1、K1 寄生的性质要 点寄生物的多样性寄生物是摄取其他生物的组织、与其寄主紧密相联而生的捕食者的子群。寄生物可以分为两大类（ i） 微寄生物，在寄主体内或表面繁殖，（ ii） 大寄生物，在寄主体内或表面生长，但不繁殖。主要的微寄生物有病毒、细菌、真菌和原生动物。寄生蠕虫和昆虫是重要的大寄生物。一大类昆虫大寄生物是拟寄生生物，它们在昆虫寄主身上或体内产卵，通常导致寄主死亡。SARS病毒Parasites are a subgroup of predators (which consume the tissue of another living organism) that live in clo
2、se association with their host. Parasites can be classified into two broad groups: (i) microparasites, which multiply within, or on the surface of ,the host, and (ii) macroparasites which grow in or on the host, but do not multiply. The main microparasites are viruses, bacteria, fungi and protozoans
3、. Helminth worms and insects are important macroparasites. A large group of insect macroparasites are parasitoids, which lay eggs in or on the body of their insect host, and usually cause the death of the host.Key NotesThe diversity of parasitesK1 THE NATURE OF PARASITISM寄主对疾病的反应脊椎动物被微寄生物感染后产生强烈的免疫反
4、应。这种反应主要有两种成分：（ i） 细胞免疫反应，特定细胞直接攻击病原体细胞，和（ ii） B-细胞免疫反应，使抗体量上升。初次被病原体感染后，免疫记忆对未来同样的侵袭产生快速反应，导致免疫。无脊椎动物和植物也可以抑制感染，但方式较简单，通常较少特化机制。免疫造成的潜在寄主减少，使微寄生物的繁荣 -和 -破产对策加强（见 K2）传播方式 寄生物可以横向传播（在种群个体之间），或在少数情况下，纵向传播（从母体到后代）。横向传播或直接或间接，由传病媒介（如蚊子）或中间寄主做中介。艾滋病毒的传播途径细胞免疫反应Parasite transmission can be either horizont
5、al (among members of a population) or, less commonly, vertical (passed from mother to offspring). Horizontal transmission may either be direct or indirect, mediated by a vector (e.g. a mosquito) or an alternate host.Modes of transmissionIn vertebrates, infection by microparasites results in a strong
6、 immunological response. There are two components to this response: (i) the cellular immune response, where specialized cells directly attack pathogen cells, and (ii) the B-cell immune response, which gives rise to antibodies. After the first infection by a pathogen, immunological memory creates a r
7、aid response to future attacks by the same organism, resulting in immunity. Invertebrates and plants also may suppress infections, but by less sophisticated, and usually less specific mechanisms. The loss of potential hosts which immunity engenders accentuates the boom-and-bust strategy of micropara
8、sites (see Topic K2). Host response to disease复杂的生活史 许多寄生物在其生活史中不得不转换二或三种寄主。对这种复杂的生活史有三种不同的解释：（ i） 交替寄生是被寄生物感染的传病媒介（不适用于不可能成为传病媒介的不动寄主）；（ ii） 出现最适生境利用，在这种环境中，不同寄主种是不同季节或不同生活史阶段的最佳资源；（ iii） 这种模式起因于进化约束，因为寄生物在其生活史的某阶段中高度适应一种寄主，所以它们不能离开该寄主，即使在其他地方能获得更高的利益。Many parasites obligately switch between two or
9、 three host species in the course of their life cycle. Three different explanations have been advanced to explain such complex life cycles: (i) alternate hosts are vectors which have been attacked by the parasite (this cannot apply to immobile hosts which cannot be vectors); (ii)optimal habitat use
10、is occurring, where different species are the optimal resource in different seasons, or for different life cycle stage; (iii) the pattern is due to evolutionary constraint, as parasites become highly adapted to one host for part of their life cycle, they are unable to leave it even though the rewards are higher elsewhere. Complex life cycles相关主题 出生率、死亡率和种群增长（ H2） 寄生的动态（ K2） 捕食的性质（ J1）社会性寄生物 “社会性寄生物 ”与其寄主之间有一种完全不同的关系。社会性寄生物不通过摄食寄主组织获益，而是通过强迫寄主提供食物或其他利益而获利。这种关系发现在杜鹃，它们将蛋下在别种鸟的巢中，让这种鸟饲育其幼鸟。这种关系还发现在一些蚂蚁种类，它们迫使其他种工蚁给它们的幼体食品或其他利益。
