植物警戒色的研究进展

植物为适应植食动物的取食压力而进化出物理、化学等多种防御机制,以把植食伤害降到最低程度,但动物不断的抽样尝试行为还是让有防御行为的植物受到伤害。因此,向潜在的植食动物传达自己的防御信号对植物是有益的。颜色作为一种稳定有效的视觉信号通常是花和果实的诱惑信号,某些情况下也是一种警戒防御信号,植食动物经过抽样学习后能识别这种防御信号并主动回避,从而形成了植物的警戒色。起源于猎物-捕食者关系的警戒色理论在动物界得到了充分研究,但植物警戒色却不为人所知,直到2001年Hamilton关于秋季树叶颜色的信号假说公开发表后,才引起人们对植物警戒色的初步研究。如今在早秋变色树种、幼叶、多剌植物、植物繁殖器官都发现了警戒色的一些例证,尽管有些还不太明确甚至存在争议,但至少为植物警戒色的进一步研究奠定了基础。植物营养体颜色在时空上的多态性变化值得人们更深入地研究,防御权衡假说也预示了防御有害植食动物的警戒作用存在于繁殖器官的可能性,研究它们生理和生态适应意义有利于人们更深程度地理解植物-动物之间的复杂关系。     

The effects of livestock grazing on biodiversity are multi‐trophic: a meta‐analysis

Anthropogenic disturbance has generated a significant loss of biodiversity worldwide and grazing by domestic herbivores is a contributing disturbance. Although the effects of grazing on plants are commonly explored, here we address the potential multi‐trophic effects on animal biodiversity (e.g. herbivores, pollinators and predators). We conducted a meta‐analysis on 109 independent studies that tested the response of animals or plants to livestock grazing relative to livestock excluded. Across all animals, livestock exclusion increased abundance and diversity, but these effects were greatest for trophic levels directly dependent on plants, such as herbivores and pollinators. Detritivores were the only trophic level whose abundance decreased with livestock exclusion. We also found that the number of years since livestock was excluded influenced the community and that the effects of grazer exclusion on animal diversity were strongest in temperate climates. These findings synthesise the effects of livestock grazing beyond plants and demonstrate the indirect impacts of livestock grazing on multiple trophic levels in the animal community. We identified the potentially long‐term impacts that livestock grazing can have on lower trophic levels and consequences for biological conservation. We also highlight the potentially inevitable cost to global biodiversity from livestock grazing that must be balanced against socio‐economic benefits.     

Exploitation of secondary metabolites by animals: A response to homeostatic challenges

We propose that the exploitation of the bioactive properties of secondary metabolites (SMs) by animals can provide a "treatment" against various challenges that perturb homeostasis in animals. The unified theoretical framework for the exploitation of SMs by animals is based on a synthesis of research from a wide range of fields and although it is focused on providing generalized predictions for herbivores that exploit SMs of plants, predictions can be applied to understand the exploitation of SMs by many animals. In this review, we argue that the probability of SM exploitation is determined by the relative difference between the cost of a homeostatic challenge and the toxicity of the SM and we provide various predictions that can be made when considering behavior under a homeostatic perspective. The notion that animals experience and respond to costly challenges by exploiting therapeutic SMs provides a relatively novel perspective to explain foraging behavior in herbivores, specifically, and behavior of animals in general. We provide evidence that animals can exploit the biological activity of SMs to mitigate the costs of infection by parasites, enhance reproduction, moderate thermoregulation, avoid predation, and increase alertness. We stress that a better understanding of animal behavior requires that ecologists look beyond their biases that SMs elicit punishment and consider a broader view of avoidance or selection of SMs relative to the homeostatic state. Finally, we explain how understanding exploitation of SMs by animals could be applied to advance practices of animal management and lead to discovery of new drugs.     

