Floral reduction in Crepis tectorum (Asteraceae): tradeoffs and dominance relationships

The present investigation of Crepis tectorum examines the extent to which tradeoffs and patterns of dominance contribute to the association between flower size (head width) and degree of self-fertility among populations adapted to rock outcrops. Partial correlation analyses of phenotypic data from a F2 generation derived from a cross between two outcrop plants and of family means representing one of the parent populations indicate that small-flowered plants fail to reallocate resources to flower and fruit production, that small flower size offers little or no advantage in terms of autofertility, and that floral reduction has little influence on the rate of flower development. Hence, it may be necessary to invoke factors other than tradeoffs to explain the decline in flower size associated with the evolution of autogamy in C. tectorum. Comparison of parent and Fl hybrid means in the crossing experiment suggests incomplete dominance in the alleles for large flower size. Under the assumption that Fl hybrid means reflect the average degree of dominance across loci, I propose inbreeding depression as the basis for some of the reduction in floral morphology.     

Florivory increases selfing: an experimental study in the wild strawberry, Fragaria virginiana

Florivores are antagonists that damage flowers, and have direct negative effects on flowering and pollination of the attacked plants. While florivory has mainly been studied for its consequences on seed production or siring success, little is known about its impact on mating systems. Damage to flowers can alter pollinator attraction to the plant and may therefore modify patterns of pollen transfer. However, the consequences of damage for mating systems can take two forms: a decrease in flower number reduces opportunities for intra-inflorescence pollen deposition (geitonogamy), which, in turn, may lead to a decrease in selfing; whereas a decrease in floral display may also reduce overall visitation and thus increase the chances of self-pollination via facilitated or autonomous autogamy. We investigated the effects of damage by a bud-clipping weevil ( Anthonomus signatus ) in Fragaria virginiana in an experimental setting mimicking natural conditions. We found that increased damage led to an increase in selfing, a result consistent with the increased autogamy pathway. We discuss the implications of this finding and evaluate the generality of florivore-mediated mating system expression.     

Pollen limitation and natural selection on floral characters in the yellow monkeyflower, Mimulus guttatus

In flowering plants, pollen limitation has been proposed to intensify selection on floral characters important in pollinator attraction, but may also select for traits that increase seed set through autonomous selfing. Here, a factorial design (+/- pollen addition, +/- pollinator removal) was used to investigate how the pollination environment affects selection on floral morphology via female fitness in a mixed-mating population of the yellow monkeyflower, Mimulus guttatus (Phrymaceae). Female fitness was strongly pollen-limited, with supplementally pollinated plants setting 37% more seeds than open-pollinated individuals. Strong positive selection was found on flower length, weak positive selection on flower width : length ratio and no selection on stigma-anther distance in both open-pollinated and supplementally pollinated treatments. By contrast, flowers with relatively narrow corollas and low stigma-anther distances were favored in the pollinator exclusion treatment. These results provide mixed support for the idea that pollen limitation intensifies selection on floral characters. Despite strong phenotypic selection, natural pollen limitation did not mediate selection on characters associated with either pollinator attraction or self-fertilization. However, the novel pattern of selection on severely pollen-limited plants suggests that reproductive assurance against pollinator loss may have been directly involved in the floral evolution of closely related selfing taxa.     

The benefits of bathing buds: water calyces protect flowers from a microlepidopteran herbivore

Protective floral structures may evolve in response to the negative effects of floral herbivores. For example, water calyces--liquid-filled, cup-like structures resulting from the fusion of sepals--may reduce floral herbivory by submerging buds during their development. Our observations of a water-calyx plant, Chrysothemis friedrichsthaliana (Gesneriaceae), revealed that buds were frequently attacked by ovipositing moths (Alucitidae), whose larvae consumed anthers and stigmas before corollas opened. Almost 25% of per-plant flower production was destroyed by alucitid larvae over two seasons, far exceeding the losses to all other floral herbivores combined. Experimental manipulation of water levels in calyces showed that a liquid barrier over buds halved per-flower alucitid egg deposition and subsequent herbivory, relative to buds in calyces without water. Thus, C. friedrichsthaliana's water calyx helps protect buds from a highly detrimental floral herbivore. Our findings support claims that sepal morphology is largely influenced by selection to reduce floral herbivory, and that these pressures can result in novel morphological adaptations.     

