Diapause and quiescence as two main kinds of dormancy and their significance in life cycles of mites and ticks (Chelicerata: Arachnida: Acari). part 1. Acariformes

Abstract

A review of available data on diapause and quiescence as two main kinds of dormancy in life histories of the acari- form mites (Arachnida: Acari), particularly of Oribatida, Astigmata and Prostigmata, and on the role of both dormant states in life cycles of these mites due to their adaptations to predictable (seasonal) and unpredictable (irregular) environmental changes. The survival during periods of adverse conditions is enabled in the acariform mites by both kinds of dormancy controlled either endog-enously (diapause), or exogenously (quiescence), and also in both ways. However, the role of dormancy in the control of life-cycle seasonality, well known for diapause, is doubtful for the common form of quiescence, arisen as a direct response to unfavorable environmental changes at any life-cycle stage, and called as “the stage-independent quiescence”. However another form, ascer-tained in insects as “the post-diapause quiescence”, and characteristic of many acariform mites also, is of great significance for seasonal time-adjustment in both these groups of terrestrial arthropods. Similar function is characteristic probably of “the stage-specific quiescence” ascertained theoretically for insects. Representatives of the Acari reveal a high diversity of the life-cycle seasonal control systems (from plesiotypic types with numerous diapause-capable ontogenetic stages up to apotypic types with single or limited number of such stages, also enabling the reliable life-cycle seasonality). An adaptation to environmental unpredict-ability in mites with plesiotypic systems is based on overlapping flexible life cycles (with capability of some stages for quiescence also), while in mites with apotypic systems – on special resting stage (often with phoretic dispersal). A combination of diapause and post-diapause quiescence known in many extant prostigmatid mites is suggested as an initial ancestral state of dormancy in adaptations of acariform mites (particularly of Oribatida) to adverse environmental changes. Such a hypothesis gives reason-able solution of controversial interpretations concerning the nature of dormancy in extant oribatid mites during their hibernation.