Circadian Activity Rhythms in Crayfish and Some Pending Issues: A Historical Review

Among other adaptations, circadian rhythms provide crayfish with an appropriate timing to respond to daily environmental changes, such as fluctuations in light and temperature, and to maintain a coordinated temporal sequence of physiological and behavioral functions. In addition, the circadian rhythm of activity places them within their ecological communities at opportune times. In relation to this rhythm, some experiments have been re-examined, along with their results and interpretations, as well as the authors’ proposals on the mechanisms responsible for generating the rhythm under either entrained or freerunning conditions. Among these proposals are the Schallek model and the Fingerman and Lago model. During this re-examination, some issues in need of reconsideration were identified, and information was found that may prove useful for addressing them. At the end of the review, the distinctive features of this circadian rhythm of activity in crayfish are summarized, and the design of experiments aimed at advancing the understanding of the mechanisms underlying these traits is outlined. These efforts aim to improve the understanding of the mechanisms that generate and regulate this rhythm.