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Premise The timing of self-fertilization has potentially important consequences for the trajectory of mating system evolution, the opportunity for outcrossing, and the maintenance of genetic variation in populations. For primarily selfing taxa, it remains poorly understood as to how floral variation influences the opportunity for outcrossing and whether those attributes vary among populations across geographic ranges. Methods We examined variation in floral traits (herkogamy, protandry, flower size, stigma stage at anthesis, timing of stigma receptivity) in seven populations of Clarkia xantiana ssp. parviflora, a primarily selfing taxon, spanning from the western to eastern margins of its distribution. We also performed experimental emasculations and pollinations (followed by stigma severing) to quantify the extent of opportunities for outcrossing across flower development. Results There was marked among-population variation in all floral traits, particularly between far eastern and western populations. Emasculation experiments showed that the eastern populations had minimal autonomous selfing, but western populations had high rates of selfing within 24 h after anthesis. Population variation in autofertility was significantly predicted by floral trait variation, especially protandry and petal size. Conclusions Greater protandry both extended the time over which outcrossing could potentially occur and reduced the probability of autonomous selfing, suggesting that there may be a tradeoff that results in fitness loss when pollinator visits are not common. The east-west pattern of differentiation in some floral traits parallels that of postglacial range expansion, suggesting that selection on the mating system may have been strong in the process of range expansion.

Premise of research. The serpentine grassland system provides the opportunity to examine whether drought response traits may have contributed to differentiation in the stress-tolerant genus Clarkia. Commonly utilized drought responses might be indicative of traits important to species diversification in stressful environments.Methodology. We examined the drought response strategies of populations of Clarkia gracilis (Onagraceae) from both serpentine and nonserpentine soils. Physiological, morphological, and biomass data were collected under controlled greenhouse conditions.Pivotal results. Serpentine-derived plants exhibited faster growth and germination rates and larger leaf size than nonserpentine-derived plants under increasing water stress, indicating drought escape strategies. However, serpentine-derived plants also employed dehydration avoidance by increasing their water-use efficiency (decreased transpiration rate) under drought stress. In terms of biomass, serpentine-derived plants had a higher fi...

PREMISE OF THE STUDY The persistence of rare and endangered plant species may depend on the distance pollinators travel when dispersing pollen. Pollinations between adjacent plants, which are often genetically similar, can decrease seed set, germination, and/or progeny vigor due to shared S-alleles or inbreeding depression. Interpopulation pollen dispersal is often suggested as a management tool to increase genetic diversity; however, long-distance pollinations also have the potential to decrease fitness. METHODS We performed experimental hand pollinations in the field and germination experiments in a growth chamber to determine the effect of intrapopulation pollination distance (1 m, 10 m, and 100 m) on seed set, seed germination, progeny growth, and progeny reproduction in Phlox hirsuta. In addition, we included interpopulation pollinations (6740 m) to determine whether artificial gene flow is a viable management option for this endangered species. KEY RESULTS Although pollination distance did not affect the number of healthy seeds produced or the likelihood of radicle emergence, it did significantly affect the ability of germinating seeds to successfully produce cotyledons. Outbreeding depression was observed during seed germination and early seedling development. Seedlings resulting from interpopulation pollinations developed more slowly and were less likely to survive to produce cotyledons than seedlings resulting from all three intrapopulation pollination distances. CONCLUSIONS Our results suggest that the success of P. hirsuta does not depend on the distance pollinators travel within populations and that conservation strategies that involve transporting genes between populations can be counterproductive.

Premise of the study: The three-dimensional structure of tree canopies creates environmental heterogeneity, which can differentially influence the chemistry, morphology, physiology, and/or phenology of leaves. Previous studies that subdivide canopy leaves into broad categories (i.e., “upper/lower”) fail to capture the differences in microenvironments experienced by leaves throughout the three-dimensional space of a canopy. Methods: We use a three-dimensional spatial mapping approach based on spherical polar coordinates to examine the fine-scale spatial distributions of photosynthetically active radiation (PAR) and the concentration of ultraviolet (UV)-absorbing compounds (A300) among leaves within the canopies of black mangroves (Avicennia germinans). Results: Linear regressions revealed that interior leaves received less PAR and produced fewer UV-absorbing compounds than leaves on the exterior of the canopy. By allocating more UV-absorbing compounds to the leaves on the exterior of the canopy, black mangroves may be maximizing UV-protection while minimizing biosynthesis of UV-absorbing compounds. Discussion: Three-dimensional spatial mapping provides an inexpensive and portable method to detect fine-scale differences in environmental and biological traits within canopies. We used it to understand the relationship between PAR and A300, but the same approach can also be used to identify traits associated with the spatial distribution of herbivores, pollinators, and pathogens.

