10/28/2023 0 Comments Nocturnal animals meaning and examples![]() ![]() It is thought that the selective advantages of a clock are for optimizing the economy of biological systems, enabling plasticity of responses to an altered environment, and allowing for predictive, rather than purely reactive, homeostatic control.īy necessity and design, elucidation of circadian mechanisms has mostly relied on using model organisms that are amenable to genetic manipulation and standard laboratory housing. Variations in photic sensitivity, in concert with changes in the pacemaker's endogenous period and amplitude, can dramatically affect the phase of entrainment of clock-controlled events. The pacemaker works as a clock because its endogenous period is adjusted to the external 24 h period, primarily by light-induced phase shifts that reset the pacemaker's oscillation. Groups of autonomous single-cell oscillators are coupled together to form discrete pacemakers that generate coherent outputs for expression of overt rhythms with a diverse range of tissue-, species- and developmentally specific waveforms and phases. It is believed that genes at the clock's core function as autoregulatory feedback loops within individual cells, with oscillating levels of nuclear proteins negatively regulating the transcription of their own mRNAs. ![]() It is a layered system with emergent properties at several levels of organization, including regulatory molecules, cells, circuits and tissues. In the last few decades, there have been spectacular advances in our understanding of this clock mechanism. Central to this adaptation is the evolution of an endogenous, self-sustained, 24 h (circadian) timekeeping mechanism (‘clock’) that orchestrates body rhythms for concerted action and synchronizes (entrains) them to the local time of day. Since the dawn of life, most organisms have had to adapt to environmental cycles of light and darkness, and restrict many of their biological activities to specific times of day and night. The papers emphasize that the complexity and diversity of the natural world represent a powerful experimental resource. The seven papers in this Special Feature of Proceedings of the Royal Society B take on this challenge, reviewing the influences of moonlight, latitudinal clines, evolutionary history, social interactions, specialized temporal niches, annual variation and recently appreciated post-transcriptional molecular mechanisms. For the most part, these analyses have been carried out using model organisms in standard laboratory housing, but to begin to understand the adaptive significance of the clock, we must expand our scope to study diverse animal species from different taxonomic groups, showing diverse activity patterns, in their natural environments. Our knowledge of the circadian system of animals at the molecular, cellular, tissue and organismal levels is remarkable, and we are beginning to understand how each of these levels contributes to the emergent properties and increased complexity of the system as a whole. Daily rhythms of physiology and behaviour are governed by an endogenous timekeeping mechanism (a circadian ‘clock’), with the alternation of environmental light and darkness synchronizing (entraining) these rhythms to the natural day–night cycle.
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