抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Continuing population and consumption growth will mean that the global demand for food will increase for at least another 40 years. Growing competition for land, water, and energy, in addition to the overexploitation of fisheries, will affect our ability to produce food, as will the urgent requirement to reduce the impact of the food system on the environment. The effects of climate change are a further threat. But the world can produce more food and can ensure that it is used more efficiently and equitably. A multifaceted and linked global strategy is needed to ensure sustainable and equitable food security, different components of which are explored here.

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Food Security: The Challenge of Feeding 9 Billion People

The management and conservation of the world's oceans require synthesis of spatial data on the distribution and intensity of human activities and the overlap of their impacts on marine ecosystems. We developed an ecosystem-specific, multiscale spatial model to synthesize 17 global data sets of anthropogenic drivers of ecological change for 20 marine ecosystems. Our analysis indicates that no area is unaffected by human influence and that a large fraction (41%) is strongly affected by multiple drivers. However, large areas of relatively little human impact remain, particularly near the poles. The analytical process and resulting maps provide flexible tools for regional and global efforts to allocate conservation resources; to implement ecosystem-based management; and to inform marine spatial planning, education, and basic research.

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A Global Map of Human Impact on Marine Ecosystems

The worldwide decline of coral reefs calls for an urgent reassessment of current management practices. Confronting large-scale crises requires a major scaling-up of management efforts based on an improved understanding of the ecological processes that underlie reef resilience. Managing for improved resilience, incorporating the role of human activity in shaping ecosystems, provides a basis for coping with uncertainty, future changes and ecological surprises. Here we review the ecological roles of critical functional groups (for both corals and reef fishes) that are fundamental to understanding resilience and avoiding phase shifts from coral dominance to less desirable, degraded ecosystems. We identify striking biogeographic differences in the species richness and composition of functional groups, which highlight the vulnerability of Caribbean reef ecosystems. These findings have profound implications for restoration of degraded reefs, management of fisheries, and the focus on marine protected areas and biodiversity hotspots as priorities for conservation.

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Confronting the coral reef crisis

Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

Citation classic - optimal foraging - a selective review of theory and tests

Structural complexity of the habitat often reduces predatory efficiency by reducing prey capture rates. Prey density is often positively correlated with habitat structure because it pro- vides food and substrate to the prey as well as a relative refuge from predators. Dense structure inhibits foraging, allowing abundant, highly profitable prey to coexist with predators. Sparse structure allows efficient foraging and generally contains few highly profitable prey. This suggests that feeding rates of predators may be maximized at intermediate structure. If this is true, we might also expect predator growth rates to be higher in intermediate structure habitats. Since diet breadth is thought to be related to rates of encounter with profitable prey, we also expect diets of predators to be narrower at intermediate structure than in either sparsely or densely structured habitats. Bluegill sunfish (Lepomis macrochirus) restricted to experimental ponds varying in vegetation density grew better and consumed more prey at intermediate macrophyte density than fish held at either low or high macrophyte densities. Fish at low macrophyte density had narrower diets than expected due to high initial prey availability relative to prey available at intermediate and high macro- phyte density. Fish at high macrophyte density ate fewer, but larger, prey and thus had a narrower diet than expected. Fish predation reduced total prey biomass as well as mean prey size and altered the prey community structure by removing large active invertebrate predators and herbivores with subsequent release of smaller invertebrate predators and herbivores. These changes in prey com- munity structure were also mediated by habitat structure. Habitat structure-food density interactions may be added to temperature and presence of predators as variables that influence the use of resources by fishes.

Habitat structural complexity and the interaction between bluegills and their prey

Understanding the mechanisms controlling recruitment in fishes is a major problem in fisheries science. Although the literature on recruitment mechanisms is large and growing rapidly, it is primari...

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Larval Size and Recruitment Mechanisms in Fishes: Toward a Conceptual Framework

Management of many species is currently based on an inadequate under- standing of their population dynamics. Lack of age-specific demographic information, particularly for long-lived iteroparous species, has impeded development of useful models. We use a Lefkovitch stage class matrix model, based on a preliminary life table developed by Frazer (1983a), to point to interim management measures and to identify those data most critical to refining our knowledge about the population dynamics of threatened log- gerhead sea turtles (Caretta caretta). Population projections are used to examine the sen- sitivity of Frazer's life table to variations in parameter estimates as well as the likely response of the population to various management alternatives. Current management practices appear to be focused on the least responsive life stage, eggs on nesting-beaches. Alternative protection efforts for juvenile loggerheads, such as using turtle excluder devices (TEDs), may be far more effective.

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A Stage‐Based Population Model for Loggerhead Sea Turtles and Implications for Conservation

synopsis. Ectothermic vertebrates respond to the temperature of their habitat in a manner that is remarkably similar to their response to more traditional ecological resources such as food. We review the response to temperature primarily from literature on fishes in terms of ecological concepts related to niche theory and competition. The width of the fundamental thermal niche is about 4?C when measured by a mean plus and minus one standard deviation of the distribution of temperature occupied in a laboratory gradient. Fish of temperate freshwater appear to fail into three thermal guilds along the temperature re? source axis ?cold, cool, and warm water fishes. Realized thermal niches are similar in central tendency to fundamental niches, but niche width appears to be more narrow for the realized niche in limited sample data. The success of interference competition for space with preferred temperature is tied to social dominance in a manner analogous to food competition. Thermal niche shifts in the face of interspecific competition for preferred temperature appear supported by one laboratory study. Exploitation competition in re? spect to temperature seems nebulous. If animals successfully compete for their thermal niche, growth and perhaps other measures of fitness are maximized. Cost/benefit models for thermal resources and food resources lead to similar predictions about resource use. We suggest that viewing temperature and other niche axes in the way ecologists have viewed food resources would be useful.

Temperature as an Ecological Resource

Hunting by humans played a major role in extirpating terrestrial megafauna on several continents and megafaunal loss continues today in both terrestrial and marine ecosystems. Recent declines of large marine vertebrates that are of little or no commercial value, such as sea turtles, seabirds and marine mammals, have focused attention on the ecological impacts of incidental take, or bycatch, in global fisheries. In spite of the recognition of the problem of bycatch, few comprehensive assessments of its effects have been conducted. Many vulnerable species live in pelagic habitats, making surveys logistically complex and expensive. Bycatch data are sparse and our understanding of the demography of the affected populations is often rudimentary. These factors, combined with the large spatial scales that pelagic vertebrates and fishing fleets cover, make accurate and timely bycatch assessments difficult. Here, we review the current research that addresses these challenging questions in the face of uncertainty, analytical limitations and mounting conservation crises.

Larry B. Crowder

Papers

Habitat structural complexity and the interaction between bluegills and their prey

Larval Size and Recruitment Mechanisms in Fishes: Toward a Conceptual Framework

A Stage‐Based Population Model for Loggerhead Sea Turtles and Implications for Conservation

Temperature as an Ecological Resource

Understanding impacts of fisheries bycatch on marine megafauna