The circadian system of crayfish: A developmental approach

Abstract

Adult crayfish exhibit a variety of overt circadian rhythms. However, the physiological mechanisms underlying the overt rhythms are controversial. Research has centered on two overt rhythms: the motor activity and the retinal sensitivity rhythms of the genus Procambarus. The present work reviews various studies undertaken to localize pacemakers and mechanisms of entrainment responsible for these two rhythms in adult organisms of this crustacean decapod. It also describes an ontogenetic approach to the problem by means of behavioral, electrophysiological, and neurochemical experiments. The results of this approach confirm previous models proposed for adult crayfish, based on a number of circadian pacemakers distributed in the central nervous system. However, the coupling of rhythmicity between these independent oscillators might be complex and dependent on the interaction between serotonin (5-HT), light, and the crustacean hyperglycemic hormone (CHH). The latter compound has, up until now, not been considered as an agent in the genesis and synchronization of the retinal sensitivity rhythm.

Circadian clocks in crustaceans: identified neuronal and cellular systems

“…In the lobster H. americanus, light-entrainable circadian changes in 5-HT concentrations have been observed in both the central brain and the eyestalk (249). Changes in the circadian rhythm of 5-HT (and likely its ratelimiting enzyme tryptophan-hydroxylase; 250) during crayfish development according to a 9-12 hr rhythm have been interpreted as (i) being superimposed upon the basic circadian rhythm (248) or (ii) representing an example for an initially ultradian-like rhythmicity of, e.g., the ERG and retinal shielding pigment movements (15min to 4hrs), that about 30 days later is being replaced by circadian rhythmicity as has been shown for first instar crayfish P. clarkii (22).…”

“…Several crustacean clocks have previously been reviewed with regard to both circadian (10,(19)(20)(21)(22) and circatidal (3,4,6,8,19) rhythms, just to mention only some more recent or extensive works. Whilst ultradian rhythms have been detected in many systems (12), their functional significance has yet to be determined.…”

“…These latter cells in PO2 stages are a few hours earlier in acrophase than the CHH-ir tapetal and XOSG cells, which is suggestive of CHH being controlled by 5HT stimuli in the afternoon. However, this phenomenon appears timely reversed in juveniles, which may indicate that there is no functional connection between these systems (Figure 3B-E) (22,162,181). Daily and circadian changes in relative CHH abundance in the retina and the eyestalk ganglia are in fact negatively correlated and appear to be under different dual metabolic feedback control by circulating glucose and lactate (176).…”

Regulation of serotonin levels by multiple light-entrainable endogenous rhythms

“…In other crustaceans such as the fiddler crab Uca pugilator and the crayfish Procambarus clarkii, fluctuating serotonin levels have mostly been described for eyestalks (Fingerman and Fingerman, 1977;Fingerman et al, 1978;EscamillaChimal et al, 2001;Fanjul-Moles and Prieto-Sagredo, 2003). Castanon-Cervantes et al (1999) are the only authors to our knowledge who have assessed serotonin levels over 24·h in the brain of another crustacean.…”

Do culverts impact the movements of the endangered white-clawed crayfish?

“…This could potentially alter the behaviour and movement patterns in crayfish and act as a behavioural barrier to dispersal. It has been shown that crayfish behaviour is influenced by changes in light intensity (Fanjul-Moles and Prieto-Sagredo, 2003;Fanjul-Moles et al, 2004), and even species that live in dark caves exhibit circadian entrainment (Jegla and Poulson, 1968). Studies on potential behavioural obstacles as a result of dark culverts have, so far, unsurprisingly, focused on fish.…”