Effect of light intensity on the locomotor activity rhythm of Orchestia montagui and Orchestia gammarellus from the supralittoral zone of Bizerte lagoon (North of Tunisia)

Abstract

Locomotor activity rhythm of Orchestia montagui and Orchestia gammarellus was investigated in populations from the supralittoral zone of Bizerte lagoon. The rhythm was recorded in individual animals in spring, firstly under continuous light with two simultaneous luminous intensities (5 and 140 lux) and secondly under continuous light with four different luminous intensities (5, 35, 75, 140 lux). Thirty specimens were tested for each experiment and for each species. Results revealed that whatever the species and the luminous intensity imposed, actograms showed a clear drift to the right lengthening the circadian period day after day. On the other hand, under continuous light with different luminous intensities, circadian periods determined by periodogram analysis decreased with increasing of luminous intensity for O. montagui whereas for O. gammarellus, circadian period lengthened with increasing of luminous intensity. Concerning ultradian period, it increased with luminous intensity whatever the species studied. Moreover, the stability was important under 5 lux for O. montagui and 140 lux for O. gammarellus. In addition, the study of the mean activity times calculated for these two species showed that the most important activity of individuals was observed under 75 lux for O. montagui and under 140 lux for O. gammarellus.

Keywords:

• Lagoon
• locomotor rhythm
• Orchestia montagui
• Orchestia gammarellus
• continuous light
• luminous intensity

Acknowledgments

The study was supported by the Research Unit of Bioecology and Evolutionary Systematics (UR11ES11), Faculty of Science of Tunis, University of Tunis El Manar.