Impacts of invasive plants on resident animals across ecosystems,taxa, and feeding types: a global assessment

As drivers of global change, biological invasions have fundamental ecological consequences. However, it remains unclear how invasive plant effects on resident animals vary across ecosystems, animal classes, and functional groups. We performed a comprehensive meta‐analysis covering 198 field and laboratory studies reporting a total of 3624 observations of invasive plant effects on animals. Invasive plants had reducing (56%) or neutral (44%) effects on animal abundance, diversity, fitness, and ecosystem function across different ecosystems, animal classes, and feeding types while we could not find any increasing effect. Most importantly, we found that invasive plants reduced overall animal abundance, diversity and fitness. However, this significant overall effect was contingent on ecosystems, taxa, and feeding types of animals. Decreasing effects of invasive plants were most evident in riparian ecosystems, possibly because frequent disturbance facilitates more intense plant invasions compared to other ecosystem types. In accordance with their immediate reliance on plants for food, invasive plant effects were strongest on herbivores. Regarding taxonomic groups, birds and insects were most strongly affected. In insects, this may be explained by their high frequency of herbivory, while birds demonstrate that invasive plant effects can also cascade up to secondary consumers. Since data on impacts of invasive plants are rather limited for many animal groups in most ecosystems, we argue for overcoming gaps in knowledge and for a more differentiated discussion on effects of invasive plant on native fauna.     

Ultraviolet radiation,resistance to infectious diseases,and vaccination responses

Exposure to ultraviolet (UV) radiation, as in sunlight, can modulate immune responses in animals and humans. This immunomodulation can lead to positive health effects especially with respect to certain autoimmune diseases and allergies. However, UV-induced immunomodulation has also been shown to be deleterious. Experimental animal studies have revealed that UV exposure can impair resistance to many infectious agents, such as bacteria, parasites, viruses, and fungi. Importantly, these effects are not restricted to skin-associated infections, but also concern systemic infections. The real consequences of UV-induced immunomodulation on resistance to infectious diseases are not known for humans. Risk estimations have been performed through extrapolation of animal data, obtained from infection models, to the human situation. This estimation indicated that UV doses relevant to outdoor exposure can impair the human immune system sufficiently to have effects on resistance to infections. To further quantify and validate this risk estimation, data, e.g., from human volunteer studies, are necessary. Infection models in humans are not allowed for ethical reasons. However, vaccination against an infectious disease evokes a similar immune response as the pathogen and thereby provides an opportunity to measure the effect of UV radiation on the immune system and an estimate of the possible consequences of altered resistance to infectious agents. Effects of controlled UVB exposure on immune responses after hepatitis B vaccination have been established in mice and human volunteers. In mice, cellular and Th1-associated humoral immune responses to hepatitis B were significantly impaired, whereas in human volunteers no significant effect of UVB on these responses could be found. Preliminary data indicate that cytokine polymorphisms might be, at least in part, responsible for interindividual differences in immune responses and in susceptibility to UVB-induced immunomodulation. In addition, adaptation to UV exposure needs to be considered as a possible explanation for the difference between mice and humans that was observed in the hepatitis B vaccination model.     

Plant behaviour and communication

Plant behaviours are defined as rapid morphological or physiological responses to events, relative to the lifetime of an individual. Since Darwin, biologists have been aware that plants behave but it has been an underappreciated phenomenon. The best studied plant behaviours involve foraging for light, nutrients, and water by placing organs where they can most efficiently harvest these resources. Plants also adjust many reproductive and defensive traits in response to environmental heterogeneity in space and time. Many plant behaviours rely on iterative active meristems that allow plants to rapidly transform into many different forms. Because of this modular construction, many plant responses are localized although the degree of integration within whole plants is not well understood. Plant behaviours have been characterized as simpler than those of animals. Recent findings challenge this notion by revealing high levels of sophistication previously thought to be within the sole domain of animal behaviour. Plants anticipate future conditions by accurately perceiving and responding to reliable environmental cues. Plants exhibit memory, altering their behaviours depending upon their previous experiences or the experiences of their parents. Plants communicate with other plants, herbivores and mutualists. They emit cues that cause predictable reactions in other organisms and respond to such cues themselves. Plants exhibit many of the same behaviours as animals even though they lack central nervous systems. Both plants and animals have faced spatially and temporally heterogeneous environments and both have evolved plastic response systems.     

