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

The terrestrial isopod Porcellio albinus 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. Porcellio albinus 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

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

The terrestrial isopod Porcellio albinus 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. Porcellio albinus 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

Reproductive traits of Porcellio variabilis Lucas, 1946 (Isopoda, Oniscidea) from Tunisia

The breeding phenology and reproductive strategies of Porcellio variabilis were investigated, both in field and laboratory, in the population of Béja (North of Tunisia). P. variabilis Lucas, 1946 is characterized by a seasonal reproduction period followed by a sexual rest phase during November, December and January. Mean fecundity showed a great seasonal variation ranging between 29.612 eggs for females caught in the late summer, and 125.920 eggs for those collected in the spring. P. variabilis is an iteroparous species; females were able to produce one (95% of females), two (40% of females) or three broods (20% of females) during their reproduction period. The duration of the gestation period ranged from 34 days in the first brood to 14 days in the third one. Energy allocated to reproduction decreased from the first brood (26.29%) to the last one (4.618%). During the sampling period, eight cohorts were identified, each exhibiting a variable life span estimated around 6 months for cohorts born in early spring, and 12 months for those born in the fall. According to our present results and previous studies in another population of P. variabilis in Tunisia, we discuss factors of variability in breeding phenology in this species