《环境生态学-第十一章寄生的性质》由会员分享，可在线阅读，更多相关《环境生态学-第十一章寄生的性质（46页珍藏版）》请在金锄头文库上搜索。
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。 寄生（parasitism）即两种生物在一起生 活，一方受益，另一方受害，后者给前者 提供营养物质和居住场所，这种生物的关 系称为寄生。 寄生与拟寄生 ？SARS病毒甲型h1n1流感病毒寄生蜂寄生在毛毛虫体內植物中有寄生现象吗？ 寄
2、生植物 不含叶绿素或只含很少、不能自制养分的 植物，它们只以活的有机体为食，从绿色 的植物取得其所需的全部或大部分养分和 水分。而使寄主植物逐渐枯竭死亡。它们 是致命的依赖者，植物界的寄生虫。 举例菟丝子是一种生理构造特别的寄生植物 ，其组成的细胞中没有叶绿体，利用爬藤 状构造攀附在其他植物，并且从接触宿主 的部位伸出尖刺，戳入宿主直达韧皮部， 吸取养分以维生，更进一步还会储存成淀 粉粒于组织中。 肉苁蓉 是多年生肉质草本植物，其寄主很多，有梭梭、红沙、盐 爪爪和柽柳等，尤其喜欢寄生在梭梭这种耐旱木本植物的 根上。肉苁蓉真怪，一生中有三到五年是埋在沙土里生长 的。出土后生长一个月左右的时间。它
3、的茎黄色，高80 150厘米，肉质肥厚且不分枝，叶子则退化成肉质小鳞片 ，无柄，密集螺旋排列在茎上。5月间从茎顶端抽出穗状 花序。肉苁蓉露出地面的部分，几乎都由花序组成。开花 结果后，结出大量细小的种子。种子随着风沙一起飞扬， 一旦深入土层与寄主根接触，便得到寄主根分泌物的刺激 ，加上适合的温度，就开始萌发，开始新一轮的寄生生活 。桑寄生寄生于构、槐、榆、木棉、朴等树上 Parasite transmission can be either horizontal (among members of a population) or, less commonly, vertical (passe
4、d 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 transmission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。In vertebrates, infection by microparasites results in a s
5、trong 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 create
6、s a raid 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 micr
7、oparasites (see Topic K2). Host response to disease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应。这种反应主要有两种成分：（i）细胞免疫反应，特定细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） 细胞免疫反应，吞噬细胞（如白血细胞-T 淋巴细胞）攻击并吞没病原体细胞。 B-细胞免疫反应，以特定蛋白（或抗体 ）的生产
8、为基础，由B淋巴细胞结合到病原 体表面。如果再次遭遇同样病原体（或抗 原），免疫记忆会快速生产特异抗体，提 高免疫力。细胞免疫反应 行为对策（behavioral strategies）对降低寄生 水平也很重要。许多脊椎动物具备整理行为，有 效地去除外寄生物。 植物和低等动物在受到感染后也能提高免疫 力，但没有脊椎动物那样复杂的特异性。例如， 烟草植物的一片叶子被烟草花叶病毒感染后，会 提高整个植物体的防御性化学物质水平，从而增 加对多种病原体的抵抗力。食草作用也会引起类 似反应。Many parasites obligately switch between two or three hos
9、t 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 is occurri
10、ng, 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 high
11、er elsewhere. Complex life cycles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。Related topicsNatality, mortality and population The dynamics of pa
12、rasitism (K2) growth (H2) The mature of predation (J1)A completely different form of relationship is found between social parasites and their hosts. Social parasites gain benefit from their animal hosts not by feeding on their tissues but by coercing them to provide food or other benefits. Such rela
13、tionships are found in cuckoos which lay their eggs in the nests of other bird species, which then undertake the rearing of the young,and in some ant species which coerce the workers of another species to provision their brood.Social parasites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
14、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。杜鹃工蚁Vertebrate hosts commonly acquire immunity to parasites. These immune hosts are no longer available to the parasites, and the size of the susceptible population is reduced,
15、This results in a fall in the incidence of disease. However, as new susceptible hosts enter the population (for example, by birth), the disease will increase in incidence again. Thus, there is a tendency of diseases to cycle, rising as the number of new susceptibles increases and falling as the leve
16、l of immunity rises. As the influx of new susceptibles increases and falling as the level of immunity rises. As the reproductive rate of a disease falls ,the response of disease incidence to the influx of suscetibles is slower and the dynamics change from clear, synchronous cycles with a short period between peaks to reduced synchrony and longer periodicity until finally no cycles are observable.
