Temperature-dependent structural changes in intrinsically disordered proteins: Formation of α-helices or loss of polyproline II?

Structural characterization of intrinsically disordered proteins (IDPs) is mandatory for deciphering their potential unique physical and biological properties. A large number of circular dichroism (CD) studies have demonstrated that a structural change takes place in IDPs with increasing temperature, which most likely reflects formation of transient α-helices or loss of polyproline II (PPII) content. Using three IDPs, ACTR, NHE1, and Spd1, we show that the temperature-induced structural change is common among IDPs and is accompanied by a contraction of the conformational ensemble. This phenomenon was explored at residue resolution by multidimensional NMR spectroscopy. Intrinsic chemical shift referencing allowed us to identify regions of transiently formed helices and their temperature-dependent changes in helicity. All helical regions were found to lose rather than gain helical structures with increasing temperature, and accordingly these were not responsible for the change in the CD spectra. In contrast, the nonhelical regions exhibited a general temperature-dependent structural change that was independent of long-range interactions. The temperature-dependent CD spectroscopic signature of IDPs that has been amply documented can be rationalized to represent redistribution of the statistical coil involving a general loss of PPII conformations.     

The role of ecotourism in conservation: panacea or Pandora’s box?

Does ecotourism contribute towards conservation of threatened species and habitats or is it just a marketing ploy of the tourism industry? Using 251 case studies on ecotourism from the literature, I looked at the distribution of case studies over continents, habitats and flagship species types and what factors influenced whether an ecotourism regime was perceived as ecologically sustainable by authors. Over 50% of ecotourism case studies were reported from Africa and Central America. The overall distribution of ecotourism case studies did not reflect vertebrate endemism, nor overall tourism distribution in terms of tourist numbers and receipts. There were significant differences between continents and habitats with regard to the proportion of sustainable case studies: ecotourism is perceived to be less sustainable in South America and Asia, and in island and mountain habitats. The type of flagship species also influenced whether ecotourism was classified as sustainable or not: ecotourism with no flagship species was rarely classified as sustainable while charismatic bird and mammal species were associated with a higher probability of sustainability. In a multivariate analysis, flagship species type and local community involvement were important predictors of sustainability in ecotourism. Detailed a priori planning, local involvement and control measures were perceived by authors of case studies to increase the success of ecotourism in conservation. They also perceived that ecotourism can only be an effective conservation tool under certain conditions. If these are met, the evidence indicates that ecotourism can make a contribution to conservation.     

Complement-regulatory proteins in severe malaria: too little or too much of a good thing?

Data from several laboratories suggest that erythrocyte complement-regulatory proteins, in particular complement receptor 1 (CR1), are important in the pathogenesis of severe malaria. Additional studies suggest that the levels of expression of CR1 and the complement regulator CD55 on erythrocytes vary with age, being low in young children and increasing with age. It is proposed that the interplay between the rate at which immunity develops during malaria exposure and the changes in levels of erythrocyte complement-regulatory proteins that occur with age might contribute to the differences in epidemiology of severe malaria-associated anaemia and cerebral malaria.     

Evolutionary responses of natives to introduced species: what do introductions tell us about natural communities?

Biological invasions dramatically affect the distribution, abundance and reproduction of many native species. Because of these ecological effects, exotic species can also influence the evolution of natives exposed to novel interactions with invaders. Evolutionary changes in natives in response to selection from exotics are usually overlooked, yet common responses include altered anti-predator defenses, changes in the spectrum of resources and habitats used, and other adaptations that allow native populations to persist in invaded areas. Whether a native population is capable of responding evolutionarily to selection from invaders will depend on the demographic impact of the invader, the genetic architecture and genetic variability of the native population and potentially the history of previous invasions. In some cases, natives will fail to evolve or otherwise adapt, and local or global extinction will result. In other cases, adaptive change in natives may diminish impacts of invaders and potentially promote coexistence between invaders and natives. Here, we review the evidence for evolutionary responses of native species to novel community members. We also discuss how the effects of introduced species may differ from those caused by natural range expansions of native species. Notably, introduced species may come from remote biotas with no previous evolutionary history with the native community. In addition, the rate of addition of introduced species into communities is much greater than all but the most extreme cases of historical biotic exchange. Understanding the evolutionary component of exotic/native species interactions is critical to recognizing the long-term impacts of biological invasions, and to understanding the role of evolutionary processes in the assembly and dynamics of natural communities.     

