A study of circadian rhythms in two species of cave-dwelling Troglorhopalurus species in Brazil

 

Circadian rhythms are important for all animals including humans in governing the organisms daily activities when it comes to both physiology and activity. These rhythms are controlled by a biological clock that usually are adjusted by external stimuli like light and dark.

Cave-dwelling scorpions like members of the genus Troglorhopalurus Lourenço, Baptista & Giupponi, 2004 (Buthidae) are more or less living in the dark permanently. Priscila Emanuela de Souza and Rodrigo Lopes Ferreira have recently published an article studying locomotor behavior in two species of Troglorhopalurus when exposed to different light-dark regimes. 

Interestingly, their study show that both species were able to retain their normal circadian rhythmicity in all regimes (they were able to "keep the time"), even though this varied between the two species. This can be explained by the different degree of adaptation to cave habitats seen in the two species.

Abstract:
Circadian rhythms, typically synchronized with light–dark cycles, regulate key biological processes in surface organisms. In caves, however, the absence of light may disrupt these rhythms or promote alternative temporal patterns. We examined locomotor activity in two cave-dwelling scorpions with contrasting degrees of subterranean adaptation: Troglorhopalurus translucidus (troglobitic) and Troglorhopalurus lacrau (troglophilic). Activity was monitored under constant darkness (DD), light–dark (LD), and constant light (LL). Both species retained circadian rhythmicity, but with distinct responses: T. translucidus and T. lacrau exhibited diurnal activity under LD and changes in period under DD and LL. These findings demonstrate that circadian regulation persists in cave adapted scorpions, but its expression is shaped by evolutionary pressures, highlighting the plasticity of biological clocks in light-deprived environments.

Reference:
de Souza PE, Ferreira RL. Oscillating in darkness: Circadian rhythms of cave-dwelling scorpions. Chronobiol Int. 2025:1–8. [Subscription required for full text]