Selection of large host plants for oviposition by a monophagous leaf beetle: nutritional quality or enemy‐free space?

Abstract.  1. Oviposition site selection is crucial for the reproductive success of herbivorous insects. According to the preference–performance hypothesis, females should oviposit on host plants that enhance the performance of their offspring. More specifically, the plant vigour hypothesis predicts that females should prefer large and vigorously growing host plants for oviposition and that larvae should perform best on these plants.
2. The present study examined whether females of the monophagous leaf beetle Cassida canaliculata Laich. (Coleoptera: Chrysomelidae) prefer to oviposit on large host plant individuals of the meadow clary and whether large host plants are of higher nutritional quality than small host plants. Subsequently, it was tested whether the female preference correlates with offspring performance and survival.
3. In the field, females preferred large host plant individuals for oviposition and host plant quality, i.e. leaf nitrogen content, was significantly higher in leaves of large than of small host plants.
4. In the laboratory, larval development time was shorter on leaves of large host plant individuals than on small host plant individuals, but this could not be shown in the field.
5. However, a predator-exclusion experiment in the field resulted in a higher survival of larvae on large host plants than on small host plants when all predators had free access to the plants. On caged host plants there was no difference in survival of larvae between plant size categories.
6. It is concluded that females of C. canaliculata select oviposition sites that enhance both performance and survival of their offspring, which meets the predictions of the plant vigour hypothesis.     

Multiannual effects of induced plant defenses: Are defended plants good or bad neighbors?

Defenses induced by herbivore feeding or phytohormones such as methyl jasmonate (MeJA) can affect growth, reproduction, and herbivory, not only on the affected individual but also in its neighboring plants. Here, we report multiannual defense, growth, and reproductive responses of MeJA‐treated bilberry (Vaccinium myrtillus) and neighboring ramets. In a boreal forest in western Norway, we treated bilberry ramets with MeJA and water (control) and measured responses over three consecutive years. We observed the treatment effects on variables associated with herbivory, growth, and reproduction in the MeJA‐treated and untreated ramet and neighboring ramets distanced from 10 to 500 cm. MeJA‐treated ramets had fewer grazed leaves and browsed shoots compared to control, with higher effects in 2014 and 2015, respectively. In 2013, growth of control ramets was greater than MeJA‐treated ramets. However, MeJA‐treated ramets had more flowers and berries than control ramets 2 years after the treatment. The level of insect and mammalian herbivory was also lower in untreated neighboring ramets distanced 10–150 cm and, consistent with responses of MeJA‐treated ramets, the stronger effect was also one and 2 years delayed, respectively. The same neighboring ramets had fewer flowers and berries than untreated ramets, indicating a trade‐off between defense and reproduction. Although plant–plant effects were observed across all years, the strength varied by the distance between the MeJA‐treated ramets and its untreated neighbors. We document that induced defense in bilberry reduces both insect and mammalian herbivory, as well as growth, over multiple seasons. The defense responses occurred in a delayed manner with strongest effects one and 2 years after the induction. Additionally, our results indicate defense signaling between MeJA‐treated ramets and untreated neighbors. In summary, this study shows that induced defenses are important ecological strategies not only for the induced individual plant but also for neighboring plants across multiple years in boreal forests.     

Experimental effects of habitat fragmentation on rove beetles and ants: patch area or edge?

