Signification adaptative des différents types de développements postembryonnaires chez les Gamasides (Acariens: Anactinotriches)

Abstract

This review of the adaptive significance of various patterns of postembryonic development in the gamasid mites is restricted to the phenotypic and adaptive aspects of the different developmental patterns. Postembryonic development is redefined as beginning with achievement of embryonic ectoderm differentiation into a sclerified recognizable integument. The various kinds of postembryonic development depend on the ecology of the species and their adaptative strategies, ranging from generalized edaphic forms to more specialized species, either colonizing unpredictable habitats or being parasitic. In relation to progressive specialization, the relative duration of development tends to decrease from four active instars to three or two instars, or even to an abbreviated adult–adult cycle in endoparasitic species. One can distinguish the following main features: full development with four active instars, full development but comprising one or several phoretic instars; abbreviated development, with regressed apomorphic larva, with ovolarviparity, with regressed protonymph or with both regressed protonymph and deutonymph associated with ovolarviparity, and occasionally with phoresy. Phenotypic plasticity may occur and can be marked by facultative, behavioural, or polymorphic phoresy, facultative ovolarviparity, occasional arrhenotoky, or appearance of dormancy. The adaptive fitness of these different characters is discussed in terms of r–K selection strategies, colonizing dynamics, and specialized microhabitats. The concepts of adaptative and evolutive processes are briefly discussed, including Grandjean's theory of "l'évolution selon l'âge."