Insect circadian rhythms and photoperiodism

Abstract

Two clock-controlled processes, overt circadian rhythmicity and the photoperiodic induction of diapause, are described in the blow fly, Calliphora vicina and the fruit fly, Drosophila melanogaster. Circadian locomotor rhythms of the adult flies reflect endogenous, self-sustained oscillations with a temperature compensated period. The free-running rhythms become synchronised (entrained) to daily light:dark cycles, but become arrhythmic in constant light above a certain intensity. Some flies show fragmented rhythms (internal desynchronisation) suggesting that overt rhythmicity is the product of a multioscillator (multicellular) system. Photoperiodic induction of larval diapause in C. vicina and of ovarian diapause in D. melanogaster is also based on the circadian system but seems to involve a separate mechanism at both the molecular and neuronal levels. For both processes in both species, the compound eyes and ocelli are neither essential nor necessary for photic entrainment, and the circadian clock mechanism is not within the optic lobes. The central brain is the most likely site for both rhythm generation and extra-optic photoreception. In D. melanogaster, a group of lateral brain neurons has been identified as important circadian pacemaker cells, which are possibly also photo-sensitive. Similar lateral brain neurons, staining for arrestin, a protein in the phototransduction 'cascade' and a selective marker for photoreceptors in both vertebrates and invertebrates, have been identified in C. vicina. Much less is known about the cellular substrate of the photoperiodic mechanism, but this may involve the pars intercerebralis region of the mid-brain.

A Functional Link between Rhythmic Changes in Chromatin Structure and theArabidopsisBiological Clock

“…The use of daylength cues allows organisms to track time of year and to anticipate predictable annual variations in environmental signals. An accurate photoperiodic perception is essential in maintaining appropriate clock-dependent phase relationships with the external day/night cycles (Saunders, 1997;Oster et al, 2002;Johnson et al, 2003;Merrow et al, 2006). Plants also use the circadian clock to perceive the changing photoperiods and to synchronize gene expression and physiology to the most favorable seasons (Má s, 2005;McClung, 2006).…”

Period gene expression in relation to seasonality and circadian rhythms in the linden bug, Pyrrhocoris apterus (Heteroptera)

“…The relationship between these two phenomena is still largely unresolved. Formal properties of photoperi odic responses indicate that photoperiodic time measure ment is a function of the circadian system (Saunders, 1998;Vaz Nunes & Saunders, 1999). Recently, Veerman (2001) suggested that downstream events, such as syn thesis of a clock substrate, are under circadian control in insects and mites.…”

Cross generation plasticity in cold hardiness is associated with diapause, but not the non-diapause developmental pathway, in the blowfly, Calliphora vicina

“…Obligatory diapause occurs at a specific stage in the life cycle irrespective of prevailing environmental conditions, while facultative diapause is induced following detection of specific environmental cues (Denlinger, 2002). The dominant induction cue is day length (photoperiod), which has provided a robust indicator of approaching winter conditions throughout evolutionary time (Saunders, 1997;Saunders, 2013). Induction occurs during a sensitive stage in the life cycle, and the critical day length (CDL) denotes a photoperiod that induces 50% diapause within a population (Tauber et al, 1986).…”