( FST = 0.21 , p = 0.001), but environmental, geographic, and climatic factors were found to have little explanatory power for the observed genetic structure. Bayesian clustering analysis suggested the presence of two distinct genetic groups and admixture in several populations. Conclusions. We conclude that, for this species, genetic admixture and co-occurrence of genetically distinct types may play an important role in rapid adjustment to diverse environments and persistence of populations across the landscape

Phenotypic Variation of Partridge Pea \u3ci\u3e(Chamaecrista fasciculata)\u3c/i\u3e from Mississippi Persists in a Common Garden

Intraspecific phenotypic variation occurs for many different reasons and understanding its basis has applications in taxonomy, ecology, and evolution. Chamaecrista fasciculata (partridge pea) is a widely distributed species with much phenotypic variation and varied interactions with other species in communities where it grows. Botanists have often noted that phenotypic variation in some traits of this species increases from north to south in the eastern United States. In this study, we grew seeds collected from five Mississippi populations in a common greenhouse environment to determine if the observed variation in leaf and stem traits is maintained in this environment. Interpopulation variation in the greenhouse-grown plants was not as extensive as that observed under natural conditions, but significant differences were detected in the number of stems and leaves and shoot height. The number of flowers and final shoot weight of plants did not differ, suggesting that there may be multiple growth strategies for this species to achieve equal fitness. Variation was detected in stem and leaflet trichome density. The population collected at the lowest latitude showed the most distinct morphology, producing shorter plants with many branched stems, more leaves, and a higher degree of leaflet pubescence. Trait variation that has so often been observed in natural populations of this species is maintained in a common environment, suggesting a genetic basis for the observed variation. Phenotypic variation observed in this species may reflect both responses to varied selective pressures from interacting species and adaptation to differing climatic factors

Patterns of Genetic Diversity in Highly Invasive Species: Cogongrass \u3ci\u3e(Imperata cylindrica)\u3c/i\u3e Expansion in the Invaded Range of the Southern United States (US)

The spatial expansions of invasive organisms in the novel range are generally expected to follow an isolation-by-distance relationship (IBD) if the invasion is biologically driven; however, many invasions are facilitated anthropogenically. This research focused on the extant expansion patterns of cogongrass (Imperata cylindrica). Cogongrass is a widespread invasive species throughout the southern United States (US). Patterns of infestation vary among US states. Cogongrass is pyrogenic, and its invasion threatens softwood (Pinus spp.) plantations, a substantial economic market for this US region. Over 600 individuals were sampled from seven invaded US states, using amplified fragment length polymorphisms (AFLPs) to assess genetic diversity and population structure. We suspected that differences in historical management efforts among US states influenced differences in genetic diversity and structure. We detected two genetic lineages at the highest level of analysis. One genetic lineage was locally restricted, whereas the other was found throughout the study region. Admixed individuals were found in all US states and consistently co-occurred with the dominant lineage, suggesting that secondary contact and hybridization may have facilitated expansion. The widespread prevalence of only one of the two detected genetic lineages suggests a primary genetic lineage responsible for on-going population expansion in the US

Does Channel Island Acmispon (Fabaceae) Form Cohesive Evolutionary Groups?

The California Channel Islands are unique relative to other island chains due to their close proximity to the California mainland and the fact that individual islands, or groups of islands, vary in their distance to the mainland and other islands. This orientation raises questions about whether island taxa with widespread distributions form cohesive evolutionary units, or if they are actually composed of several distinct evolutionary entities, either derived from independent mainland-to-island colonization events or divergence due to prolonged allopatric isolation. The 4 northern islands are clustered in a line (6-8 km separation among islands), while the 4 southern islands are widely spaced (34-45 km separation among islands), which should impact the amount of gene flow and genetic connectivity among islands. We used nuclear microsatellite markers to examine the genetic structure and cohesion of 2 island shrubs, Acmispon dendroideus and A. argophyllus, which are widely distributed across the California Channel Islands. Both focal species contain varieties with multi-island distributions, with A. dendroideus exhibiting a greater distribution on the northern islands and A. argophyllus exhibiting a greater distribution on the southern islands. Substantial genetic divergence was observed for 2 single-island endemic varieties, A. dendroideus var. traskiae and A. agrophyllus var. niveus, confirming that allopatric isolation can lead to genetic divergence. The widespread Acmispon dendroideus var. dendroideus and single-island endemic A. dendroideus var. veatchii formed a cohesive evolutionary group that spans all 4 northern islands and 1 southern island, Santa Catalina, indicating that the northern and southern islands have been genetically linked in the past but do not display evidence of contemporary gene flow. In contrast, widespread A. argophyllus var. argenteus was composed of moderately distinct genetic groups on each of the 4 southern islands, with no evidence of recent gene flow among islands. These results demonstrate that isolation among islands has led to significant divergence among the southern islands, but that the commonly recognized split between northern and southern islands does not impact all taxa equally

