Daily and seasonal time partitioning in surface activity of Porcellioalbinus (Isopoda, Oniscidea) in the arid region of Zarat (Gabes, Tunisia)

The terrestrial isopod Porcellioalbinus is a burrowing species, dwelling in the desert of south Tunisia. Field studies were carried out in the coastal area of Zarat, Tunisia, to examine the surface activity rhythm of P.albinus in relation to daily and seasonal variations in environmental conditions. The activity of P.albinus was followed once a month, from November 2012 through October 2013. Hourly capture frequency was compared across the different seasons of the year. Porcellioalbinus is a strictly nocturnal species showing a nycthemeral rhythm regulated by the rhythmic and natural variations of the duration of the dark period. A positive correlation is observed between the circadian rhythm of the locomotor activity of the species and the duration of the dark period outside its burrow, P.albinus has a single daily activity peak. Individuals concentrated their activity in the first part of the night in winter and in the second part in summer. This peak is more spread out in spring and autumn. The differences in the activity rhythm of P.albinus between different seasons may be determined by two important factors, namely temperature and the length of the dark period.