Circadian locomotor rhythm masked by the female reproduction cycle in cockroaches

Blattella bisignata (Brunner) and B. germanica (L.) are oviparous cockroach es with cyclic reproductive behaviour, but in B. germanica only males show circadian rhythmicity of locomotion at 28 degrees C and DD (constant darkne ss). In B. bisignata, males and virgin females cockroaches entrained by lig ht-dark cycles show free-running rhythmicity in DD, and most activities occ ur during the subjective night. Daily locomotor activities of virgin female s show cyclic changes that coincided with ovarian development. Virgin femal es also exhibit calling behaviour during the subjective night, and this sho ws a free-running rhythm. Male mate-finding locomotion and female calling b ehaviour are under circadian control, so the timing for both behaviours is synchronized. However, most mated females do not show a locomotor free-runn ing rhythm under DD conditions. Our results indicate that only mated female s could not express a circadian locomotor rhythm. Pregnancy reduces a femal e's locomotory intensity and masks the expression of a circadian locomotor rhythm. We attribute the differences in circadian locomotory rhythms betwee n these two species to their living environments and mate-finding strategie s.