The Challenges of Growing Orchids From Seeds for Conservation: An Assessment of Asymbiotic Techniques

Lewis Knudson first successfully germinated orchid seeds asymbiotically on artificial medium in 1922. While many orchid species have since been grown asymbiotically, the tremendous variation in how species respond to artificial medium and growth conditions ex situ has also become apparent in the past century. In this study, we reviewed published journal articles on asymbiotic orchid seed germination to provide a summary of techniques used and to evaluate if these differ between terrestrial and epiphytic species, to identify areas where additional research is needed, and to evaluate whether asymbiotic germination could be used more often in ex situ conservation. We found articles reporting successful asymbiotic germination of 270 species and 20 cultivars across Orchidaceae. Researchers often used different techniques with epiphytic versus terrestrial species, but species‐specific responses to growth media and conditions were common, indicating that individualized protocols will be necessary for most species. The widespread success in generating seedlings on artificial media suggests that asymbiotic techniques should be another tool for the conservation of rare orchid species. Further advances are needed in understanding how to introduce mycorrhizae to axenically grown orchids and to maximize the viability of seedlings reintroduced into natural habitats to fully utilize these methods for conservation

A Phase II study of pulse dose imatinib mesylate and weekly paclitaxel in patients aged 70 and over with advanced non-small cell lung cancer

BACKGROUND: In non-small cell lung cancer (NSCLC), interstitial hypertension is a barrier to chemotherapy delivery, and is mediated by platelet derived growth factor receptor (PDGFR). Antagonizing PDGFR with imatinib may improve intra-tumoral delivery of paclitaxel, increasing response rate (RR). METHODS: This single-stage, open-label phase II study evaluated pulse dose imatinib and weekly paclitaxel in elderly patients with advanced NSCLC. Eligible patients were aged ≥ 70 with untreated, stage IIIB-IV NSCLC and ECOG performance status 0-2. Primary endpoint was RR. Secondary endpoints included median progression free and overall survival (PFS, OS) and correlatives of PDGFR pathway activation. Baseline Charlson Comorbidity Index (CCI) and Vulnerable Elder Survey-13 (VES-13) were correlated with outcomes. RESULTS: Thirty-four patients with median age 75 enrolled. Eleven of 29 (38%) were frail by VES-13 score. Overall RR was 11/34 (32%; 95% CI 17%-51%), meeting the primary endpoint. Median PFS and OS were 3.6 and 7.3 months, respectively. High tumoral PDGF-B expression predicted inferior PFS. Frail patients by VES-13 had significantly worse median PFS (3.2 vs. 4.5 months; p=0.02) and OS (4.8 vs. 12 months; p=0.02) than non-frail. CONCLUSIONS: The combination of imatinib and paclitaxel had encouraging activity as measured by the primary endpoint of RR. However, PFS and OS were typical for elderly patients treated with single agent chemotherapy and the regimen is not recommended for further study. Adjunct imatinib did not overcome the established association of tumoral PDGF-B expression with inferior PFS. VES-13 was a powerful predictor of poor survival outcomes. Frailty should be further studied as a predictor of non-benefit from chemotherapy. TRIAL REGISTRATION: ClinicalTrials.gov NCT01011075