Chemically cued suppression of coral reef resilience: Where is the tipping point?

Coral reefs worldwide are shifting from high-diversity, coral-dominated communities to low-diversity systems dominated by seaweeds. This shift can impact essential recovery processes such as larval recruitment and ecosystem resilience. Recent evidence suggests that chemical cues from certain corals attract, and from certain seaweeds suppress, recruitment of juvenile fishes, with loss of coral cover and increases in seaweed cover creating negative feedbacks that prevent reef recovery and sustain seaweed dominance. Unfortunately, the level of seaweed increase and coral decline that creates this chemically cued tipping point remains unknown, depriving managers of data-based targets to prevent damaging feedbacks. We conducted flume and field assays that suggest juvenile fishes sense and respond to cues produced by low levels of seaweed cover. However, the herbivore species we tested was more tolerant of degraded reef cues than non-herbivores, possibly providing some degree of resilience if these fishes recruit, consume macroalgae, and diminish negative cues.     

Host specificity in ectomycorrhizal communities: what do the exceptions tell us?

Classic ectomycorrhizal symbioses are mutualisms that involvethe exchange of fixed carbon for mineral nutrients between plantroots and fungi. They are unique in the way they contain featuresof both intimate and diffuse symbioses. The degree of host specificityvaries, particularly among the fungi. Here we examine two exceptionalcases of specificity to see what they tell us about the advantagesof specificity, how it is initiated, and the potential rolethat it plays in complex ecosystems. The first case involvesnon-photosynthetic epiparasitic plants, which contrary to virtuallyall other plants, exhibit high levels of specificity towardtheir fungal hosts. The second case involves suilloid fungi;this is the largest monophyletic group of ectomycorrhizal fungithat is essentially restricted to associations with a singleplant family. In both cases, new symbioses are initiated bydormant propagules that are stimulated to germinate by chemicalcues from the host. This reduces the cost of wasting propaguleson non-hosts. The advantages of specificity remain unclear inboth cases, but we argue that increased benefit to the specialistmay result from specialized physiological adaptations. We reexaminethe idea that specialist fungi may help their hosts competein complex ecosystems by reducing facultative epiparasitismby other plants, and suggest an alternative hypothesis for theobserved pattern.     

Do peptide-induced changes in feeding occur because of changes in motivation to eat?

The usual paradigm in which peptides are tested for their effect on food intake involves measuring intake of readily available food. In the lever press apparatus, the subjects must "work" to get food. Such work has traditionally been used as a means of measuring motivation. Mice were trained to press a lever for milk reinforcement. After achieving a stable level of performance, we tested the effects of gastrin-related peptide (GRP), bombesin (BBS) and cholecystokinin octapeptide (CCK-8) on lever pressing. All three peptides suppressed lever pressing for milk reinforcement. Prefeeding mice with milk increased the suppression of lever pressing to a greater extent in peptide-treated mice than in saline-treated mice. As the duration of prefeeding increased, lever pressing decreased. When mice were required to make more lever presses to obtain milk, both saline- and CCK-8-treated mice increased their lever pressing. However, saline-treated mice pressed at a higher rate than CCK-8-treated mice. Unlike the results obtained with saline and CCK-8, administration of a known gustatory adversant, lithium chloride, suppressed lever pressing to the same degree in mice fed or not fed prior to training. The results are consistent with the hypothesis that these peptides act as satiety agents.     

Ion-mediated changes of xylem hydraulic resistance in planta: fact or fiction?

Although xylem provides an efficient transport pathway for water in plants, the hydraulic conductivity of xylem (K(h)) can still influence plant water status. For decades, the K(h) of functional xylem has been assumed to be constant in the short term because xylem consists of a network of dead interconnected capillary elements (conduits). Recent research has shown that K(h) can change in response to the cation content of the xylem fluid. Volume changes of pectin gel in nanometer-sized pores at inter-conduit connections are hypothesized to be the cause, and implications for xylem transport in planta are suggested. However, it seems too early to be conclusive about this phenomenon because the phenomenon has not been measured in planta with xylem fluids that realistically mimic natural xylem sap and the applied methods used to measure ion-mediated changes in K(h) have drawbacks.     

