Fain A
Institut Royal des Sciences naturelles de Belgique, Bruxelles.
Int J Parasitol. 1994 Dec;24(8):1273-83. doi: 10.1016/0020-7519(94)90194-5.
Parasitism by mites is widespread and involves all the classes of vertebrates, from fishes to mammals. Owing to their small size and their great plasticity, mites are able to adapt to a wide range of habitats. Most of the species are ectoparasites but endoparasitism, especially in the respiratory tract, is common in birds and mammals. The morphological modifications appearing during the process adaptation to parasitic life, especially in Myobiidae, are analysed. Two kinds of characters are particularly important: the constructive specialized characters, consisting of the production of new structures, especially attachment organs allowing the mite to attach to the skin and the hair of the host, and regressive characters. Regression of the external structures is the most important phenomenon appearing in the process of evolution of parasitic mites. The importance of the regression in the parasite is correlated with the degree of evolution of the host. Host and parasite have a parallel evolution, but they go in opposite directions. The author surmises that the regressive evolution is related to the immunological reactions of the host that tend to reject the parasite. To escape from this rejection the parasite tends to select the less antigenic and therefore the most regressed phenotype. Specificity is generally strict in permanent parasites. Coevolution of host and parasite is studied in the family Myobiidae which parasitizes marsupials, insectivores, bats and rodents. The concordance between the radiations of the mites and that of their hosts is very high.
螨类寄生现象广泛存在，涉及从鱼类到哺乳动物的所有脊椎动物类别。由于螨类体型微小且具有很强的可塑性，它们能够适应广泛的栖息地。大多数螨类物种为外寄生虫，但内寄生现象，尤其是在呼吸道的内寄生现象，在鸟类和哺乳动物中很常见。本文分析了螨类在适应寄生生活过程中出现的形态变化，特别是在肌螨科中。有两类特征尤为重要：一是构造特化特征，包括产生新结构，特别是用于附着在宿主皮肤和毛发上的附着器官；二是退化特征。外部结构的退化是寄生螨类进化过程中出现的最重要现象。寄生虫退化的重要性与宿主的进化程度相关。宿主和寄生虫具有平行进化，但方向相反。作者推测，退化进化与宿主倾向于排斥寄生虫的免疫反应有关。为了逃避这种排斥，寄生虫倾向于选择抗原性较低、因此退化程度最高的表型。永久性寄生虫的特异性通常很严格。本文在寄生于有袋动物、食虫动物、蝙蝠和啮齿动物的肌螨科中研究了宿主和寄生虫的协同进化。螨类及其宿主的辐射分布之间的一致性非常高。
