Pollination decays in biodiversity hotspots Vamosi, J.C; Knight, T.M; Steets, J.A ...
Proceedings of the National Academy of Sciences - PNAS,
01/2006, Letnik:
103, Številka:
4
Journal Article
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As pollinators decline globally, competition for their services is expected to intensify, and this antagonism may be most severe where the number of plant species is the greatest. Using meta-analysis ...and comparative phylogenetic analysis, we provide a global-scale test of whether reproduction becomes more limited by pollen receipt (pollen limitation) as the number of coexisting plant species increases. As predicted, we find a significant positive relationship between pollen limitation and species richness. In addition, this pattern is particularly strong for species that are obligately outcrossing and for trees relative to herbs or shrubs. We suggest that plants occurring in species-rich communities may be more prone to pollen limitation because of interspecific competition for pollinators. As a consequence, plants in biodiversity hotspots may have a higher risk of extinction and/or experience increased selection pressure to specialize on certain pollinators or diversify into different phenological niches. The combination of higher pollen limitation and habitat destruction represents a dual risk to tropical plant species that has not been previously identified.
As a step toward understanding how community context shapes mating system evolution, we investigated the combined role of two plant antagonisms, vegetative herbivory and intraspecific competition, ...for reproduction and mating system expression (relative production of selfing, cleistogamous and facultatively outcrossing, chasmogamous flowers and fruits) of Impatiens capensis. In a survey of I. capensis populations, we found that vegetative herbivory and intraspecific competition were positively correlated. In a greenhouse experiment where leaf damage and plant density were manipulated, multispecies interactions had dramatic effects on reproductive and mating system traits. Despite having additive effects on growth, herbivory and competition had nonadditive effects for mating system expression, chasmogamous fruit production, flower number and size, and cleistogamous flower production. Our results demonstrate that competitive interactions influence the effect of herbivory (and vice versa) on fitness components and mating system, and thus antagonisms may have unforeseen consequences for mating system evolution, population genetic diversity, and persistence.
The physiological cost of reproduction was investigated in a perennial plant species, Sidalcea oregana ssp. spicata. Two different classes of estimates of current reproductive investment were ...compared, with the goal of identifying the most powerful predictor of future reproductive effort. "Static" estimates, those typically used to measure current reproductive investment (i.e., biomass or nutrients allocated to reproduction), neglect the physiological processes that influence actual reproductive expenditure. Conversely, "dynamic" estimates that incorporate reproductive photosynthesis or respiration, nectar production, or reproductive nutrient resorption offer a more accurate assessment of current reproductive investment. I assessed the potential for nutrient resorption from senescing reproductive structures to mitigate the cost of reproduction. Significant proportions of nitrogen and phosphorus were resorbed from floral structures, but structures differed in resorption potential and efficiency. Moreover, dynamic estimates of nutrient investment were better predictors of future reproductive effort than were static estimates. Dynamic estimates appear to be closer indicators of realized physiological cost of reproduction. By taking a dynamic perspective of reproductive investment, we may be better equipped to address the potential for evolutionary change in life history and sex allocation in plants.
Gender‐dimorphic plants are often subject to sex‐differential enemy attack, but whether and how this contributes to trait evolution is unknown. To address this gap, we documented the spatiotemporal ...prevalence of sex‐biased weevil damage in a gynodioecious strawberry. We then conducted path analysis to evaluate the direct and indirect pathways for weevils to affect female and male fertility and to mediate selection in two experimental gardens. Direct effects of weevils significantly reduced fertility and mediated selection on reproductive traits, even in the nonpreferred sex (females). Weevils significantly reduced floral display size in hermaphrodites in both gardens, and this translated into a substantial negative indirect effect on male fertility in the garden where the pathway to fertility via display was stronger. Thus, indirect effects of weevils can contribute to selection in hermaphrodites, which gain the majority of their fitness via male function. Our results also indicate that weevils often play a larger role than pollinators in shaping reproductive phenotype and thus raise the intriguing possibility that antagonists may be drivers of sexual dimorphism. Finally, our results support the view that mutualists, antagonists, and the abiotic environment should be considered when attempting to understand reproductive trait evolution in gender‐dimorphic species.
A total of 45 primary head and neck squamous cell carcinomas were analysed by comparative genomic hybridisation to identify regions of chromosomal deletion and gain. Multiple regions of copy number ...aberration were identified including gains affecting chromosomes 3q, 8q, 5p, 7q, 12p and 11q and deletion of material from chromosomes 3p, 11q, 4p, 5q, 8p, 10q, 13q and 21. Kaplan-Meier survival analysis revealed significant correlations between gain of 3q25-27 and deletion of 22q with reduced disease-specific survival. In addition, gain of 17q and 20q, deletion of 19p and 22q and amplification of 11q13 were significantly associated with reduced disease-free survival. A Cox proportional hazards regression model identified deletion of 22q as an independent prognostic marker. The data presented here provide further evidence that the creation of a genetically based tumour classification system will soon be possible, complementing current histopathological characterisation.