BACKGROUND The soil environment can affect not only the quantity of crops produced but also their nutritional quality. We examined the combined effects of below-ground cadmium (0, 5, and 15 ppm) and mycorrhizal fungi (presence and absence) on the concentration of five major fatty acids within flax seeds (Linum usitatissimum). RESULTS Plants grown with mycorrhizal fungi produced seeds that contained higher concentrations of unsaturated (18:1, 18:2 and 18:3), but not saturated (16:0 and 18:0) fatty acids. The effects of mycorrhizal fungi on the concentration of unsaturated fatty acids in seeds were most pronounced when plant roots were exposed to 15 ppm Cd (i.e. the concentrations of 18:1, 18:2 and 18:3 increased by 169%, 370% and 150%, respectively). CONCLUSIONS The pronounced effects of mycorrhizal fungi on the concentration of unsaturated fatty acids at 15 ppm Cd may have been due to the presence of elevated levels of Cd within seeds. Our results suggest that, once the concentration of cadmium within seeds reaches a certain threshold, this heavy metal may improve the efficiency of enzymes that convert saturated fatty acids to unsaturated fatty acids. © 2014 Society of Chemical Industry

Background and aims Natural variation in fruit and seed set may be explained by factors that affect the composition of pollen grains on stigmas. Self-incompatible species require compatible outcross pollen grains to produce seeds. The siring success of outcross pollen grains, however, can be hindered if self (or other incompatible) pollen grains co-occur on stigmas. This study identifies factors that determine fruit set in Phlox hirsuta, a self-sterile endangered species that is prone to self-pollination, and its associated fitness costs. Methods Multiple linear regressions were used to identify factors that explain variation in percentage fruit set within three of the five known populations of this endangered species. Florivorous beetle density, petal colour, floral display size, local conspecific density and pre-dispersal seed predation were quantified and their effects on the ability of flowers to produce fruits were assessed. Key results In all three populations, percentage fruit set decreased as florivorous beetle density increased and as floral display size increased. The effect of floral display size on fruit set, however, often depended on the density of nearby conspecific plants. High local conspecific densities offset - even reversed - the negative effects of floral display size on percentage fruit set. Seed predation by mammals decreased fruit set in one population. Conclusions The results indicate that seed production in P. hirsuta can be maximized by selectively augmenting populations in areas containing isolated large plants, by reducing the population sizes of florivorous beetles and by excluding mammals that consume unripe fruits.

Premise of research. Hermaphroditic plants with self-incompatible mating systems often produce flowers that fail to mature seed-containing fruits. A variety of factors can affect reproductive success in these species, including pollen load size, pollen viability, pollen-pistil compatibility, and self-pollen interference. We combined field, growth chamber, and laboratory studies to identify factors that are and are not responsible for high ovule-to-seed ratios in Phlox hirsuta, a self-sterile, hermaphroditic, endangered species.Methodology. We (1) determined whether pollen load size affected seed set by counting the number of grains on stigmas following natural pollinations and following outcross-only pollinations, (2) assessed pollen viability by staining grains collected from flowers of different ages, (3) quantified the degree of autonomous self-pollination by counting the number of self-pollen grains that accumulated on stigmas over time, and (4) determined whether self pollen on stigmas interfered wit...

PREMISE OF THE STUDY Agricultural soils have become contaminated with a variety of heavy metals, including cadmium. The degree to which soil contaminants affect plants may depend on symbiotic relationships between plant roots and soil microorganisms. We examined (1) whether mycorrhizal fungi counteract the potentially negative effects of cadmium on the growth and fitness of flax (Linum usitatissimum) and (2) whether mycorrhizal fungi affect the accumulation of cadmium within plant parts. METHODS Two flax cultivars (Linott and Omega) were grown in three soil cadmium environments (0, 5, and 15 ppm). Within each cadmium environment, plants were grown in either the presence or absence of mycorrhizal fungi. Upon senescence, we measured growth and fitness and quantified the concentration of cadmium within plants. KEY RESULTS Soil cadmium significantly decreased plant fitness, but did not affect plant growth. Mycorrhizal fungi, which were able to colonize roots of plants growing in all cadmium levels, significantly increased plant growth and fitness. Although mycorrhizal fungi counteracted the negative effects of cadmium on fruit and seed production, they also enhanced the concentration of cadmium within roots, fruits, and seeds. CONCLUSIONS The degree to which soil cadmium affects plant fitness and the accumulation of cadmium within plants depended on the ability of plants to form symbiotic relationships with mycorrhizal fungi. The use of mycorrhizal fungi in contaminated agricultural soils may offset the negative effects of metals on the quantity of seeds produced, but exacerbate the accumulation of these metals in our food supply.