The effects of habitat fragmentation may include the loss of species from isolated fragments or changes in species abundances among habitats that differ in area, structure, or edge characteristics. We measured the species richness and abundance of ground‐dwelling insects in a 1.14‐ha old field that was mowed to produce patches of unmowed vegetation which differed in size, degree of isolation, and the amount of habitat edge. Four treatments – ranging from unfragmented (169‐m²) to highly fragmented (1‐m²) patches – were replicated four times in a Latin square design, and insects were sampled twice during 1995 using 177 pitfall traps. Species richness showed a non‐monotonic response to fragmentation, with the fewest species occurring in the slightly fragmented treatment. Responses of rove beetles and ants, the most species‐rich and abundant taxa, respectively, were similar to the overall insect community but ants had a stronger and more consistent treatment effect in both sample months. Ordinations of ant and rove‐beetle assemblages using nonmetric multidimensional scaling showed that the slightly fragmented treatment differed from other treatments in species occurrence and abundance. The lower species richness in the slightly fragmented treatment was primarily due to a subset of ant and rove beetle species that showed a lower abundance than in other treatments, possibly because this treatment had the greatest amount of habitat edge. We hypothesize that the non‐monotonic species response to fragmentation was due to the differential effects of habitat edge on species movements across the habitat boundary between unmowed patches and mowed areas. A greater effect due to the amount of habitat edge rather than total patch area, at least among the range of patch sizes studied, suggests that the length of habitat edge may be quite important to the distribution and abundance of ground‐dwelling animals in fragmented habitats.     

Avoidance of roads and selection for recent cutovers by threatened caribou: fitness-rewarding or maladaptive behaviour?

The impact of anthropogenic disturbance on the fitness of prey should depend on the relative effect of human activities on different trophic levels. This verification remains rare, however, especially for large animals. We investigated the functional link between habitat selection of female caribou (Rangifer tarandus) and the survival of their calves, a fitness correlate. This top-down controlled population of the threatened forest-dwelling caribou inhabits a managed forest occupied by wolves (Canis lupus) and black bears (Ursus americanus). Sixty-one per cent of calves died from bear predation within two months following their birth. Variation in habitat selection tactics among mothers resulted in different mortality risks for their calves. When calves occupied areas with few deciduous trees, they were more likely to die from predation if the local road density was high. Although caribou are typically associated with pristine forests, females selected recent cutovers without negative impact on calf survival. This selection became detrimental, however, as regeneration took place in harvested stands owing to increased bear predation. We demonstrate that human disturbance has asymmetrical consequences on the trophic levels of a food web involving multiple large mammals, which resulted in habitat selection tactics with a greater short-term fitness payoff and, therefore, with higher evolutionary opportunity.     

Habitat difference in abundance of willow leaf beetle Phratora vulgatissima (Coleoptera: Chrysomelidae): plant quality or natural enemies?

Herbivorous insects are influenced by both 'bottom-up' forces mediated through host plants and 'top-down' forces from natural enemies. Few studies have tried to evaluate the relative importance of the two forces in determining the abundance of insects. The leaf beetle Phratora vulgatissima Linnaeus sometimes occurs at high densities and severely damages the willow Salix cinerea in forest habitats. For willows growing in open agricultural landscapes (farmland S. cinerea), the leaf beetle generally occurs at low densities and plants receive little damage. The purpose of the present study was to evaluate the relative importance of host plant quality and natural enemies behind the observed difference in P. vulgatissima abundance. Female egg-laying and larval performance (growth and survival) were studied on caged willow branches in the field to investigate if plant quality differs between S. cinerea trees growing in forest and farmland habitats. The survival of eggs exposed to natural enemies was examined to see if predation could explain the low abundance of leaf beetles on farmland willows. The results indicated no difference in plant quality; female egg laying and larval performance did not differ between the forest and the farmland. However, heteropteran predators (true bugs) were more abundant, and the survival of eggs was lower, on plants in the farmland habitat than in the forest habitat. The data suggest that the low abundance of P. vulgatissima on farmland willows could not be explained by a poor quality of plants, but more likely by high predation from heteropterans.     

Inhibition of growth,and effects on nutrient uptake of arctic graminoids by leaf extracts — allelopathy or resource competition between plants and microbes?

