ADAPTAÇÕES DE INSETOS A MUDANÇAS NO AMBlENTE: ECOLOGIA E EVOLUÇAO DA DIAPAUSA

Abstract

Insect adaptations to environmental changes can be divided in seasonal and non-seasonal. The formers are diapause, seasonal migration, seasonal polifenism and sex ratio changes. The latter are quiescence, non-seasonal migration and non-seasonal polifenism. The overcome of these adaptations are triggered and regulated by one or by a suite of environmental cues (token stimuli) that act on different stages of the process. These cues are indicators of adverse habitat modification which can be stochastic or that may occur regularly in cycles of different lengths. Seasonal adaptations are triggered by cyclic cues and occur periodically. Non-seasonal adaptations respond to stochastic cues. Diapause and quiescence are cases of dormancy, and consist in delaying some developmental stage or in temporary metabolic supression of insect's adult life. Migrations are populational translocation between different regions. Polifenisms are adaptive morpho-physiological modifications. Finally, sex-ratio changes are genetic control of offspring's sex in order to improve parental fitness. Diapause is probably the most commonly found adaptation in insects. Empirical evidences suggest that it may act as risk-spreading strategy in natural populations and their offspring as well as a synchronization mechanism among populations and resources used by them. Although its evolutionary origins remain relatively obscure, diapause is believed to cause specialization, phylopatry and succession. Thus, it seems to have a major ecological role in population dynamics of several insect species where it is observed as well as to their associated organisms.