The susceptibility and resilience of corals to thermal stress: adaptation,acclimatization or both?

Coral reefs are threatened with worldwide decline from multiple factors, chief among them climate change ( Hughes et al. 2003 ; Hoegh‐Guldberg et al. 2007 ). The foundation of coral reefs is an endosymbiosis between coral hosts and their resident photosynthetic dinoflagellates (genus Symbiodinium) and this partnership (or holobiont) is exquisitely sensitive to temperature stress. The primary response to hyperthermic stress is coral bleaching, which is the loss of symbionts from coral tissues—the collapse of the symbiosis ( Weis 2008 ). Bleaching can result in increased coral mortality which can ultimately lead to severely compromised reef health ( Hoegh‐Guldberg et al. 2007 ). Despite this grim picture of coral bleaching and reef degradation, coral susceptibility to stress and bleaching is highly variable ( Coles & Brown 2003 ). There is enormous interest in discovering the factors that determine susceptibility in order to help us predict if and how corals will survive a period of rapid global warming. In this issue, Barshis et al. (2010) examine the ecophysiological and genetic basis for differential responses to stress in Porites lobata in American Samoa. They combine a reciprocal transplant experimental design between two neighbouring, but very different reef environments with state‐of‐the‐art physiological biomarkers and molecular genetic markers for both partners to tease apart the contribution of environmental and fixed influences on stress susceptibility. Their results suggest the presence of a fixed, rather than environmental effect on expression of ubiquitin conjugates, one key marker for physiological stress response. In addition, the authors show genetic differentiation in host populations between the two sites suggesting strong selection for physiological adaptation to differing environments across small geographic distances. These conclusions point the study of coral resilience and susceptibility in a new direction.     

The functional importance of parasites in animal communities: many roles at many levels?

Past research on parasites and community ecology has focussed on two distinct levels of the overall community. First, it has been shown that parasites can have a role in structuring host communities. They can have differential effects on the different hosts that they exploit, they can directly debilitate a host that itself is a key structuring force in the community, or they can indirectly alter the phenotype of their host and change the importance of the host for the community. Second, certain parasite species can be important in shaping parasite communities. Dominant parasite species can directly compete with other parasite species inside the host and reduce their abundance to some extent, and parasites that alter host phenotype can indirectly make the host more or less suitable for other parasite species. The possibility that a parasite species simultaneously affects the structure of all levels of the overall community, i.e. the parasite community and the community of free-living animals, is never considered. Given the many direct and indirect ways in which a parasite species can modulate the abundance of other species, it is conceivable that some parasite species have functionally important roles in a community, and that their removal would change the relative composition of the whole community. An example from a soft-sediment intertidal community is used to illustrate how the subtle, indirect effects of a parasite species on non-host species can be very important to the structure of the overall community. Future community studies addressing the many potential influences of parasites will no doubt identify other functionally important parasite species that serve to maintain biodiversity.     

The role of floods in the lives of fish-eating birds: predator loss or benefit?

Floods accompanied by high flow and high water turbidity are usually believed to cause problems to fish-eating birds and mammals searching visually for their prey. In the present study the diets of breeding kingfishers were studied during the normal river situation and during a long-lasting flood event with respect to diet composition, size of fish prey and food diversity index. During the normal situation (flow 1.75 m³ s^?1, Secchi disc depth 0.5–1 m), the diet of a kingfisher was dominated by benthic fish species (52.9% by numbers, 63.9% by weight), the average size of fish taken was 6.5 cm L _T and 3.0 g and the food diversity index reached its lowest value (1.57). In contrast, during the long-lasting flood event (flow 5–28 m³ s^?1, Secchi disc depth 0.03–0.4 m) the diet of the kingfisher was dominated by sub-surface fish species (72.4% by numbers, 76.1% by weight) and both the average size of fish taken (7.4 cm L _T and 3.7 g) and the food diversity index (1.83) increased significantly. The birds provided their nestlings with lower numbers of fish of larger sizes, which resulted in very similar weights of the young birds prior to fledging when the flood and normal situations were compared. This study provides evidence that in different foraging conditions the kingfishers adopt different foraging strategies to maintain their high breeding success.     