Previous research has shown that plant extracts, e.g. from boreal dwarf shrubs and trees, can cause reduced growth of neighbouring plants: an effect known as allelopathy. To examine whether arctic and subarctic plants could also be affected by leaching of phytochemicals, we added extracts from the commonly occurring arctic dwarf shrubs Cassiope tetragona and Empetrum hermaphroditum, and from mountain birch, Betula pubescens ssp. tortuosa to three graminoid species, Carex bigelowii, Festuca vivipara and Luzula arcuata, grown in previously sterilized or non-sterilized arctic soils. The graminoids in non-sterilized soil grew more slowly than those in sterilized soil. Excised roots of the plants in non-sterilized soil had higher uptake rate of labelled P than those in sterilized soil, demonstrating larger nutrient deficiency. The difference in growth rate was probably caused by higher nutrient availability for plants in soils in which the microbial biomass was killed after soil sterilization. The dwarf shrub extracts contained low amounts of inorganic N and P and medium high amounts of carbohydrates. Betula extracts contained somewhat higher levels of N and much higher levels of P and carbohydrates. Addition of leaf extracts to the strongly nutrient limited graminoids in non-sterilized soil tended to reduce growth, whereas in the less nutrient limited sterilized soil it caused strong growth decline. Furthermore, the N and P uptake by excised roots of plants grown in both types of soil was high if extracts from the dwarf shrubs (with low P and N concentrations) had been added, whereas the P uptake declined but the N uptake increased after addition of the P-rich Betula extract. In contrast to the adverse extract effects on plants, soil microbial respiration and soil fungal biomass (ergosterol) was generally stimulated, most strongly after addition of the Betula extract. Although we cannot exclude the possibility that the reduced plant growth and the concomitant stimulation of microbial activity were caused by phytochemicals, we believe that this was more likely due to labile carbon in the extracts which stimulated microbial biomass and activity. As a result microbial uptake increased, thereby depleting the plant available pool of N and P, or, for the P-rich Betula extract, depleting soil inorganic N alone, to the extent of reducing plant growth. This chain of events is supported by the negative correlation between plant growth and sugar content in the three added extracts, and the positive correlation between microbial activity, fungal biomass production and sugar content, and are known reactions when labile carbon is added to nutrient deficient soils.     

Bottom-up control of carabid beetle communities in early successional wetlands: mediated by vegetation structure or plant diversity?

Two hypotheses of bottom-up control that predict that the species richness of Carabidae will depend either on the taxonomic diversity of plants ("taxonomic diversity hypothesis") or on the structural heterogeneity of the vegetation ("structural heterogeneity hypothesis") were tested. Plant species were classified into nine plant structural groups through cluster analysis of morphological traits (e.g. total height) at 30 early successional temporary wetlands in the east-German agricultural landscape. In a linear regression analysis, the heterogeneity of vegetation structures explained 55% of the variation in carabid beetle diversity. According to a partial correlation analysis, plant taxonomic diversity did not have a significant effect, consistent with the "structural heterogeneity hypothesis," and contradicting previous studies which concluded that plant taxonomic diversity would be the most important factor in early successional habitats. An experimental study was used to test hypotheses on the processes underlying this bottom-up control by vegetation structure: the "hunting efficiency hypothesis," the "enemy-free space hypothesis," and the "microhabitat specialization hypothesis." The composition of plant structural groups in 15 vegetation plots (1 m(2)) was manipulated, creating a gradient from dense vegetation to open plots. Subsequent pitfall catches revealed significant differences in the activity-abundances of the carabid species. Large species preferred dense vegetation plots, consistent with the enemy-free space hypothesis that large species are more vulnerable to predation on the open plots and prefer dense vegetation to escape from natural enemies. The results indicate that bottom-up control is not mediated only by plant taxonomic or functional group diversity and that vegetation structures may be more important than previously suggested.     

Stomatal malfunctioning under low VPD conditions: induced by alterations in stomatal morphology and leaf anatomy or in the ABA signaling?

