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1.
Organic solar cells that are free of burn‐in, the commonly observed rapid performance loss under light, are presented. The solar cells are based on poly(3‐hexylthiophene) (P3HT) with varying molecular weights and a nonfullerene acceptor (rhodanine‐benzothiadiazole‐coupled indacenodithiophene, IDTBR) and are fabricated in air. P3HT:IDTBR solar cells light‐soaked over the course of 2000 h lose about 5% of power conversion efficiency (PCE), in stark contrast to [6,6]‐Phenyl C61 butyric acid methyl ester (PCBM)‐based solar cells whose PCE shows a burn‐in that extends over several hundreds of hours and levels off at a loss of ≈34%. Replacing PCBM with IDTBR prevents short‐circuit current losses due to fullerene dimerization and inhibits disorder‐induced open‐circuit voltage losses, indicating a very robust device operation that is insensitive to defect states. Small losses in fill factor over time are proposed to originate from polymer or interface defects. Finally, the combination of enhanced efficiency and stability in P3HT:IDTBR increases the lifetime energy yield by more than a factor of 10 when compared with the same type of devices using a fullerene‐based acceptor instead.  相似文献   
2.
Pattern formation occurs in a wide range of biological systems. This pattern formation can occur in mathematical models because of diffusion-driven instability or due to the interaction between reaction, diffusion, and chemotaxis. In this paper, we investigate the spatial pattern formation of attack clusters in a system for Mountain Pine Beetle. The pattern formation (aggregation) of the Mountain Pine Beetle in order to attack susceptible trees is crucial for their survival and reproduction. We use a reaction-diffusion equation with chemotaxis to model the interaction between Mountain Pine Beetle, Mountain Pine Beetle pheromones, and susceptible trees. Mathematical analysis is utilized to discover the spacing in-between beetle attacks on the susceptible landscape. The model predictions are verified by analysing aerial detection survey data of Mountain Pine Beetle Attack from the Sawtooth National Recreation Area. We find that the distance between Mountain Pine Beetle attack clusters predicted by our model closely corresponds to the observed attack data in the Sawtooth National Recreation Area. These results clarify the spatial mechanisms controlling the transition from incipient to epidemic populations and may lead to control measures which protect forests from Mountain Pine Beetle outbreak.  相似文献   
3.
The classical model of colony dynamics developed by Macevicz and Oster predicts that optimal colony fitness in annual eusocial insects is achieved by a bang-bang strategy of reproduction: exclusive production of workers (ergonomic phase) followed by exclusive production of sexuals (reproductive phase). We propose an alternative model that assumes colony development in discrete broods and a limited overall investment potential of the queen. Based on the costs for producing eggs, workers, and sexuals and efficiency of individuals we predict the optimal number of workers and sexuals in the colony for each brood of the colony cycle that maximizes overall colony fitness. To link our model assumptions to the real world we chose model parameters according to field data of the halictid bee Lasioglossum malachurum. However, our model is representative of a large number of species with an annual life cycle and with discrete broods. Our model shows that the optimal partitioning of resources, i.e. the optimal workers/sexuals ratio depends on rearing cost for sexuals as well as productivity of workers but not on the queens’ total investment, egg cost, or rearing cost for workers. In complete accordance to Macevicz and Oster we predict a bang-bang reproduction strategy despite the differences in the basic assumptions. Potential deviations from this strategy and transitions from social to solitary breeding are discussed in the framework of our model. Received 31 October 2006; revised 29 March 2007; accepted 17 April 2007.  相似文献   
4.
Exocrine glands play an important role in maintaining the integrity of colonies of social Hymenoptera. The postpharyngeal gland (PPG) of ants is crucial for the generation of a nest odour that enables nestmate recognition. The evolutionary history of this gland is unknown and it was thought to be restricted to ants. Here we describe an exocrine head gland in females of a solitary crabronid wasp, the European beewolf, Philanthus triangulum, that resembles the PPG of ants in many respects. The newly described gland has the same location and the same glove like shape as in ants, and it also has a monolayered epithelium with similar ultrastructure. Unlike in ants, the epithelium bears hairs that reach into the lumen of the gland. Although the PPG of beewolves serves a completely different function it is also associated to an allogrooming behaviour as in ants. Based on these morphological and behavioural similarities as well as similarities in the chemical composition of the content of the PPG of both taxa, we hypothesise that the PPGs of ants and beewolves have a common evolutionary origin. Thus, our results suggest that the PPG in ants might not have evolved in response to social requirements but might have already existed in solitary predecessors.  相似文献   
5.