高阶作用对植物-传粉者-植食动物集合群落续存的影响

高阶作用通常指一个物种对另外两个物种之间相互作用强度的影响,对物种共存、群落构建及生物多样性具有重要影响。在集合种群水平上考虑了植食动物对动植物传粉关系造成的高阶作用,以及植食动物对传粉者的间接作用。通过分析基本生态过程,建立植物-传粉者-植食动物的集合群落模型,模型清楚地展示高阶作用和间接作用,可以用来研究它们对集合群落稳定性和续存的影响。结果表明：(1)互惠关系在集合群落尺度上会引起双稳态现象,说明了群落动态对初始条件的依赖性;(2)正高阶作用能够扩大集合群落双稳态的参数范围,负高阶作用和间接作用缩小它的参数范围,但都不会从本质上改变双稳态现象;(3)正高阶作用能够降低集合群落的灭绝阈值,增加集合群落稳定时的占有率,有利于集合群落续存,而负高阶作用和间接作用不利于续存。研究结果说明高阶和间接作用对调节多物种系统动态和物种共存具有重要作用。     

Growth at elevated CO2 concentrations leads to modified profiles of secondary metabolites in tobacco cv. SamsunNN and to increased resistance against infection with potato virus Y

The effect of elevated CO2 concentrations on the levels of secondary metabolites was investigated in tobacco plants grown under two nitrogen supply (5 and 8 mM NH4NO3) and CO2 conditions (350 and 1000 p.p.m.) each. High CO2 resulted in a dramatic increase of phenylpropanoids in the leaves, including the major carbon-rich compound chlorogenic acid (CGA) and the coumarins scopolin and scopoletin at both nitrogen fertilizations. This was accompanied by increased PAL activity in leaves and roots, which was even higher at the lower nitrogen supply. Hardly any change was observed for the structural phenolic polymer lignin and the sesquiterpenoid capsidiol. In contrast, elevated CO2 led to clearly decreased levels of the main nitrogen-rich constituent nicotine at the lower N-supply (5 mM NH4NO3) but not when plants were grown at the higher N-supply (8 mM NH4NO3). Inoculation experiments with potato virus Y (PVY) were used to evaluate possible ecological consequences of elevated CO2. The titre of viral coat-protein was markedly reduced in leaves under these conditions at both nitrogen levels. Since PR-gene expression and free salicylic acid (SA) levels remained unchanged at elevated CO2, we suggest that the accumulation of phenylpropanoids, for example, the major compound CGA and the coumarins scopolin and scopoletin may result in an earlier confinement of the virus at high CO2. Based on our results two final conclusions emerge. First, elevated CO2 leads to a shift in secondary metabolite composition that is dependent on the availability of nitrogen. Second, changes in the pool of secondary metabolites have important consequences for plant-pathogen interactions as shown for PVY as a test organism.     

DO TRADE‐OFFS HAVE EXPLANATORY POWER FOR THE EVOLUTION OF ORGANISMAL INTERACTIONS?

The concept of a trade-off has long played a prominent role in understanding the evolution of organismal interactions such as mutualism, parasitism, and competition. Given the complexity inherent to interactions between different evolutionary entities, ecological factors may especially limit the power of trade-off models to predict evolutionary change. Here, we use four case studies to examine the importance of ecological context for the study of trade-offs in organismal interactions: (1) resource-based mutualisms, (2) parasite transmission and virulence, (3) plant biological invasions, and (4) host range evolution in parasites and parasitoids. In the first two case studies, mechanistic trade-off models have long provided a strong theoretical framework but face the challenge of testing assumptions under ecologically realistic conditions. Work under the second two case studies often has a strong ecological grounding, but faces challenges in identifying or quantifying the underlying genetic mechanism of the trade-off. Attention is given to recent studies that have bridged the gap between evolutionary mechanism and ecological realism. Finally, we explore the distinction between ecological factors that mask the underlying evolutionary trade-offs, and factors that actually change the trade-off relationship between fitness-related traits important to organismal interactions.