Mating system can impact the frequency of hybridization and therefore the maintenance of species diversity. I evaluate the effects of weak self-incompatibility (SI) in Phlox cuspidata and SI in Phlox drummondii on mating success within species and on hybridization dynamics between species under controlled conditions. The effects of SI on hybridization frequency were assessed by manipulating the relatedness of conspecific pollen and the relative timing of pollen deposition in mixed-donor interspecific pollinations. Selfing as opposed to outcrossing increased hybridization by 16% in P. cuspidata maternal plants and by 48% in P. drummondii maternal plants because self pollen did not compete as well against heterospecific pollen. The relative timing of conspecific versus heterospecific pollen deposition also impacted hybridization. In self-compatible P. cuspidata, the deposition of self pollen 5 h earlier than heterospecific pollen decreased hybridization by 28%. In self-incompatible P. drummondii, a 5 h delay in the deposition of compatible conspecific pollen increased hybridization by 32%. In this hybrid system, early self-pollination can decrease hybridization (but increase inbreeding) by P. cuspidata maternal plants, and SI may increase hybridization by P. drummondii maternal plants.

Pollen competition between species strongly influences hybridization dynamics in plants. By performing single- and mixed-donor pollinations, we show that soil Ca alters the outcome of interspecific pollen competition in the annual Phlox hybrid system of Phlox cuspidata and P. drummondii. In the absence of interspecific pollen competition, heterospecific pollen siring success of both species was influenced most strongly by the maternal growth environment, such that hybridization was facilitated when heterospecific pollen was deposited on stigmas of maternal plants growing in high Ca soils. When heterospecific pollen was forced to compete against conspecific pollen, however, the maternal growth environment did not influence hybridization, but the environmental origin of heterospecific pollen did, and this effect depended on the maternal species. Pollen of P. drummondii was more effective at outcompeting P. cuspidata pollen and preventing hybridization in P. drummondii dams when P. cuspidata pollen was derived from low Ca. Pollen competition within pistils of P. cuspidata was unaffected by pollen Ca environment. In situations in which P. cuspidata grows in lower soil Ca than P. drummondii, as has been documented in one population, these results suggest that the competitive ability of heterospecific pollen will be diminished by environmental effects of soil Ca. Thus, the environment in which pollen develops can influence interspecific pollen competition and hybridization frequency.

Postpollination mechanisms of reproductive isolation can critically influence the amount of gene flow between hybridizing species. While much evidence exists for genetically based pollen-pistil incompatibility, we show that environmental variation also influences the postpollination performance of heterospecific pollen in the annual Phlox hybrid system. Thus, the environmental segregation of species can influence hybridization dynamics. We found that P. cuspidata was restricted to soils of low Ca concentrations in the field and performed better under experimentally low Ca; P. drummondii was able to inhabit high-Ca soils and sometimes performed better in this environment. To determine whether soil Ca influenced pollen-pistil compatibility in a manner that alters pollen siring success, single-donor pollinations were performed in a completely factorial crossing design between species, maternal Ca environments, and paternal Ca environments. Maternal and paternal environments interacted in their effects on pollen-pistil compatibility for both inter- and intraspecific crosses, such that pollen performance was highest when mothers and fathers were grown in different soil Ca environments. These results suggest that when Phlox species predictably inhabit different environments, environmental heterogeneity can impede the processes of speciation and local adaptation by enhancing the performance of pollen dispersed across species and environments.

The soil environment can affect not only the quantity of crops produced but also their nutritional quality. We examined the combined effects of below-ground cadmium (0, 5, and 15 ppm) and mycorrhizal fungi (presence and absence) on the concentration of five major fatty acids within flax seeds (Linum usitatissimum).Plants grown with mycorrhizal fungi produced seeds that contained higher concentrations of unsaturated (18:1, 18:2 and 18:3), but not saturated (16:0 and 18:0) fatty acids. The effects of mycorrhizal fungi on the concentration of unsaturated fatty acids in seeds were most pronounced when plant roots were exposed to 15 ppm Cd (i.e. the concentrations of 18:1, 18:2 and 18:3 increased by 169%, 370% and 150%, respectively).The pronounced effects of mycorrhizal fungi on the concentration of unsaturated fatty acids at 15 ppm Cd may have been due to the presence of elevated levels of Cd within seeds. Our results suggest that, once the concentration of cadmium within seeds reaches a certain threshold, this heavy metal may improve the efficiency of enzymes that convert saturated fatty acids to unsaturated fatty acids.

The goal of this interdisciplinary activity is to encourage students to think critically about the ethical, environmental, and human health consequences of producing and consuming processed foods.