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Pollen viability is an important component of reproductive success, with inviable pollen causing failure of reproduction. Pollen grains have evolved mechanisms to avoid negative impacts of adverse environmental conditions on viability, including the ability to sustain ionizing radiation and repair DNA. We assessed the viability of 109,000 pollen grains representing 675 pollen samples from 111 species of plants in Chernobyl across radiation gradients that spanned three orders of magnitude. We found a statistically significant but small and negative main effect of radiation on pollen viability rates across species (Pearson's r = 0.20). Ploidy level and the number of nucleate cells (two vs. three) were the only variables that influenced the strength of the effect of radiation on pollen viability, as reflected by significant interactions between these two variables and background radiation, while there were no significant effects of genome size, pollen aperture type, life cycle duration, or pollination agent on the strength of the effect of radiation on pollen viability. Keywords: adaptation, Alexander stain, Chernobyl, indicator species, interspecific differences, pollen viability, radiation. [ABSTRACT FROM AUTHOR]

Premise of research. Gynodioecy, a dimorphic sexual system where individual plants are either female or hermaphroditic, has been documented in≪1% of plant species. This rarity suggests that gynodioecy can evolve and persist only under a restrictive set of conditions. One approach to determining these conditions is to identify the phenotypic traits and ecological factors that are associated with gynodioecy, as such traits or factors may facilitate the evolution and persistence of the sexual system. Methodology. We assembled an angiosperm-wide database of gynodioecious species and used this database to test whether gynodioecy was associated with two phenotypic traits/ecological factors: an herbaceous growth form and a temperate geographic distribution. Species-level analyses were used to confirm that gynodioecious species are predominately herbaceous and temperate. Family-level analyses were then used to test whether the presence of herbaceous and temperate species in a lineage was associated with the presence of gynodioecious species. Pivotal results. An herbaceous growth form and a temperate geographic distribution were significantly overrepresented in gynodioecious species relative to their frequency in all plant species. Families that contained species with an herbaceous growth form and a temperate geographic distribution were significantly more likely to also contain gynodioecious species. Conclusions. Gynodioecy was associated with an herbaceous growth form and a temperate distribution, suggesting that herbaceousness and temperateness can facilitate the evolution and/or persistence of gynodioecy. In addition, our results suggest that gynodioecy is associated with different phenotypic traits/ecological factors than dioecy, a closely related sexual system. Consequently, whether gynodioecy is a transitional state in the evolution of dioecy may depend on the growth form and geographic distribution of the lineage in which it evolves. [ABSTRACT FROM AUTHOR]

Premise of research. The Wisconsin Fast Plants lines of Brassica rapa (RCBr) have been a useful model system for plant ecology, evolution, physiology, and development. However, inheritance of flowering time in the B. rapa Fast Plants has not been explored. Methodology. I used quantitative genetics to explore additive, dominant, and epistatic genetic components of between-line variance in flowering time and for genotype × photoperiod interaction effects in crosses between RCBr and naturalized Californian populations. Pivotal results. Strong directional dominance for rapid flowering was evident in the F1 and F2 generations. Evidence was equivocal for epistatic genetic variance between the RCBr and California parental types. The expression of additive genetic variance for flowering time in the naturalized California populations was not masked when combined with the RCBr genetic background. A strong genotype × photoperiod interaction was found; whereas flowering time for RCBr was unaffected by day length, flowering time was halved for California plants under a 24-h photoperiod compared with that under their natural photoperiod regime. Importantly, rapid cycling was completely dominant under constant light but partially dominant under shorter photoperiods. Conclusions. Early flowering in the commonly used laboratory-derived lines of B. rapa compared with wild populations involves directional dominance that is intensified under long photoperiods. The dominance of accelerated flowering in this case contrasts with the different inheritance patterns seen in independently derived rapid cycling B. rapa lines. Generally, the apparent multiplicity of pathways available for flowering time evolution may contribute to the high incidence of local adaptation in this trait. [ABSTRACT FROM AUTHOR]

Premise of research. Invasive plants usually have growth and reproductive abilities that allow them to cope with new habitats and environments. The small balsam, Impatiens parviflora, is one of the most widespread annual invasive species in Europe. As no precise physiological assessment for this species has been performed, we compared physiological traits linked to growth performance in contrasting environments. Methodology. Plants were cultivated in growth chambers under four different treatments varying by light and water conditions. We assessed the impact of water stress and low light levels on traits related to plant growth, leaf physiology, photosynthesis, and water status. Pivotal results. Tolerance of low light level was reflected by several morphological and physiological characteristics. The number of leaves initiated was not affected by light condition, whereas specific leaf area increased for plants grown under low light. In addition, the chlorophyll fluorescence parameters revealed that low light did not affect the light-dependent reactions of photosynthesis. Although the net rate of photosynthesis was reduced, plant growth was not markedly affected. Our results thus suggest that I. parviflora generally copes well with shady conditions. The traits involved in efficiency of water use and water conservation indicated that I. parviflora is also highly tolerant to water stress. Although a reduction in plant growth and abscission of old leaves were observed after 4 wk of stress, I. parviflora demonstrated several mechanisms to maintain the light-dependent reactions of photosynthesis under water-stress conditions. Water use efficiency strongly increased in response to water stress, and plants adjusted their water potential to maintain their water supply. Conclusions. Impatiens parviflora shows physiological traits that allow plant growth under contrasting and stressful environments. These physiological traits may contribute to its invasive ability. [ABSTRACT FROM AUTHOR]