Exposing plants to low VPD reduces leaf capacity to maintain adequate water status thereafter. To find the impact of VPD on functioning of stomata, stomatal morphology and leaf anatomy, fava bean plants were grown at low (L, 0.23 kPa) or moderate (M, 1.17 kPa) VPDs and some plants that developed their leaves at moderate VPD were then transferred for 4 days to low VPD (M→L). Part of the M→L‐plants were sprayed with ABA (abscisic acid) during exposure to L. L‐plants showed bigger stomata, larger pore area, thinner leaves and less spongy cells compared with M‐plants. Stomatal morphology (except aperture) and leaf anatomy of the M→L‐plants were almost similar to the M‐plants, while their transpiration rate and stomatal conductance were identical to that of L‐plants. The stomatal response to ABA was lost in L‐plants, but also after 1‐day exposure of M‐plants to low VPD. The level of foliar ABA sharply decreased within 1‐day exposure to L, while the level of ABA‐GE (ABA‐glucose ester) was not affected. Spraying ABA during the exposure to L prevented loss of stomatal closing response thereafter. The effect of low VPD was largely depending on exposure time: the stomatal responsiveness to ABA was lost after 1‐day exposure to low VPD, while the responsiveness to desiccation was gradually lost during 4‐day exposure to low VPD. Leaf anatomical and stomatal morphological alterations due to low VPD were not the main cause of loss of stomatal closure response to closing stimuli.     

Mechanisms of chlorophyll fluorescence revisited: Prompt or delayed emission from photosystem II with closed reaction centers?

This paper proposes a model which correlates the exciton decay kinetics observed in picosecond fluorescence studies with the primary processes of charge separation in the reaction center of photosystem II. We conclude that the experimental results from green algae and chloroplasts from higher plants are inconsistent with the concept that delayed luminescence after charge recombination should account for the long-lived (approx. 2 ns) fluorescence decay component of closed photosystem II centers. Instead, we show that the experimental data are in agreement with a model in which the long-lived fluorescence is also prompt fluorescence. The model suggests furthermore that the rate constant of primary charge separation is regulated by the oxidation state of the quinone acceptor Q_A.     

Avoidance of aposematic prey in European tits (Paridae): learned or innate?

Predators may either learn to avoid aposematic prey or may avoidit because of an innate bias. Learned as well as innate avoidancehas been observed in birds, but the existing evidence is basedon experiments with rather few unrelated model species. We comparedthe origin of avoidance in European species of tits (Paridae).First, we tested whether wild-caught birds (blue tits, greattits, crested tits, coal tits, willow tits, and marsh tits)avoid aposematic (red and black) adult firebugs Pyrrhocorisapterus (Heteroptera) more than nonaposematic (brown painted)ones. Larger proportion of birds avoided aposematic than brown-paintedfirebugs in majority of species (except coal tits). Second,we tested whether naive hand-reared birds of 4 species (bluetits, great tits, crested tits, and coal tits) attack or avoidaposematic and nonaposematic firebugs, both novel for them.Behavior of the naive blue tits and coal tits was similar tothat of the wild-caught birds; majority of them did not attackthe firebugs. Contrastingly, the naive great tits and crestedtits behaved differently than the wild-caught conspecific adults;majority of the wild-caught birds avoided the aposematic firebugs,whereas the naive birds usually did not show any initial avoidanceand had to learn to avoid the aposematic prey. Our results showthat the origin of avoidance may be different even in closelyrelated species. Because blue tits and coal tits avoided notonly aposematic firebugs but also their brown-painted form,we interpret their behavior as innate neophobia rather thaninnate bias against the warning coloration.     

Insulin resistance in the liver: Deficiency or excess of insulin?

In insulin-resistant states (obesity, pre-diabetes, and type 2 diabetes), hepatic production of glucose and lipid synthesis are heightened in concert, implying that insulin deficiency and insulin excess coexists in this setting. The fact that insulin may be inadequate or excessive at any one point in differing organs and tissues has many biologic ramifications. In this context the concept of metabolic compartmentalization in the liver is offered herein as one perspective of this paradox. In particular, we focus on the hypothesis that insulin resistance accentuates differences in periportal and perivenous hepatocytes, namely periportal glucose production and perivenous lipid synthesis. Subsequently, excessive production of glucose and accumulation of lipids could be expected in the livers of patients with obesity and insulin resistance. Overall, in this review, we provide our integrative perspective regarding how excessive production of glucose in periportal hepatocytes and accumulation of lipids in perivenous hepatocytes interact in insulin resistant states.     