Exploiting scents of distress: the prospect of manipulating herbivore-induced plant odours to enhance the control of agricultural pests

In response to feeding by arthropods, plants actively and systemically emit various volatile substances. It has been proposed that these herbivore-induced volatiles (HIPVs) can be exploited in agricultural pest control because they might repel herbivores and because they serve as attractants for the enemies of the herbivores. Indeed, recent studies with transgenic plants confirm that odour emissions can be manipulated in order to enhance the plants' attractiveness to beneficial arthropods. An additional advantage of manipulating HIPV emissions could be their effects on neighbouring plants, as a rapidly increasing number of studies show that exposure to HIPVs primes plants for augmented defence expression. Targeting the right volatiles for enhanced emission should lead to ecologically and economically sound ways of combating important pests.     

植物次生代谢物对植食性哺乳动物营养和生理生态特征的影响

植物次生代谢物对植食性哺乳动物的营养和生理生态效应是动植物相互关系研究中的一个重要方面。本文简要介绍了植食性哺乳动物处理植物次生代谢物的一般途径,着重阐述了植物次生代谢物对植食性哺乳动物的营养和生理特征的限制方式,并对决定植食性哺乳动物处理植物次生代谢物能力差异性的相关因素进行了探讨。最后,结合国际上的研究趋势,论述了国内开展此类研究的方向和重点。     

Genistein

Genistein (4',5,7-trihydroxyisoflavone) is a common precursor in the biosynthesis of antimicrobial phytoalexins and phytoanticipins in legumes, and an important nutraceutical molecule found in soybean seeds. Genistein is a phytoestrogen with a wide variety of pharmacological effects in animal cells, including tyrosine kinase inhibition, and dietary genistein ingestion has been linked, through epidemiological and animal model studies, with a range of potential health beneficial effects. These include chemoprevention of breast and prostate cancers, cardiovascular disease and post-menopausal ailments. In spite of an extensive literature on the effects of dietary genistein, questions still exist as to its potential overall benefits as a component of the human diet. Genistein can be synthesized chemically via the deoxybenzoin or chalcone route. Genistein is synthesized in plants from the flavanone naringenin by a novel ring migration reaction catalyzed by the cytochrome P450 enzyme isoflavone synthase (IFS). IFS genes have recently been cloned from a number of plant species, and production of genistein can be now achieved in non-legumes by recombinant DNA approaches.     

UV and pigmentation: molecular mechanisms and social controversies

Ultraviolet radiation (UVR) is an essential risk factor for the development of premalignant skin lesions as well as of melanoma and non-melanoma skin cancer. UVR exerts many effects on the skin, including tanning, carcinogenesis, immunomodulation, and production of vitamin D. Vitamin D (vit D) is important in the maintenance of healthy bones as well as other purported beneficial effects, amongst which is the potential for reducing risk of malignancy--though oral supplementation is fully capable of maintaining systemic levels. The known medical harm from UV exposure relates primarily to cancer of the skin--the most common organ in man to be affected by cancer. In this review, we summarize the knowledge about the ultraviolet (UV) response in regards to inflammation, immunosuppression, carcinogenesis and the tanning response. We also discuss vit D and UV, as well as public health implications of tanning behavior and commercial interests related to the promotion of UV exposure. As the most ubiquitous human carcinogen, UVR exposure represents both a challenge and enormous opportunity in the realm of skin cancer prevention.     

