Circadian Organization in Hemimetabolous Insects

Abstract

ABSTRACT-The circadian system of hemimetabolous insects is reviewed in respect to the locus of the circadian clock and multioscillatory organization. Because of relatively easy access to the nervous system, the neuronal organization of the clock system in hemimetabolous insects has been studied, yielding identification of the compound eye as the major photoreceptor for entrainment and the optic lobe for the circadian clock locus. The clock site within the optic lobe is inconsistent among reported species; in cockroaches the lobula was previously thought to be a most likely clock locus but accessory medulla is recently stressed to be a clock center, while more distal part of the optic lobe including the lamina and the outer medulla area for the cricket. Identification of the clock cells needs further critical studies. Although each optic lobe clock seems functionally identical, in respect to photic entrainment and generation of the rhythm, the bilaterally paired clocks form a functional unit. They interact to produce a stable time structure within individual insects by exchanging photic and temporal information through neural pathways, in which serotonin and pigment-dispersing factor (PDF) are involved as chemical messengers. The mutual interaction also plays an important role in seasonal adaptation of the rhythm.

Co-localization and unique distributions of two clock proteins CYCLE and CLOCK in the cephalic ganglia of the ground cricket, Allonemobius allardi

“…Hemimetabolous insects, such as cockroaches and crickets, have served as good experimental animals because of their relatively large nervous system with identifiable neurons that allow the search for neuronal components of the circadian system in the central nervous system (for a review, see Tomioka and Abdelsalam 2004). For locomotor rhythms, the OL has been recognized as the locus of the circadian pacemaker in cockroaches (Nishiitsutsuji-Uwo and Pittendrigh 1968) and crickets (Sokolove 1975;Tomioka and Chiba 1984;Abe et al 1997), mostly based on surgical experiments that remove, transect, or extirpate the brain structure.…”

Post-Embryonic Development of Circadian Oscillations Within and Outside the Optic Lobe in the Cricket,Gryllus bimaculatus

“…In the cricket, the clock tissue has been identified and the photoreceptor for entrainment has also been clarified with neurobiological techniques (Tomioka and Abdelsalam, 2004). Recent molecular studies have revealed that the cricket clock oscillates with cyclical expression of clock genes, as has been suggested for other insect species, but has some unique features as well (Moriyama et al, 2008;Danbara et al, 2010;Moriyama et al, 2012;Uryu et al, 2013).…”

“…They show clear behavioral rhythms with seasonal modulations and clear photoperiodic responses (Tomioka and Abdelsalam, 2004). Some of these are suitable for surgical manipulation due to their large size, and have been used for search for the circadian clock that drives the physiological rhythms and for the photoreceptors that are necessary for the clock to synchronize with environmental light cycles.…”

The ocelli of Archaeognatha (Hexapoda): Functional morphology, pigment migration and chemical nature of the reflective tapetum

“…Ocelli apparently only play a minor role in circadian entrainment (Saunders, 1976;Rieger et al, 2003;Tomioka and Abdelsalam, 2004), although nothing is known about this topic in Archaeognatha. Likewise, there is no information on whether the ocelli in Archaeognatha are involved with navigational behaviors, as in ants (Schwarz et al, 2011a,b).…”