Circadian clocks in crustaceans: identified neuronal and cellular systems

Abstract

Circadian rhythms are known for locomotory and reproductive behaviours, and the functioning of sensory organs, nervous structures, metabolism and developmental processes. The mechanisms and cellular bases of control are mainly inferred from circadian phenomenologies, ablation experiments and pharmacological approaches. Cellular systems for regulation summarised here comprise the retina, the eyestalk neuroendocrine X-organ-sinus gland system, several neuropeptides such as red pigment concentrating, hyperglycaemic and pigment-dispersing hormones, and factors such as serotonin and melatonin. No master clock has been identified, but a model of distributed clockwork involves oscillators such as the retinular cells, neurosecretory systems in the optic lobes, putative brain pacemakers, and the caudal photoreceptor. Extraretinal brain photoreceptors mediate entrainment. Comparative analyses of clock neurons and proteins known from insects may allow the identification of candidate clock neurons in crustaceans as putative homologues in the two taxa. Evidence for the existence of "insect-like" intracellular clock proteins and (light sensitive) transcription factors is scarce, but clock-, period-, and cryptochrome-gene products have been localised in the CNS and other organs rendering further investigations into crustacean clockwork very promising.

Chronic electromyographic analysis of circadian locomotor activity in crayfish

“…The circadian rhythms of locomotor activity and sensory input, in particular, have been intensively studied to clarify the neuronal mechanisms of the rhythm by using surgical interference, ablation, biochemical and molecular biological techniques [3,38,43]. Although these researches provided evidences that the circadian locomotor activity was attributed by endogenous factors functioning in the brain [3,38,43], it remained unknown how the endogenous factors affect the locomotor control system in the central nervous system. The locomotor behavior can be initiated in general either spontaneously or reflexively [44][45][46].…”

“…We demonstrated by chronic EMG recording that the locomotor behavior was initiated spontaneously, not reflexively by any external stimulus. It has been proposed that the locomotory circadian rhythmicity of P. clarkii is generated by clock proteins and regulated by hormonal and neuromodulator secretion in the brain [3,41,43] and also is regulated by photoreceptors in the brain [37,38,43] or in the 6 th abdominal ganglion [56,57]. Although the details of interaction cascades among those factors remain unknown, the brain should play an important role for the circadian locomotor activity [3,38,43].…”

“…It has been proposed that the locomotory circadian rhythmicity of P. clarkii is generated by clock proteins and regulated by hormonal and neuromodulator secretion in the brain [3,41,43] and also is regulated by photoreceptors in the brain [37,38,43] or in the 6 th abdominal ganglion [56,57]. Although the details of interaction cascades among those factors remain unknown, the brain should play an important role for the circadian locomotor activity [3,38,43]. This contribution of the brain function is consistent with our results, suggesting that the motivational system in the brain for spontaneous initiation of walking is linked with the endogenous factor for locomotory circadian rhythm.…”

“…These rhythms are thought to be endogenous [1][2][3], based on an internal clock or pacemaker that resides in a specific site in the central nervous system depending on animal species [4]. Among many kinds of behavioral rhythms, the most widely recognized in the animal kingdom is that observed in locomotor behavior including walking [5][6][7], swimming [8,9], and flying [10,11].…”

Acoustic behaviours of large crustaceans in NE Atlantic coastal habitats

“…Because many decapod crustaceans are nocturnal and therefore active during dim or twilight hours (Strauss & Dircksen 2010), each species was recorded over a 24 h cycle in addition to the shorter recording sessions. Recordings were performed as in the shorttime experiments (density, silicone plate, sound measurements) except that the crustaceans were acclimated in the recording tank for 24 h before the recording began.…”