Biogeochemistry of selenium and its impact on food chain quality and human health

In areas where soils are low in bioavailable selenium (Se), potential Se deficiencies cause health risks for humans. Though higher plants have been considered not to require this element, the experience with low-Se soils in Finland has provided evidence that the supplementation of commercial fertilizers with sodium selenate affects positively not only the nutritive value of the whole food chain from soil to plants, animals and humans but also the quantity of plant yields. The level of Se addition has been optimal, and no abnormally high concentrations in plants or in foods of animal origin have been observed. Se levels in serum and human milk indicate that the average daily intake has been within limits considered to be safe and adequate. In fact, plants act as effective buffers, because their growth is reduced at high Se levels. They also tend to synthesize volatile compounds in order to reduce excess Se. On the other hand, when added at low concentrations, Se exerts a beneficial effect on plant growth via several mechanisms. As in humans and animals, Se strengthens the capacity of plants to counteract oxidative stress caused by oxygen radicals produced by internal metabolic or external factors. At proper levels it also delays some of the effects of senescence and may improve the utilization of short-wavelength light by plants. High additions are toxic and may trigger pro-oxidative reactions. Thus, the present supplementation of fertilizers with Se can be considered a very effective and readily controlled way to increase the average daily Se intake nationwide.     

Mandatory " enriched" housing of laboratory animals: the need for evidence-based evaluation

Environmental enrichment for laboratory animals has come to be viewed as a potential method for improving animal well-being in addition to its original sense as a paradigm for learning how experience molds the brain. It is suggested that the term housing supplementation better describes the wide range of alterations to laboratory animal housing that has been proposed or investigated. Changes in the environments of animals have important effects on brain structure, physiology, and behavior--including recovery from illness and injury--and on which genes are expressed in various organs. Studies are reviewed that show how the brain and other organs respond to environmental change. These data warrant caution that minor cage supplementation intended for improvement of animal well-being may alter important aspects of an animal's physiology and development in a manner not easily predicted from available research. Thus, various forms of housing supplementation, although utilized or even preferred by the animals, may not enhance laboratory animal well-being and may be detrimental to the research for which the laboratory animals are used.     

Extending the stress‐gradient hypothesis – is competition among animals less common in harsh environments?

The role of positive interactions has become widely accepted as a mechanism shaping community dynamics. Most empirical evidence comes from plant communities and sessile marine organisms. However, evidence for the relative role of positive interactions in organizing terrestrial animal communities is more limited, and a general framework that includes positive interactions among animals is lacking. The ‘stress gradient hypothesis’ (SGH) developed by plant ecologists predicts that the balance between positive and negative interactions will vary along gradients of biotic and abiotic stress, with positive interactions being more important in stressful environments. Paralleling the SGH, stress gradients for terrestrial herbivores could be equated to inverse primary productivity gradients, so we would expect positive interactions to prevail in more stressful, low productivity environments. However, this contradicts the typical view of terrestrial animal ecology that low primary productivity systems will foster intense competition for resources among consumers. Here we use alpine herbivores as a case study to test one of the predictions of the SGH in animal communities, namely the prevalence of positive interactions in low productivity environments. We identify potential mechanisms of facilitation and review the limited number of examples of interspecific interactions among alpine herbivores to assess the role of positive and negative interactions in structuring their communities. A meta‐analysis showed no clear trend in the strength and direction of interactions among alpine herbivores. Although studies were biased towards reporting significant negative inter actions, we found no evidence of competition dominating in harsh environments. Thus, our results only partially support the SGH, but directly challenge the dominant view among animal ecologists. Clearly, a sound theoretical framework is needed to include competition, positive and neutral interactions as potential mechanisms determining the structure of animal communities under differing environmental conditions, and the stress‐gradient hypothesis can provide a solid starting point.     

Sekundärstoffe – die Geheimwaffen der Pflanzen

Secondary metabolites Already 400 million years ago when land plants evolved, they probably produced secondary metabolites as means of defence against herbivores, microbes and competing plants. Secondary metabolites usually are bioactive agents, which can interfere with molecular targets in animals and microbes. Therefore, many plants and substances isolated from them can serve as valuable drugs in medicine and pharmacy. Some secondary metabolites also serve as signal compounds to attract pollinating animals and seed‐dispersing animals, but also for UV protection, as antioxidants or mobile nitrogen stores. Biology and evolution but also physiological and genetic bases of secondary metabolism are discussed in this overview.     

