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

So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Genetics and analysis of quantitative traits

Plant functional traits are the features (morphological, physiological, phenological) that represent ecological strategies and determine how plants respond to environmental factors, affect other trophic levels and influence ecosystem properties. Variation in plant functional traits, and trait syndromes, has proven useful for tackling many important ecological questions at a range of scales, giving rise to a demand for standardised ways to measure ecologically meaningful plant traits. This line of research has been among the most fruitful avenues for understanding ecological and evolutionary patterns and processes. It also has the potential both to build a predictive set of local, regional and global relationships between plants and environment and to quantify a wide range of natural and human-driven processes, including changes in biodiversity, the impacts of species invasions, alterations in biogeochemical processes and vegetation–atmosphere interactions. The importance of these topics dictates the urgent need for more and better data, and increases the value of standardised protocols for quantifying trait variation of different species, in particular for traits with power to predict plant- and ecosystem-level processes, and for traits that can be measured relatively easily. Updated and expanded from the widely used previous version, this handbook retains the focus on clearly presented, widely applicable, step-by-step recipes, with a minimum of text on theory, and not only includes updated methods for the traits previously covered, but also introduces many new protocols for further traits. This new handbook has a better balance between whole-plant traits, leaf traits, root and stem traits and regenerative traits, and puts particular emphasis on traits important for predicting species’ effects on key ecosystem properties. We hope this new handbook becomes a standard companion in local and global efforts to learn about the responses and impacts of different plant species with respect to environmental changes in the present, past and future.

/pdf/new-handbook-for-standardised-measurement-of-plant-5aljxhhg5y.pdf

New handbook for standardised measurement of plant functional traits worldwide

Species range limits involve many aspects of evolution and ecology, from species distribution and abundance to the evolution of niches. Theory suggests myriad processes by which range limits arise, including competitive exclusion, Allee effects, and gene swamping; however, most models remain empirically untested. Range limits are correlated with a number of abiotic and biotic factors, but further experimentation is needed to understand underlying mechanisms. Range edges are characterized by increased genetic isolation, genetic differentiation, and variability in individual and population performance, but evidence for decreased abundance and fitness is lacking. Evolution of range limits is understudied in natural systems; in particular, the role of gene flow in shaping range limits is unknown. Biological invasions and rapid distribution shifts caused by climate change represent large-scale experiments on the underlying dynamics of range limits. A better fusion of experimentation and theory will advance our understanding of the causes of range limits.

https://faculty.ucmerced.edu/sites/default/files/jasonsexton.com/files/sexton_2009_annualreviewofecologyevolutionandsystematics.pdf

Evolution and Ecology of Species Range Limits

Patterns of local adaptation are expected to emerge when selection is spatially heterogeneous and sufficiently strong relative to the action of other evolutionary forces. The observation of local adaptation thus provides important insight into evolutionary processes and the adaptive divergence of populations. The detection of local adaptation, however, suffers from several conceptual, statistical and methodological issues. Here, we provide practical recommendations regarding (1) the definition of local adaptation, (2) the analysis of transplant experiments and (3) the optimisation of the experimental design of local adaptation studies. Together, these recommendations provide a unified approach for measuring local adaptation and understanding the adaptive divergence of populations in a wide range of biological systems.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1111/ele.12150

A practical guide to measuring local adaptation

Two methods were evaluated for using centrifugal force to measure the occurrence of cavitation as a function of negative pressures in xylem. The general protocol was to measure the hydraulic conductivity of xylem segments (stem or root pieces) before and after centring them on a centrifuge rotor and spinning them about their long axis to generate negative xylem pressure. The percentage decrease in conductivity from the initial to final measurement was used to quantify the embolism resulting from cavitation during spinning. In one approach, segments were spun with their ends exposed to air. This method could only be used when xylem conduits were much shorter than the segment. Results from an angiosperm (Betula occidentalis) and a gymnosperm (Abies lasiocarpa) corresponded to previous observations of embolism caused by air dehydration where negative pressure was measured with the pressure chamber. Results also agreed with embolism caused by injection of air into the xylem, in support of the air-seeding hypothesis for cavitation. In a second approach, segments were spun in a rotor designed to keep the segment ends immersed in water during spinning. This gave the same results as for non-immersed segments. Immersing the segment ends allowed measurements on any material, regardless of conduit length, as demonstrated for roots of B. occidentalis. The chief advantage of the centrifugal force method is the rapidity and precision with which any desired xylem pressure can be imposed.

Use of centrifugal force in the study of xylem cavitation

Species interactions commonly coevolve as complex geo- graphic mosaics of populations shaped by differences in local selec- tion and gene flow. We use a haploid matching-alleles model for coevolution to evaluate how a pair of species coevolves when fitness interactions are reciprocal in some locations ("hot spots") but not in others ("cold spots"). Our analyses consider mutualistic and an- tagonistic interspecific interactions and a variety of gene flow patterns between hot and cold spots. We found that hot and cold spots to- gether with gene flow influence coevolutionary dynamics in four important ways. First, hot spots need not be ubiquitous to have a global influence on evolution, although rare hot spots will not have a disproportionate impact unless selection is relatively strong there. Second, asymmetries in gene flow can influence local adaptation, sometimes creating stable equilibria at which species experience min- imal fitness in hot spots and maximal fitness in cold spots, or vice versa. Third, asymmetries in gene flow are no more important than asymmetries in population regulation for determining the mainte- nance of local polymorphisms through coevolution. Fourth, intra- specific allele frequency differences among hot and cold spot pop- ulations evolve under some, but not all, conditions. That is, selection mosaics are indeed capable of producing spatially variable coevo- lutionary outcomes across the landscapes over which species interact. Altogether, our analyses indicate that coevolutionary trajectories can be strongly shaped by the geographic distribution of coevolutionary

/pdf/hot-spots-cold-spots-and-the-geographic-mosaic-theory-of-30ethmr7s4.pdf

Hot spots, cold spots, and the geographic mosaic theory of coevolution

The Red Queen hypothesis posits that sex has evolved in response to the shifting adaptive landscape generated by the evolution of interacting species. Previous studies supporting the Red Queen hypothesis have considered a narrow region of parameter space and only a subset of ecological and genetic interactions. Here, we develop a population genetics model that circumscribes a broad array of ecological and genetic interactions among species and derive the first general analytical conditions for the impact of species interactions on the evolution of sex. Our results show that species interactions typically select against sex. We conclude that, although the Red Queen favors sex under certain circumstances, it alone does not account for the ubiquity of sex.

/pdf/species-interactions-and-the-evolution-of-sex-3z7lgva7ie.pdf

Species interactions and the evolution of sex.

Coevolutionary interactions between species are thought to be an important cause of evolutionary diversification. Despite this general belief, little theoretical basis exists for distinguishing between the types of interactions that promote diversification and those types that have no effect or that even restrict it. Using analytical models and simulations of phenotypic evolution across a metapopulation, we show that coevolutionary interactions promote diversification when they impose a cost of phenotype matching, as is the case for competition or host-parasite antagonism. In contrast, classical coevolutionary arms races have no tendency to promote or inhibit diversification, and mutualistic interactions actually restrict diversification. Together with the results of recent phylogenetic and ecological studies, these results suggest that the causes of diversification in many coevolutionary systems may require reassessment.

https://www.jstor.org/stable/10.1086/657048

Scott L. Nuismer

Papers

A practical guide to measuring local adaptation

Use of centrifugal force in the study of xylem cavitation

Hot spots, cold spots, and the geographic mosaic theory of coevolution

Species interactions and the evolution of sex.

When does coevolution promote diversification