Metabolic correlates in the working of an insect putative photoperiodic clock

Abstract

Analysis of the formal properties of photoperiodic systems has emphasized the importance of two discrete phases of nocturnal light sensitivity (the so-called points A and B) in a variety of taxa. This has been exemplified in the lepidopteran, Pieris brassicae, among other species, since the illumination of either of these phases in an otherwise short-day cycle (diapause inducing) gives rise to a long-day effect (development without diapause). In this species, the photoreceptor of diel cycles and the clock-counter system are very likely brain located. Using cytochrome oxidase activity as a marker of energy metabolism, a neuroanatomical base in the brain involved in long-day responses elicited by light at points A and B was investigated.Present results reveal that (i) the level of energy metabolism in the optic centres is connected with the photoperiodic process, and (ii) the two points A and B can be discriminated at a functional level.Referring to the formal models, the possible function of the optic centres, either as a photoreceptor or as a (part of the) clock, is discussed.

Melatonin synthesis in the optic lobes and midbrain of the grasshopper Oedipoda caerulescens

“…In summary, in the optic lobes of O. caerulescens , variations in the 5‐HT‐MEL system that follows a daily rhythm are clearly observed. There are recognized data indicating the existence of circadian pacemakers in the optic lobes of hemimetabolous insects (Chiba & Tomioka, ; Lavialle & Dumortier, ; Loher, ; Roberts, ; Sokolove, ; Stengl & Homberg, ; Tomioka & Chiba, ). Taken together, these facts bring forward the possibility that the variations of MEL in the optic lobes may function as a photoperiodic clock output in the O. caerulescens , as previously suggested for other insects (Freelancea et al, ; Saunders, ).…”