High variability in the expression of circadian rhythms in a cave beetle population

Abstract

Cave-dwelling organisms belong to widely different evolutionary lineages but they show parallel or convergent evolution in several morphological and physiological traits such as elongated appendages, lower metabolism, specialized sensory systems, loss of eye and pigmentation. Circadian rhythms in locomotor activity have already been documented in hypogean insects but ultradian rhythmicity in cave-dwelling organisms has been reported only by recent authors. We selected Laemostenus latialis as a good candidate to investigate the biological clock functioning in a species thought to be at its beginning of the process of cave evolution in the darkness. We based our analysis on inferential methods used here to obtain the quantitative resolution of the rhythm features. An automatic electronic device was developed to this purpose so to continuously monitoring the general locomotor activity of individual cave-dwelling beetles. We found significant locomotor rhythms to be present and that Laemostenus maintained a 24-h circadian rhythm but with a different amplitude. We observed two different and opposite behavioural patterns: the "Rhythmic group" showed a typical circadian rhythmicity of surface-dwelling animals with a surprisingly and extremely stable circadian period and with a restricted variance and a high amplitude. Differently, within the "arrhythmic group" we have observed an evanescent circadian period with high variability in tau, a larger variance and a lower amplitude. DFT spectral analysis showed the presence of ultradian rhythms with several significant peaks in the range 1-10 h and a main peak at 12 h, similar to those found in mysid crustaceans, cockroaches and mice. Ultradian rhythm looked independent from the circadian one and we did not observe any regularity. Further experimental studies are still needed to track the variation of this trait along the process of adaptation to cave life, particularly in closely related populations and species of troglophilic animals. © 2014 © 2014 Taylor & Francis

Day–night and seasonal variations of a subterranean invertebrate community in the twilight zone

“…It is self-evident that the most easily detectable day-night variation in the environmental conditions of the twilight zone pertain the illuminance. Most species inhabiting the twilight zone should theoretically perceive and respond to variations in light availability within the typical circadian cycle of 24 hours -although some erratic patterns of activity have been documented (Koilraj et al 2000, Hoenen 2005, Pasquali and Sbordoni 2014. Variations in the composition of the community between day and night were indeed observed.…”

Locomotor activity rhythms in high arctic freshwater crustacean:Lepidurus arcticus(Branchiopoda; Notostraca)

“…polar regions, caves). Such animals may have evolved a mechanism to sustain prolonged activity around the clock without damage (Cavallari et al 2011;Pasquali & Sbordoni 2014). The mechanisms underlying around-the-clock activity are not well understood, but the available data suggest that several different mechanisms may lead to this extreme form of chronobiological plasticity.…”

Incipient regressive evolution of the circadian rhythms of a cave amphipod

“…Pasquali and Sbordoni (2014) and Beale and Whitman (2015) reviewed the literature and suggest that circadian activity tends to degenerate in cave obligate organisms, as indicated by comparisons of epigean and troglophilic species to troglobitic ones. However, the data have shown great variability.…”