Locomotor behaviour of three sympatric species Ligia italica, Armadillo officinalis and Chaetophiloscia elongata (Crustacea, Oniscidea) from Ghar El Melh lagoon (Northeast Tunisia)

Abstract

ABSTRACTThe locomotor behaviour of three terrestrial isopod species, Ligia italica, Chaetophiloscia elongata and Armadillo officinalis, were investigated in populations collected from the supralittoral zone of Ghar El Melh lagoon. Locomotor rhythms were recorded in individual animals in spring under two successive experimental regimens during 15 days. In the first 5 days, individuals were kept under light-dark cycle in phase with the natural diel cycle. During the rest of experience, animals were maintained under constant darkness (DD). Using actograms and waveforms curves, results revealed that C. elongata and A. officinalis concentrated their activity during the experimental and subjective nights showing thus a nocturnal behaviour. In these species, whatever the regimen, the most important activity peak was situated respectively in the middle of the night and around the dusk. However, L. italica was characterized by a diurnal behaviour by maintaining its activity during the experimental and subjective days. The three species exhibited a circadian rhythmicity of the locomotor activity. Under light-dark cycle, mean periods determined by periodogram analysis were appreciably similar and were close to 24 h. Under constant darkness, these periods showed a slight extension. Furthermore, individuals of A. officinalis were significantly less active under nLD cycle (4h21 ± 1h53) as well as under DD (3h48 ± 1h58). The differences in the activity patterns between species highlighted in the present study will be discussed as an adaptive strategy to respond to interspecific competitive interactions.