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

Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

The Theory of Island Biogeography

In the early 1980s, a strategy for graphical representation of multivariate (multi-species) abundance data was introduced into marine ecology by, among others, Field, et al. (1982). A decade on, it is instructive to: (i) identify which elements of this often-quoted strategy have proved most useful in practical assessment of community change resulting from pollution impact; and (ii) ask to what extent evolution of techniques in the intervening years has added self-consistency and comprehensiveness to the approach. The pivotal concept has proved to be that of a biologically-relevant definition of similarity of two samples, and its utilization mainly in simple rank form, for example ‘sample A is more similar to sample B than it is to sample C’. Statistical assumptions about the data are thus minimized and the resulting non-parametric techniques will be of very general applicability. From such a starting point, a unified framework needs to encompass: (i) the display of community patterns through clustering and ordination of samples; (ii) identification of species principally responsible for determining sample groupings; (iii) statistical tests for differences in space and time (multivariate analogues of analysis of variance, based on rank similarities); and (iv) the linking of community differences to patterns in the physical and chemical environment (the latter also dictated by rank similarities between samples). Techniques are described that bring such a framework into place, and areas in which problems remain are identified. Accumulated practical experience with these methods is discussed, in particular applications to marine benthos, and it is concluded that they have much to offer practitioners of environmental impact studies on communities.

Non-parametric multivariate analyses of changes in community structure

Human alteration of Earth is substantial and growing. Between one-third and one-half of the land surface has been transformed by human action; the carbon dioxide concentration in the atmosphere has increased by nearly 30 percent since the beginning of the Industrial Revolution; more atmospheric nitrogen is fixed by humanity than by all natural terrestrial sources combined; more than half of all accessible surface fresh water is put to use by humanity; and about one-quarter of the bird species on Earth have been driven to extinction. By these and other standards, it is clear that we live on a human-dominated planet.

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Human Domination of Earth's Ecosystems

Pseudoreplication is defined. as the use of inferential statistics to test for treatment effects with data from experiments where either treatments are not replicated (though samples may be) or replicates are not statistically independent. In ANOVA terminology, it is the testing for treatment effects with an error term inappropriate to the hypothesis being considered. Scrutiny of 176 experi- mental studies published between 1960 and the present revealed that pseudoreplication occurred in 27% of them, or 48% of all such studies that applied inferential statistics. The incidence of pseudo- replication is especially high in studies of marine benthos and small mammals. The critical features of controlled experimentation are reviewed. Nondemonic intrusion is defined as the impingement of chance events on an experiment in progress. As a safeguard against both it and preexisting gradients, interspersion of treatments is argued to be an obligatory feature of good design. Especially in small experiments, adequate interspersion can sometimes be assured only by dispensing with strict random- ization procedures. Comprehension of this conflict between interspersion and randomization is aided by distinguishing pre-layout (or conventional) and layout-specifit alpha (probability of type I error). Suggestions are offered to statisticians and editors of ecological j oumals as to how ecologists' under- standing of experimental design and statistics might be improved.

/pdf/pseudoreplication-and-the-design-of-ecological-field-44o8kzdaoi.pdf

Pseudoreplication and the Design of Ecological Field Experiments

Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis.

On a shallow sand flat at Princess Royal Harbour near Albany, Western Australia, the brown macrophyte Hormosira banksii attaches to shells of infaunal bivalves. Hormosira occupies shells of Katelysia rhytiphora in preference to K. scalarina. We proposed and tested four hypotheses to explain this host occupation pattern. First, by following the fate of nearly one thousand marked clams of each species, we rejected the hypothesis that K. rhytiphora exhibits greater longevity and simply possesses more frequent Hormosira because of a longer temporal integration of settlement events. Second, we rejected the hypothesis that K. rhytiphora exhibits higher densities in the top 5 mm of sediment and accumulates more Hormosira because its shell is more abundant in the depth range occupied by the attaching base of Hormosira. Third, we showed that K. rhytiphora because of its larger size is more difficult to dislodge from the sediments than K. scalarina, supporting the hypothesis that Hormosira is rare on K. scalarina because storm waves selectively dislodge and carry to the beach Hormosira attached to K. scalarina. This physical explanation for the Hormosira occupation pattern gets further support from the observation that a third infaunal bivalve, the mussel Brachidontes erosus, has a far higher frequency of Hormosira occupation than either Katelysia species, while providing a much more robust anchor because of its extensive byssal attachments to neighboring mussels. The sizes of Hormosira plants also vary consistently with this physical transport hypothesis: Hormosira is smallest on K. scalarina and largest on B. erosus. Successful colonization of initially unoccupied Katelysia during five 3–9 month periods was also more frequent on K. rhytiphora than on K. scalarina. This suggests a fourth explanation for the Hormosira distribution pattern: that spore settlement is selective for K. rhytiphora in preference to K. scalarina. Although this hypothesis requires further testing, evolution of selective spore settlement would be reasonable given the different likelihoods of subsequent host dislodgement during storm waves.

Biological vs. physical explanations for the non-random pattern of host occupation by a macroalga attaching to infaunal bivalve molluscs

Despite increasing use of dredged mate- rials as beach fill to protect coastal property and public beaches from storm damage, knowledge of how this practice affects sandy beach ecosystems re- mains poor. We coupled field monitoring of 2 succes- sive beach disposal events with mesocosm experi- ments to assess mechanisms of ecological effects of fine sediment disposal. Macrobenthic sampling on Topsail Island, North Carolina, revealed that disposal of dredge spoils transformed beach grain sizes from medium to fine sand. Water sampling documented substantially elevated surf-zone turbidity during and occasionally after sediment deposition. When disposal occurred before spring invertebrate recruitment to the beach, it negatively influenced recruitment of the mole crab Emerita talpoida and the amphipod Para- haustorius longimerus. When disposal followed re- cruitment, it affected abundances of the bean clam Donax variabilis and 3 species of haustoriid am- phipods negatively, and abundance of the spionid polychaete Scolelepis squamata positively. Effects lasted for the full warm season, and suppressions of invertebrate abundances were repeated across suc- cessive annual disposal events. In mesocosms, turbid- ity matching that induced in the field slowed growth of clams and modified habitat choices by predatory fishes. Hence, annual disposal of fine-grained dredge spoils on these sandy beaches maintained depressed abundances of 5 of 6 macroinvertebrate prey of shore- bird and surf fish, without sustaining elevated volumes of beach sediments as long as a year. Implementation of disposal projects before the beginning of the sea- sonal recruitment of benthos resulted in fewer nega- tive impacts on abundance than disposal projects con- ducted after the recruitment season, probably reflecting a more universal risk from burial and suffocation.

/pdf/dominant-macrobenthic-populations-experience-sustained-4bzygx2oyh.pdf

Charles H. Peterson

Papers

Interacting effects of temperature and salinity on Bonamia sp. parasitism in the Asian oyster Crassostrea ariakensis.

Biological vs. physical explanations for the non-random pattern of host occupation by a macroalga attaching to infaunal bivalve molluscs

Dominant macrobenthic populations experience sustained impacts from annual disposal of fine sediments on sandy beaches

Drilling by buccinid gastropods of the genus Cominella in Australia

Spatio-temporal patterns in the mortality of bay scallop recruits in North Carolina: Investigation of a life history anomaly