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‘Bistability’ experiments and the photoperiodic clock in the spider mite Tetranychus urticae
Author(s) -
Nunes Marlies,
Veerman Alfred
Publication year - 1997
Publication title -
entomologia experimentalis et applicata
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.765
H-Index - 83
eISSN - 1570-7458
pISSN - 0013-8703
DOI - 10.1046/j.1570-7458.1997.00215.x
Subject(s) - tetranychus urticae , spider mite , biology , population biology , population , tetranychus , library science , zoology , humanities , acari , demography , sociology , computer science , art
In insects and mites, photoperiodic induction of diapause comprises at least two processes: night-length measurement by means of a photoperiodic ‘clock’ and the subsequent accumulation of photoperiodic information contained in a sequence of light-dark cycles (photoperiodic ‘counter’). It has been shown that in many species the circadian system is involved in photoperiodic induction, but whether it plays a role in nightlength measurement itself (i.e. as the clock) or is more indirectly involved in the induction process, is still largely a matter of dispute. Many experimental protocols have been designed to try to solve this problem, and one of those is the so-called ‘bistability’ protocol. This protocol consists of so-called ‘symmetrical skeleton’ photoperiods (i.e. consisting of two short light pulses per 24 h (Pittendrigh, 1966)), with both light pulses close to 12 h apart, for example L1:D10:L1:D12. Work on circadian rhythms (e.g., the eclosion rhythm in Drosophila pseudoobscura (Pittendrigh,1966)) demonstrated that symmetrical skeleton photoperiods simulated ‘complete’ photoperiods, such that the shorter of the two dark phases was always ‘interpreted’ as light. For example, L1:D8:L1:D14 and L1:D14:L1:D8 both always simulated L10:D14. However, when the light pulses were placed close to 12 h apart, both the shorter and the longer dark phase could be interpreted as light. This region with two possible ‘interpretations’ was called the ‘zone of bistability’ (Pittendrigh, 1966). Which interpretation was adopted, depended on (1) the circadian time at which the first light pulse started and (2) the length of the first dark phase. The bistability protocol was applied to the spider mite, Tetranychus urticae. Another experimental protocol had already shown, that the mite’s clock is based on a non-circadian, or ‘hourglass’, mechanism (Veerman & Vaz Nunes, 1987). It was expected, therefore, that bistability would not occur in photoperiodic induction in this species.