Gynodioecious plants exhibit modest sexual dimorphism in vegetative and phenological traits, which stands in stark contrast to pronounced dimorphism in reproductive traits. I evaluate the roles of ...limited genetic variation, negative genetic covariation (within and between sex morphs), and lack of gender‐differential selection in contributing to minimal sexual dimorphism for these traits inFragaria virginiana. Major findings are as follows. First, selection was sometimes differential but rarely divergent between male and female fertility modes. Second, response to selection was constrained by low genetic variation and extensive genetic covariance. In fact, covariance between traits within sex morphs appears to represent a constraint on par with that of covariance between sex morphs. Third, these constraints combine with different modes of gamete transmission to produce very different gender‐specific contributions to the mean phenotypes of the next generation. Finally, predicted responses to selection for several traits are concordant with the degree and direction of dimorphism in a closely related dioecious species. In sum, this work suggests that minimal sexual dimorphism in vegetative and phenological traits is due to similar directional selection via male and female fertility combined with the constraints of low genetic variation and extensive genetic covariance both within and between sex morphs.
To understand how genetic constraints may limit the evolution of males and sexual dimorphism in a gynodioecious species, I conducted a quantitative genetic experiment in a gynodioecious wild ...strawberry, Fragaria virginiana. I estimated and compared genetic parameters (narrow-sense heritabilities, between-trait and between-sex genetic correlations, as well as phenotypic and genetic variance-covariance matrices) in the two sex morphs from three populations grown in a common field garden. I measured pollen and ovule production per flower, petal size, fruit set, and flower number. My major findings are as follows. (1) The presence of a phenotypic trade-off between pollen production and fruit set in hermaphrodites reflects a negative genetic correlation in the narrow sense that is statistically significant when pooled across populations. (2) The main constraints on the evolution of males are low genetic variation for pollen per flower and strong positive correlations associated with ovule number (e.g., between pollen and ovules in hermaphrodites, and between ovules in hermaphrodites and females). (3) Traits with the lowest levels of sexual dimorphism (ovule number and flower number) have the highest between-sex genetic correlations suggesting that overlap in the expression of genes in the sex morphs constrains their independent evolution. (4) There are significant differences in G matrices between sex morphs but not among populations. However, evidence that male-female trait correlations in hermaphrodites were lower in populations with higher frequencies of females may indicate subtle changes in genetic architecture.
Most flowering plants rely on animal pollinators to transfer male gametes between individuals, and thus a significant problem for gender dimorphic plants is that pollinators often avoid female ...flowers. Here we show for the first time that one important reason pollinators shun female flowers is because they do not smell like males. We compared emission rates and floral scent composition in a gynodioecious wild strawberry (Fragaria virginiana) where females receive half as many visits by generalist pollinators as conspecific hermaphrodites. We used floral extracts to determine the source of sexually dimorphic odor and pollinator responses. Specifically, we used extracts of whole flowers and specific floral parts in choice tests to determine that pollinators preferred the scent of hermaphrodite flowers over those of females and that this discrimination was due primarily to the scent of hermaphrodite anthers. These data conclusively show that scent can be a major driver of pollinator behavior in gender dimorphic plants. Our results also indicate that scent is an important modulator of pollinator behavior even in a small flowered, weakly scented species visited by generalist pollinators, and not just peculiar to intensely scented, deceptive, or specialized pollination systems.
The component parts of modular organisms often show interspecific variation in their longevity. In plants, the flower is an example of such a structure. Models are developed in this paper to predict ...optimal floral longevity (the optimal length of time that flowers should remain open and functional) under a variety of conditions. A trade-off involving allocation of resources to floral construction versus floral maintenance is assumed. The main model variables are the rate at which pollen and seed fitness accrue over time (fitness-accrual rates) and the daily cost of maintaining an existing flower relative to the cost of constructing a new one (floral maintenance cost). Long-lived flowers are selected when fitness-accrual rates and floral maintenance costs are low, whereas short-lived flowers are selected when fitness-accrual rates and floral maintenance costs are high. Dichogamy favors longer-lived flowers relative to homogamy, whereas nonindependence among flowers in their attractiveness to pollinators (attraction to flower clusters) selects for shorter-lived flowers. Reduction in floral maintenance costs later on in the flower's life favors longer-lived flowers. Observations on the dissemination and receipt of pollen in individual flowers over time, together with measurements of corolla respiration and nectar sugar production rate are required to test the model quantitatively. The parameters important to the evolution of optimal floral longevity (i.e., maintenance and construction costs, and fitness-accrual rates) may be general features of evolution of optimal longevities of other repeated structures.
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