Insects engage in symbiotic associations with a large diversity of beneficial microorganisms. While the majority of well-studied symbioses have a nutritional basis, several cases are known in which bacteria protect their host from pathogen infestation. Solitary wasps of the genera Philanthus and Trachypus (beewolves; Hymenoptera, Crabronidae) cultivate the actinomycete "Candidatus Streptomyces philanthi" in specialized antennal gland reservoirs. The symbionts are transferred to the larval cocoon, where they provide protection against pathogenic fungi by producing at least nine different antibiotics. Here we investigated the closest relatives of Philanthus and Trachypus, the rare genus Philanthinus, for the presence of antennal gland reservoirs and symbiotic streptomycetes. Molecular analyses identified "Ca. Streptomyces philanthi" in reservoirs of Philanthinus quattuordecimpunctatus. Phylogenies based on the 16S rRNA gene suggest that P. quattuordecimpunctatus may have acquired "Ca. Streptomyces philanthi" by horizontal transfer from other beewolf species. In histological sections and three-dimensional reconstructions, the antennal gland reservoirs were found to occupy six antennal segments (as opposed to only five in Philanthus and Trachypus) and to be structurally less complex than those of the evolutionarily more derived genera of beewolves. The presence of "Ca. Streptomyces philanthi" in antennal glands of Philanthinus indicates that the symbiosis between beewolves and Streptomyces bacteria is much older than previously thought. It probably evolved along the branch leading to the monophyletic tribe Philanthini, as it seems to be confined to the genera Philanthus, Trachypus, and Philanthinus, which together comprise 172 described species of solitary wasps.  相似文献   
6.
Through four spatially explicit models, we investigate how habitat fragmentation affects cyclic predator–prey population dynamics. We use a Partial Differential Equation (PDE) framework to describe the dispersal of predators and prey in a heterogeneous landscape made of high quality and low quality habitat patches, subject to increasing fragmentation through habitat separation and/or habitat loss. Our results show that habitat fragmentation decreases the amplitude of the predator–prey population cycles while average population density is not as strongly affected in general. Beyond these simple trends however, the four models show differing responses to fragmentation, indicating that when making predictions about population survival and persistence in the face of habitat fragmentation, the choice of model is important. Our results may inform conservation efforts in fragmented habitats for cyclic species such as the snowshoe hare and Canada lynx. Electronic Supplementary Material  The online version of this article () contains supplementary material, which is available to authorised users.  相似文献   
7.
Factors affecting body size and fat content in a digger wasp   总被引:1,自引:0,他引:1  
Erhard Strohm 《Oecologia》2000,123(2):184-191
Body size is one of the most important life history traits. In mass-provisioning solitary Hymenoptera, the maximum attainable adult size is not under the control of the larva but is limited by the amount of resources provided by the mother. I investigated the effect of the amount of different maternal resources and potentially interfering abiotic (temperature) and biotic (fungus infestation) factors on offspring body size and fat reserves in a solitary digger wasp, the European beewolf, Philanthus triangulum F. (Hymenoptera, Sphecidae). Females provide different resources for their progeny that might influence progeny size (egg, brood cell, and paralysed honey-bees as food). The number of bees provisioned explained the largest proportion of variation in cocoon length. With an increasing number of bees (one to four), progeny gained less weight per bee. Relative fat content increased with size. With a given number of bees, males were smaller than females. The duration of the feeding period was independent of the number of bees in a brood cell but decreased with increasing ambient temperatures (20, 25, 30°C). Cocoon size was influenced by temperature but the effect was not uniform. Cocoons from brood cells containing two and three bees were larger at 25°C than at 20°C; those at 30°C did not differ from those at either lower temperature. However, in brood cells containing one bee, cocoon length was independent of temperature. Sublethal levels of fungus infestation may have a small negative effect on cocoon size. Different temperatures during hibernation (8 vs 13°C) did not affect the size or fat content of emerging adults. These results on a mass-provisioning hunting wasp are compared with the well-studied herbivorous insects. Received: 12 April 1999 / Accepted: 3 December 1999  相似文献   
8.
