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1.
? In natural communities, plants can receive pollen from multiple heterospecifics as well as conspecifics. However, studies on the effects of interspecific pollen transfer have focused on interactions between species pairs. The potential exists for diverse interactions among heterospecific pollen (HP) grains on the stigma, and for these to affect plant reproduction, alone or in combination with conspecific pollen (CP) loss, but these interactions have not yet been explored. ? We used hand-pollinations to simulate increasing community diversity and CP loss on Mimulus guttatus stigmas. We used pollen mixes of one to three heterospecific donors to determine how species composition and CP load size affect seed production and to characterize the mechanisms underlying fertilization failure. ? Heterospecific pollen deposition reduced M. guttatus seed production and while the effect increased with the number of heterospecific donors, the strength depended on species composition and was independent of conspecific load size. Different types of interactions (additive and synergistic) are hypothesized to underlie the diverse effects on M. guttatus reproductive success. ? Our results suggest that an increase in the diversity of heterospecific donors will not always lead to a greater decrease in fitness because multispecies effects depend on the interacting species.  相似文献   
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  总被引:1,自引:0,他引:1  
Abstract 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.  相似文献   
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One might predict that cytochalasin D, which slows polymerization of actin in solution and which inhibits actin-containing microfilament function in live B lymphocytes, would also prevent actin polymerization in these cells. However, we have used the NBD-Phallacidin flow cytometric assay for F-actin and the DNase I inhibition assay for G-actin to demonstrate that cytochalasin D (at 20 micrograms/ml and higher) stimulates actin polymerization in murine B lymphocytes within the first 30 sec of exposure. A similar response was seen in human neutrophils. Actin polymerization induced in neutrophils by chemotactic peptides has been linked to activation of the polyphosphoinositide-calcium increase-protein kinase C signal transduction pathway. As B lymphocytes also transduce signals using this pathway, we investigated whether cytochalasin D induced actin polymerization by activating this pathway. Cytochalasin D and ionomycin both stimulated a rapid increase in internal calcium (by 1 min) in the B cell which was inhibitable by EGTA, implicating calcium influx. Ionomycin also induced actin polymerization, detectable later, by 10 min. EGTA blocked the ionomycin-induced actin polymerization, but not that induced by cytochalasin D. Cytochalasin D-induced actin polymerization was not associated with detectable hydrolysis of polyphosphoinositides, nor was it inhibited by H7 (a protein kinase C inhibitor) or by HA1004 (an inhibitor of cyclic nucleotide-dependent kinases). Furthermore, anti-immunoglobulin antibodies, which stimulate B lymphocytes through the polyphosphoinositide hydrolysis-calcium increase-protein kinase C pathway, failed to induce actin polymerization in these cells. These antibodies did, however, stimulate the cells to perform activities that involve actin-containing microfilaments. Other primary activators of B lymphocytes (dextran sulfate, PMA, and LPS) and a panel of lymphokines previously shown to enhance B lymphocyte activation (IL-1, IL-2, IL-4, IL-5) were also screened in the F-actin assay and no evidence for actin polymerization was found. We conclude that the actin polymerization response to cytochalasin D in the B cell does not involve the polyphosphoinositide hydrolysis-calcium increase-protein kinase C pathway, nor does it depend on cyclic nucleotide-dependent kinases. Furthermore, our studies failed to provide any evidence that early actin polymerization occurs in murine B lymphocyte activation.  相似文献   
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Initial velocity studies can be used to define the function of chemically modifiable residues in the active site of a multisubstrate enzyme. Since the method relies on measuring biological activity, it has the advantage that it can be used with small amounts of relatively impure enzyme, but requires that modified enzyme molecules have some residual catalytic activity. The kinetic analysis of the modified enzyme can be carried out in the presence of some unmodified enzyme molecules. Consideration of examples of single- and multisubstrate enzymic reactions shows that interpretation of changes in apparent Km and apparent V values following chemical modification, in terms of effects on substrate binding or catalysis or both, requires a detailed knowledge of the kinetic reaction sequence. In the case of multisubstrate enzymes, it is necessary to ensure that, during the kinetic investigation, the concentrations of the non-varied substrates remain at near-saturating levels. For this reason, and because modification may induce changes in the rate-limiting step, a full kinetic analysis of the modified enzyme is advisable.  相似文献   
