Diel activity patterns of the desert carabid beetle Thermophilum (=Anthia) sexmaculatum F. (Coleoptera: Carabidae)

Abstract

The diel activity patterns of two subspecies of the desert carabid beetle Thermophilum sexmaculatum from the northern and southern regions of the Sahara desert were studied in the laboratory by means of actograph experiments. It can be assumed that the species has spread from the south to the north. Simulations of seasonal climatic conditions proved that the northern subspecies T. s. sexmaculatum adapts to seasonal changing climatic conditions by shifting the main activity phase within the 24 h period. The plasticity of the distribution of diel activity seems to have enabled the border regions of the northern Sahara to be colonized. Observations in their natural habitats agree with the experimental results: it depends on season whether the northern subspecies is diurnal or nocturnal, whereas the southern subspecies T. s. marginatum is strictly nocturnal throughout the year. Diel rhythmic activity is controlled by endogenous circadian clocks in both subspecies. Environmental light–dark and temperature cycles modify the activity considerably. Both subspecies on the whole display the same activity patterns. T. s. marginatum shows greater preference for coolness and dark than does T. s. sexmaculatum.