9.
Internode stem fragments of the poplar hybrid Populus tremula x Populus alba were transformed with a bacterial gene (gshl) for [gamma]-glutamylcysteine synthetase ([gamma]-ECS) targeted to the cytosol. Lines overexpressing [gamma]-ECS were identified by northern analysis, and the transformant with the highest enzyme activity was used to investigate the control of glutathione synthesis. Whereas foliar [gamma]-ECS activity was below the limit of detection in untransformed plants, activities of up to 8.7 nmol mg-1 protein min-1 were found in the transformant, in which the foliar contents of [gamma]-glutamylcysteine ([gamma]-EC) and glutathione were increased approximately 10- and 3-fold, respectively, without affecting either the reduction state of the glutathione pool or the foliar cysteine content. A supply of exogenous cysteine to leaf discs increased the glutathione content from both transformed and untransformed poplars, and caused the [gamma]-EC content of the transformant discs to increase still further. The following conclusions are drawn: (a) the native [gamma]-ECS of untransformed poplars exists in quantities that are limiting for foliar glutathione synthesis; (b) foliar glutathione synthesis in untransformed poplars is limited by cysteine availability; (c) in the transformant interactions between glutathione synthesis and cysteine synthesis operate to sustain the increased formation of [gamma]-EC and glutathione; and (d) the foliar glutathione content of the transformant is restricted by cysteine availability and by the activity of glutathione synthetase.  相似文献   
10.
Untransformed hybrid poplar (Populus tremula x P. alba) and transgenic lines overexpressing glutathione synthetase (GshS) in the cytosol (200-300-fold) or glutathione reductase (GR) either in the cytosol 5-fold) or in the chloroplast (150-200-fold) were exposed to 0 (control), 100, 200 or 300 nl l-1 ozone for 3 d for 7 h d-1. Following acute ozone stress treatments, wild-type and transgenic poplar suffered from visible foliar injury consisting of dark brown necrotic lesions on the laminae. Necrotic lesions were sharply separated from photosynthetically active cells by a band of red-violet discoloured cell lines showing yellow autofluorescence by blue light, and blue autofluorescence by UV-light excitation. When plants were exposed to 100 nl l-1 ozone, leaf injury was in general negligible, but when 200 and 300 nl l-1 ozone was applied, in both untransformed poplar and transgenic lines overexpressing GshS or GR up to 60% and 80%, respectively, visible injury developed on mature leaves. The mean percentage of injured leaf area amounted to 20-30% (200 nl l-1) and 40-60% (300 nl l-1). Irrespective of transformation, young leaves of poplar trees were only slightly affected by ozone treatments. In support of these observations, net CO2 assimilation rates of mature leaves were decreased by up to 65% (300 nl l-1 ozone) in wild-type and transformed poplar, whereas net photosynthesis of young leaves remained unaffected even under severe stress conditions. Leaf conductance was significantly decreased by all ozone treatments, but was in the same range in young and mature leaves, and in wild-type and transformed poplar, pre- and post-exposure to ozone. It can therefore be assumed that the ozone doses effectively taken up into the leaf tissue were not dependent on leaf development and that the strength of the ozone stress exerted was similar in all types of poplar trees investigated in this study.From these data it is concluded that: (i) elevated foliar activities of glutathione synthetase or glutathione reductase alone are not sufficient to improve tolerance of hybrid poplar to acute ozone stress, and (ii) the sensitivity of poplar leaves to acute ozone stress is controlled by unknown factors closely related to leaf development rather than by foliar activities of glutathione synthetase and glutathione reductase, or leaf conductance.  相似文献   
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