The positive effects of negative interactions: Can avoidance of competitors or predators increase resource sampling by prey?

Spatial overlap between predators and prey is key to predicting their interaction strength and population dynamics. We constructed a spatially-explicit simulation model to explore how predator and prey behavioral traits and patterns of resource distribution influence spatial overlap between predators, prey, and prey resources. Predator and prey spatial association primarily followed the ideal free distribution. Departures from this model were intriguing, especially from the interactions of predator and prey behavior. When prey weakly avoided conspecifics, they associated more highly with resources when predators were present. Predators increased the rate of prey movement between patches, which increased their ability to sample their environment and aggregate in patches with high resources. When prey strongly avoided each other, predators decreased prey association with resources. That is, an increased rate of prey movement increased the probability that prey would interact and avoid each other without regard to the distribution of resources. More generally, a more highly clumped distribution of resources acted as a spatial anchor that generally increased prey, predator, and resource association. Prey tended to congregate with resources and predators generally congregated with prey.     

Diel patterns of leaf and root growth: endogenous rhythmicity or environmental response?

Plants are sessile organisms forced to adjust to their surrounding environment. In a single plant the photoautotrophic shoot is exposed to pronounced environmental variations recurring in a day-night 24?h (diel) cycle, whereas the heterotrophic root grows in a temporally less fluctuating environment. The contrasting habitats of shoots and roots are reflected in different diel growth patterns and their responsiveness to environmental stimuli. Differences between diel leaf growth patterns of mono- and dicotyledonous plants correspond to their different organization and placement of growth zones. In monocots, heterotrophic growth zones are organized linearly and protected from the environment by sheaths of older leaves. In contrast, photosynthetically active growth zones of dicot leaves are exposed directly to the environment and show characteristic, species-specific diel growth patterns. It is hypothesized that the different exposure to environmental constraints and simultaneously the sink/source status of the growing organs may have induced distinct endogenous control of diel growth patterns in roots and leaves of monocot and dicot plants. Confronted by strong temporal fluctuations in environment, the circadian clock may facilitate robust intrinsic control of leaf growth in dicot plants.     

Is preventative, concurrent management of the soybean aphid (Hemiptera: Aphididae) and bean leaf beetle (Coleoptera: Chrysomelidae) possible?

In Iowa, the management of insect pests in soybean, Glycine max (L.) Merr., has been complicated by the arrival of the invasive species soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), and occasional outbreaks of bean leaf beetle, Cerotoma trifurcata (F?rster) (Coleoptera: Chrysomelidae), populations leading to economic losses. Several insecticide programs designed to reduce abundance of the overwintered and first generation C. trifurcata and the incidence of bean pod mottle virus were evaluated over 3 yr (2004-2006) for their impacts on A. glycines populations, at three locations in Iowa (Floyd, Lucas, and Story counties). There was no significant overlap of either overwintered (early May) or the first (early July) generations of C. trifurcata with A. glycines, because aphids were first detected in June and they did not reach economically damaging levels until August, if at all. During this study, insecticides targeting the overwintered population or the first generation of C. trifurcata provided a limited impact on A. glycines populations compared with untreated controls, and they did not prevent economic populations from occurring. Furthermore, the highest populations of A. glycines were frequently observed when a low rate of lambda-cyhalothrin (178 ml/ha) was applied targeting the overwintered population of C. trifurcata. Soybean yields were not protected by any of the insecticide treatments. Our results indicate that the use of either early season foliar or seed-applied insecticides for C. trifurcata management is of limited value for A. glycines management.     

Mixed effects of effluents from a wastewater treatment plant on river ecosystem metabolism: subsidy or stress?

相似文献   

Physiological effects of dominance hierarchies: laboratory artefacts or natural phenomena?