Multiple disturbances and the global degradation of coral reefs: are reef fishes at risk or resilient?

Increased frequency of disturbances and anthropogenic activities are predicted to have a devastating impact on coral reefs that will ultimately change the composition of reef associated fish communities. We reviewed and analysed studies that document the effects of disturbance‐mediated coral loss on coral reef fishes. Meta‐analysis of 17 independent studies revealed that 62% of fish species declined in abundance within 3 years of disturbances that resulted in >10% decline in coral cover. Abundances of species reliant on live coral for food and shelter consistently declined during this time frame, while abundance of some species that feed on invertebrates, algae and/or detritus increased. The response of species, particularly those expected to benefit from the immediate loss of coral, is, however, variable and is attributed to erratic replenishment of stocks, ecological versatility of species and sublethal responses, such as changes in growth, body condition and feeding rates. The diversity of fish communities was found to be negatively and linearly correlated to disturbance‐mediated coral loss. Coral loss >20% typically resulted in a decline in species richness of fish communities, although diversity may initially increase following small declines in coral cover from high coverage. Disturbances that result in an immediate loss of habitat complexity (e.g. severe tropical storms), have a greater impact on fishes from all trophic levels, compared with disturbances that kill corals, but leave the reef framework intact (e.g. coral bleaching and outbreaks of Acanthaster planci). This is most evident among small bodied species and suggests the long‐term consequences of coral loss through coral bleaching and crown‐of‐thorn starfish outbreaks may be much more substantial than the short‐term effects currently documented.     

The impact of naturalized legumes on plant communities in Northern Taiwan: are we worrying too much?

Habitat transformation caused by naturalized legumes has been considered as a profound environmental threat worldwide. However, the weight of the impact on species diversity of local native and naturalized flora has yet to be revealed. In order to gain a better understanding of the phenomenon, we developed and tested the following hypotheses: (1) naturalized legumes promote local species diversity; (2) naturalized legumes increase local naturalized species diversity rather than native biodiversity; and (3) the impact of naturalized legumes varies with habitat type. Four counties in Northern Taiwan were selected to form the study site. Nine major habitat types were identified in 100 sampling sites (1 km²/each site) in northern Taiwan, and a total of 2,242 plots (1 m²/each plot) were sampled. Species, cover, and biodiversity indices of both native and naturalized floras were obtained, and soil samples were collected from plots with and without naturalized legumes analyzed. The biodiversity and cover of the whole and naturalized flora were increased significantly by naturalized legumes, while no effects on native flora were found. The significant increase in the species diversity and cover of the whole flora and naturalized flora disappeared when naturalized legumes were excluded from the data set; the same trend was observed when habitat type was considered. Soil nitrogen was marginally significantly higher in the plots with naturalized legumes. The effects of naturalized legumes on native and naturalized floristic composition are divergent. Although species diversity and cover were increased by naturalized legumes, the additional species were naturalized legumes per se, which were the only beneficiaries of the enriched soil. The naturalized legumes did not facilitate further invasion by other exotic species, nor did they have an impact upon the native community in terms of cover, species diversity, or composition.     

Plant traits as indicators: loss or gain of information?

In this issue, Kachergis et al. provide a timely comparison of taxonomic vs functional group‐based indicators for managed steppes. The authors demonstrate how functional indicators result in only a marginal loss of taxonomic information while potentially covering community aspects not accounted for by taxa. To expand these ideas, specific plant traits could complement taxonomic indicators to achieve multiple monitoring goals.     

The fate of duplicated genes: loss or new function?

Gene duplication events are important sources of novel gene functions. However, more often than not, a duplicate gene may lose its function and become a pseudogene. What is the relative frequency of these two scenarios: functional divergence versus gene loss? Given that most non-neutral mutations are deleterious, gene loss should be far more frequent than divergence. However, a recent empirical study suggests that about 50% of all gene duplications will lead to functional divergence. The study infers the frequency of functional divergence from the size distribution of gene families produced by two successive genome duplications early in vertebrate evolution. Reasons for this unexpectedly high frequency of functional divergence are discussed.