Plant-pollinator mutualisms can be disrupted in fragmented and isolated populations. Isolated populations attract fewer and less diverse pollinators, but it is not generally known whether this is due to reductions in the abundance and/or diversity of flowers at a site or to the biogeography of pollinators (or both). Islands represent one system potentially suitable to analyze the effects of spatial isolation. Here, we examine the contribution that differences in visitor composition make to increased selfing and seed production by examining the major visitors to Plectritis congesta in populations on the Gulf Islands and Vancouver Island. We find that (1) connectivity is more strongly associated with visitor assemblages and seed production than components of the floral community and (2) taking phylogeny into account suggests that increased visitation by solitary bees as opposed to other functional groups increases female fitness in P. congesta. [ABSTRACT FROM AUTHOR]

Premise of research. Genetic variation for ecologically important traits is necessary for populations to adapt to environmental change. Many authors have called for a greater emphasis on directly measuring quantitative genetic variation in rare species, which are expected to have reduced amounts of genetic variation due to genetic drift in small populations. The extent of among-population differentiation for quantitative traits may also help to evaluate the likelihood that genetic rescue/translocation will be a successful conservation strategy. Despite these merits, relatively few studies measure quantitative genetic variation for ecologically important traits as a function of population size. Methodology. Sixteen populations of the endangered plant Hypericum cumulicola were sampled, capitalizing on previous work that has estimated relative effective population sizes and demonstrated minimal migration between populations. This context allows more direct inference about the role of drift in small populations on quantitative genetic variation, the focus of this study. Using controlled pollinations and a greenhouse common garden, quantitative genetic variation within populations and differentiation among populations were estimated for six putatively ecologically important traits. Pivotal results. There were few significant estimates of genetic variation for most traits irrespective of population size. There was a positive correlation between population size and genetic variation for anther-stigma distance, a floral trait expected to influence the degree of self-fertilization. There was also limited differentiation among populations for all traits. Conclusions. Limited genetic variation for ecologically important traits in these populations could slow or limit adaptive responses to future environmental change, possibly increasing extinction risk. The smallest populations will be particularly sensitive to environmental/habitat changes that result in reduced pollinator visitation. Limited phenotypic differentiation, combined with previous evidence of strong heterosis in crosses between small populations, suggests little risk of outbreeding depression if genetic rescue efforts become necessary to preserve this species. [ABSTRACT FROM AUTHOR]

Premise of research. Sex allocation, the relative energy devoted to producing pollen, ovules, and floral displays, can significantly affect reproductive output and population dynamics. In this study, we investigated floral morphology and gamete production in bisexual, distylous plants from a self-incompatible hybrid complex (Piriqueta cistoides ssp. caroliniana Walter [Arbo]; Turneraceae). Sampling focused on two parent types (C, V) and their stable hybrid derivative (H). Since H morphotypes are heterotic for growth and fruit production, we hypothesized that they would produce larger flowers with more gametes. We also anticipated that plants with long styles (long morphs) would produce less pollen than short morphs, since long-morph pollen is larger. Methodology. Over two consecutive summers, flowers were collected from 1465 individual plants in 28 field populations. Floral parameters were measured digitally, and each flower's pollen number, ovule number, and stigma-anther separation was quantified under a dissecting microscope. Gamete production (n = 332) and stigma-anther separation (n = 119) were also quantified for plants from a greenhouse accession. Pivotal results. Floral display differed among morphotypes, with H plants producing the largest flowers and C plants displaying the least petal separation. Hybrid morphotypes produced significantly more pollen than parental morphotypes, and pollen quantity was significantly greater for long morphs. Ovule production, however, was greatest for V flowers. Stigma-anther separation differed between years and style morphs (greater for short morphs) but not among morphotypes or within a single season. Conclusions. Differences in pollen production between morphs were not consistent with trade-offs in pollen size and number or selection for increased male function in short morphs. Greater stigma-anther separation in short morphs supported the hypothesis of selection to reduce pollen interference. Enhanced floral display and pollen production followed other heterotic traits observed in H morphotypes. The superior ability of H morphotypes to attract pollinators and sire seeds might partially explain this hybrid zone's continuing expansion. [ABSTRACT FROM AUTHOR]

Natural populations of wild radish harbor 20-fold phenotypic variation in seed weight. Under competitive conditions, the weight of sown seeds is positively correlated phenotypically with final plant stature, lifetime flower production, lifetime fruit production, and seed production. To establish the evolutionary significance of seed-weight variation in a natural population, I conducted reciprocal crosses among individuals chosen from a wild population in Connecticut. The progeny were sown in an experimental garden, and an analysis of 12 life history and fitness components was conducted on the paternal half sibs. This design provided estimates of the narrow-sense and broad-sense heritabilities of the weight of sown seeds (produced by the parental generation), germination and flowering dates, 7 fitness components, the weight of seeds produced by F$_1$ adults, and lifetime maternal fecundity. The results suggest that natural selection could not operate to effect evolutionary change in seed weight in this experimental population. Maternal environmental effects, non-additive genetic effects, and/or developmental sources of variation are largely responsible for the phenotypic variance in seed weight in wild radish. Additive genetic variance was detected in several life history and fitness components, suggesting that additive genetic variance in total fitness exists within this population. [ABSTRACT FROM AUTHOR]