Evolution of temporal order in living organisms

Abstract

Circadian clocks are believed to have evolved in parallel with the geological history of the earth, and have since been fine-tuned under selection pressures imposed by cyclic factors in the environment. These clocks regulate a wide variety of behavioral and metabolic processes in many life forms. They enhance the fitness of organisms by improving their ability to efficiently anticipate periodic events in their external environments, especially periodic changes in light, temperature and humidity. Circadian clocks provide fitness advantage even to organisms living under constant conditions, such as those prevailing in the depth of oceans or in subterranean caves, perhaps by coordinating several metabolic processes in the internal milieu. Although the issue of adaptive significance of circadian rhythms has always remained central to circadian biology research, it has never been subjected to systematic and rigorous empirical validation. A few studies carried out on free-living animals under field conditions and simulated periodic and aperiodic conditions of the laboratory suggest that circadian rhythms are of adaptive value to their owners. However, most of these studies suffer from a number of drawbacks such as lack of population-level replication, lack of true controls and lack of adequate control on the genetic composition of the populations, which in many ways limits the potential insights gained from the studies. The present review is an effort to critically discuss studies that directly or indirectly touch upon the issue of adaptive significance of circadian rhythms and highlight some shortcomings that should be avoided while designing future experiments.

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“…O estímulo luminoso interfere nos níveis do mRNA de period1, que aumentam rapidamente após um pulso de luz, enquanto os outros componentes da maquinaria não se modificam (Field e col., 2000;Paranjpe e Sharma, 2005). Esse é, portanto, o sinal que faz o reset diário do relógio.…”

Adaptive significance of circadian rhythms ofmontiuma subgroup ofDrosophila: I – locomotor behaviour

“…It is very much needed for localization of food and mates, to escape from predators, defense of territory and even often response to stress. It is a complex behaviour sensitive to environmental changes (Paranjpe and Sharma 2005;Palaksha et al 2011). However, various aspects of locomotor behaviour are not perfectly correlated implicating different genetic mechanism underlying particular measures of activity, e.g.…”

Molecular evolution of cryptochromes in fishes

“…Circadian rhythms improve fitness of organisms in both constant and changing environments (Paranjpe and Sharma, 2005). A circadian clock system consists of three principal divisions: sensors of input signals, a central oscillator, and the output pathways (Lakin-Thomas, 2000).…”