Biogeochemistry of selenium and its impact on food chain quality and human health

In areas where soils are low in bioavailable selenium (Se), potential Se deficiencies cause health risks for humans. Though higher plants have been considered not to require this element, the experience with low-Se soils in Finland has provided evidence that the supplementation of commercial fertilizers with sodium selenate affects positively not only the nutritive value of the whole food chain from soil to plants, animals and humans but also the quantity of plant yields. The level of Se addition has been optimal, and no abnormally high concentrations in plants or in foods of animal origin have been observed. Se levels in serum and human milk indicate that the average daily intake has been within limits considered to be safe and adequate. In fact, plants act as effective buffers, because their growth is reduced at high Se levels. They also tend to synthesize volatile compounds in order to reduce excess Se. On the other hand, when added at low concentrations, Se exerts a beneficial effect on plant growth via several mechanisms. As in humans and animals, Se strengthens the capacity of plants to counteract oxidative stress caused by oxygen radicals produced by internal metabolic or external factors. At proper levels it also delays some of the effects of senescence and may improve the utilization of short-wavelength light by plants. High additions are toxic and may trigger pro-oxidative reactions. Thus, the present supplementation of fertilizers with Se can be considered a very effective and readily controlled way to increase the average daily Se intake nationwide.     

Unpaved roads disrupt the effect of herbivores and pollinators on the reproduction of a dominant shrub

Anthropogenic linear developments, such as trails and firebreaks, also called soft linear developments (SLD), can influence animal behavior, altering the ecological interactions in which animals are involved. For example, SLD can affect the behavior of pollinators and herbivores, but little is known about the combined effect of these three elements on plant reproduction.We evaluated the combined effect of SLD, insect pollinators and herbivores (ungulates) on three reproductive output variables (fruit set, seed set, and seed mass) of a Mediterranean shrub (Halimium halimifolium). We considered two different habitats (SLD verges vs. adjacent scrublands), two scenarios of herbivory (with and without ungulates), and three scenarios of pollinator activity (without pollinators, with manual pollination and with natural pollination).SLD had contrasting effects on H. halimifolium reproduction. In the absence of herbivores, overall fruit set was lower in the verges of SLD than in adjacent scrublands, probably due to lower flower pollination rates. Where herbivores were present, overall fruit set was similar between habitats, because ungulate browsing was lower in SLD verges than in adjacent scrublands. The quantity and weight of seeds per fruit was similar in both habitats, probably because all fertilized flowers received similar amounts of pollen.SLD can alter the interaction among pollinators, herbivores and plants, leading to changes in the reproductive performance of the latter. These changes can have strong negative impacts on endangered plants that rely on fruit and seed production to persist. However, SLD verges could be safe places for plants particularly sensitive to herbivory by ungulates.     

When are ant-attractant devices a worthwhile investment? Vicia faba extrafloral nectaries and Lasius niger ants

Most studies aiming to determine the beneficial effect of ants on plants simply consider the effects of the presence or exclusion of ants on plant yield. This approach is often inadequate, however, as ants interact with both non-tended herbivores and tended Homoptera. Moreover, the interaction with these groups of organisms is dependent on ant density, and these functional relationships are likely to be non-linear. A model is presented here that segregates plant herbivores into two categories depending on the sign of their numerical response to ants (myrmecophiles increase with ants, non-tended herbivores decline). The changes in these two components of herbivores with increasing ant density and the resulting implications for ant-plant mutualisms are considered. It emerges that a wide range of ant densities needs to be considered as the interaction sign (mutualism or parasitism) and strength is likely to change with ant density. The model is used to interpret the results of an experimental study that varied levels of Aphis fabae infestation and Lasius niger ant attendance on Vicia faba bean plants. Increasing ant density consistently reduced plant fitness and thus, in this location, the interaction between the ants and the plant can be considered parasitic. In the Vicia faba system, these costs of ants are unlikely to be offset by other beneficial agents (e.g., parasitoids), which also visit extrafloral nectaries.     