Studies of fish behaviour have demonstrated the existence of social interactions that result in dominance hierarchies. In environments in which resources, such as food, shelter and mates, are limited, social competition results in some fish becoming dominant and occupying the most profitable positions. This behaviour has been observed in natural environments and also in many laboratory‐based experiments. When two fish have been confined in a small tank, one of them usually has exhibited behaviour that suggests it is dominant over the other submissive animal. Physiological consequences of social interaction can be seen in both dominants and subordinates but are more extreme in the subordinate. However, this scenario is without doubt an artificial situation. Fewer experiments have been conducted using laboratory experiments that are more socially and physically complex than those experienced by dyads in tanks. In simple fluvial tanks, through which water is recirculated, the physiological responses of fish to social competition have generally been qualitatively similar to those recorded among dyads. However, when environmental disturbances, complex resource distributions, increase in water flushing, presence of predators and competing species of fish have been included in experimen‐tal designs, there have been fewer, diminished or no physiological dierences between dominant and subordinate fish. There have been very few studies of physiology in relation to dominance in natural habitats, and those that have been conducted suggest that under some circumstances hierarchies may cause less intense physiological responses than have been suggested based on results of laboratory studies in simple environments. Possible reasons for these variations are discussed. The need is identified for a well structured experimental approach to the investi‐gation of the causes and consequences of hierarchies if the ecology of wild fish is to be modelled eectively based on physiological processes. It is also suggested that the further development and application of techniques for monitoring physiologies of fish in the wild is important.     

Mating interaction of the Japanese horned beetle Trypoxylus dichotomus septentrionalis: does male-excluding behavior induce female resistance?

Female resistance to male mating is thought to have developed as a mechanism to avoid multiple matings or to allow the choice of good quality males. Detailed mating behavior of the Japanese horned beetle Trypoxylus dichotomus septentrionalis (Kono) was examined under natural conditions to clarify the function of female resistance to mating. When a male recognized the presence of a female at the same feeding spot, it immediately began to court and mount the female and attempted to insert its genitalia. During the courtship, females performed intense resistance behavior against the mating, regardless of whether the female would eventually accept males or not. In T. dichotomus septentrionalis, it was observed that female resistance to mating did not occur for reasons of precopulatory mate choice or avoidance of multiple matings; however, additional studies on postcopulatory mate choice are needed. After copulation, males usually tried to keep females away from the sap site. Because of males' excluding behavior, females were able to stay at the sap site for feeding only when they were resisting or copulating. Females that showed resistance behavior before copulation stayed at the sap site 1.56 times longer than females that did not show the resistance behavior. Female resistance behavior in T. dichotomus septentrionalis is thus considered a tactic for prolonging their feeding duration, which is reduced by male-excluding behavior after mating.     

Paradoxes of tumour complexity: somatic selection,vulnerability by design,or infectious aetiology?

The aetiology of cancer involves intricate cellular and molecular mechanisms that apparently emerge on the short timescale of a single lifetime. Some of these traits are remarkable not only for their complexity, but also because it is hard to conceive selection pressures that would favour their evolution within the local competitive microenvironment of the tumour. Examples include ‘niche construction’ (re‐programming of tumour‐specific target sites) to create permissive conditions for distant metastases; long‐range feedback loops of tumour growth; and remarkably ‘plastic’ phenotypes (e.g. density‐dependent dispersal) associated with metastatic cancer. These traits, which we term ‘paradoxical tumour traits’, facilitate the long‐range spread or long‐term persistence of the tumours, but offer no apparent benefit, and might even incur costs in the competition of clones within the tumour. We discuss three possible scenarios for the origin of these characters: somatic selection driven by specific selection regimes; non‐adaptive emergence due to inherent vulnerabilities in the organism; and manipulation by putative transmissible agents that contribute to and benefit from these traits. Our work highlights a lack of understanding of some aspects of tumour development, and offers alternative hypotheses that might guide further research.