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Reproductive allocation was investigated in female and hermaphrodite plants of gynodioecious Sidalcea oregana ssp. spicata. Total reproductive investment and partitioning of that investment was documented at the level of whole plants in terms of four ecologically relevant currencies: biomass, nitrogen, phosphorus, and potassium. Nutrient augmentations in the field confirmed that nutrients were limiting plant vegetative growth and propensity to flower; thus the use of these nutrients as currency was appropriate. Once the effects of plant size were removed, the sex morphs allocated similar total amounts of biomass, nitrogen, phosphorus, and potassium to reproduction, but partitioned those differentially. For any given individual size, females allocated larger proportions of their reproductive resource budgets to seeds. Hermaphrodites' reproductive investment in pollen and flowers was allocated at the expense of allocation to seeds. These data are relevant to the evolution of gynodioecy from hermaphroditism and support the hypothesis that females reallocate resources not spent on pollen to seeds.  相似文献   
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Trait selection in flowering plants: how does sexual selection contribute?   总被引:1,自引:1,他引:1  
By highlighting and merging the frameworks of sexual selectionenvisioned by Arnold (1994) and Murphy (1998), we discuss howsexual selection can occur in plants even though individualsdo not directly interact. We review studies on traits that influencepollen export and receipt in a variety of hermaphroditic andgynodioecious plants with the underlying premise that pollinationdynamics influences mate acquisition. Most of the studies reviewedfound that phenotypes that enhance pollen export are in harmonywith those that enhance pollen receipt suggesting that in manycases pollinator visitation rates limit both male and femalefunction. In contrast, fewer traits were under opposing selection;but when they were, the traits most often were associated withenhancing the specific aspects of a given sex function. Ourreview helps clarify and illustrate why sexual selection canbe a component of trait evolution in hermaphrodite plants.  相似文献   
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Polyploidy has been hypothesized to be both an evolutionary dead-end and a source for evolutionary innovation and species diversification. Although polyploid organisms, especially plants, abound, the apparent nonrandom long-term establishment of genome duplications suggests a link with environmental conditions. Whole-genome duplications seem to correlate with periods of extinction or global change, while polyploids often thrive in harsh or disturbed environments. Evidence is also accumulating that biotic interactions, for instance, with pathogens or mutualists, affect polyploids differently than nonpolyploids. Here, we review recent findings and insights on the effect of both abiotic and biotic stress on polyploids versus nonpolyploids and propose that stress response in general is an important and even determining factor in the establishment and success of polyploidy.  相似文献   
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Ecological opportunity is a powerful driver of evolutionary diversification, and predicts rapid lineage and phenotypic diversification following colonization of competitor‐free habitats. Alternatively, topographic or environmental heterogeneity could be key to generating and sustaining diversity. We explore these hypotheses in a widespread lineage of Australian lizards: the Gehyra variegata group. This clade occurs across two biomes: the Australian monsoonal tropics (AMT), where it overlaps a separate, larger bodied clade of Gehyra and is largely restricted to rocks; and in the larger Australian arid zone (AAZ) where it has no congeners and occupies trees and rocks. New phylogenomic data and coalescent analyses of AAZ taxa resolve lineages and their relationships and reveal high diversity in the western AAZ (Pilbara region). The AMT and AAZ radiations represent separate radiations with no difference in speciation rates. Most taxa occur on rocks, with small geographic ranges relative to widespread generalist taxa across the vast central AAZ. Rock‐dwelling and generalist taxa differ morphologically, but only the lineage‐poor central AAZ taxa have accelerated evolution. This accords with increasing evidence that lineage and morphological diversity are poorly correlated, and suggests environmental heterogeneity and refugial dynamics have been more important than ecological release in elevating lineage diversity.  相似文献   
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