Screening of yeasts as probiotic based on capacities to colonize the gastrointestinal tract and to protect against enteropathogen challenge in mice

Probiotics are defined as viable microorganisms that exhibit a beneficial effect on the host's health when they are ingested. Two important criteria are used for selection of probiotic microorganisms: they must be able to survive in the gastrointestinal environment and to present at least one beneficial function (colonization resistance, immunomodulation or nutritional contribution). Generally, in vitro assays demonstrating these properties were used to select probiotics but it is unclear if the data can be extrapolated to in vivo conditions. In the present work, twelve Saccharomyces cerevisiae strains isolated from different environments (insect association, tropical fruit, cheese and "aguardente" production) and pre-selected for in vitro resistance to simulated gastrointestinal conditions were inoculated in germ-free mice to evaluate their real capacity to colonize the mammal digestive tract. Using these data, one of the yeasts (S. cerevisiae 905) was selected and tested in gnotobiotic (GN) and conventional (CV) mice for its capacity to protect against oral challenge with two enteropathogenic bacteria (Salmonella Typhimurium and Clostridium difficile). The yeast reached populational levels potentially functional in the gastrointestinal portions where the enteropathogens tested act. No antagonism against either pathogenic bacterium by the yeast was observed in the digestive tract of GN mice but, after challenge with S. Typhimurium, mortality was lower and liver tissue was better preserved in CV animals treated with the yeast when compared with a control group (p<0.05). Histopathological results of intestines showed that the yeast also presented a good protective effect against oral challenge with C. difficile in GN mice (p<0.05). In conclusion, among the 12 S. cerevisiae tested, strain 905 showed the best characteristics to be used as a probiotic as demonstrated by survival capacity in the gastrointestinal tract and protective effect of animals during experimental infections.     

Population,community and ecosystem effects of exotic herbivores: A growing global concern

Exotic herbivores represent a serious threat to native biodiversity, producing large scale changes in native communities and altering ecosystem processes. In this special issue, we present a series of case studies and reviews from different areas of the world that highlight (1) the consequences of herbivore introductions are a global problem; (2) they can result in wholesale shifts in the distribution of dominant plants on the landscape and; (3) the effects of herbivore introductions extend from the population to the community and ecosystem level. These studies suggest that introduced herbivores often retard ecosystem recovery after disturbance, facilitate invasion of plant species and can act as selective agents on native plant communities. These studies also suggest that several topics, including facilitation between exotic herbivores and exotic plants and animals (i.e., invasional meltdown) and the effect of exotic herbivores on ecosystem processes, require more research attention. Overall the papers in this special feature suggest that introduced herbivores are a global problem with wide-ranging ecological and evolutionary effects.     

Faecal corticosteroid levels as an indicator of well-being in the tammar wallaby, Macropus eugenii

Faecal corticosteroid levels were measured in five female tammar wallabies, Macropus eugenii, at Macquarie University, NSW, Australia, to assess their reliability as indicators of well-being in this species. Animals were challenged with a change in conditions over the course of approximately 1 week, comprising movement from group yards to isolation in individual yards, in order to impose a disturbance to homeostasis ("stress"). Faecal samples were collected in 24-h intervals during the study period and analysed for corticosteroid concentration. The use of enzyme immunoassay for the measurement of corticosteroids in marsupial faecal pellets was validated. We observed a significant increase in faecal corticosteroids upon isolation and movement. Faecal corticosteroids remained above initial levels in all five animals throughout the study period, suggesting that faecal corticosteroid concentrations may be a useful indicator of a change in animal well-being. Faecal corticosteroid levels did not correlate with serum cortisol levels, implying that the use of noninvasive methods in a representative marsupial, the tammar wallaby, has the potential to provide information that is not readily apparent using blood-based protocols. Faecal corticosteroid analysis therefore has the potential for application in monitoring the well-being of captive and managed marsupial populations, as part of an integrated system of measures of animal health and well-being.