ADJUSTABILITY OF THE CIRCADIAN CLOCK IN THE COCKROACHES: A COMPARATIVE STUDY OF TWO CLOSELY, RELATED SPECIES,BLATTELLA GERMANICAANDBLATTELLA BISIGNATA

Abstract

A single 2h light pulse (250 lux) was given at various times to phase shift the locomotor circadian rhythm of two species of closely related cockroaches, Blattella bisignata and Blatella germanica. The phase-response curve (PRC) of both species showed a similar pattern. Phase delays and advances were induced by light pulse during the early and late subjective night, respectively, while no clear phase shifting was elicited during the subjective day. However, the magnitude of the phase delay (1.89h +/- 0.66h) and advance (0.69h +/- 0.36h) of B. bisignata was significantly larger than that of B. germanica (0.78h +/- 0.38h and 0.35h +/- 0.18h, respectively). This result indicates the superior adjustability of the circadian clock in B. bisignata. The period-response curve (PdRC) was also constructed for both species. Although both species did not show great flexibility in circadian period changes, the phase shifts were significantly correlated with the period changes in the advance zone of B. bisignata (r = 0.72, P < .1). This allowed the circadian clock of B. bisignata to display better entrainability since the phase advance adjustment was significantly more difficult than that of phase delay. The results indicate the overall adjustability of the circadian clock of B. germanica is inferior to that of B. bisignata. The significance of this finding is discussed from an ecological perspective.

Adaptation of the cockroachBlattella germanicato human habitats: circadian and noncircadian factors

“…A phase advance or delay of locomotor activity has been observed in crickets, sparrows and kowaris because of the intrusion of a light pulse during (subjective) night time (Binkley & Mosher, ; Kennedy et al , ; Okada et al , ). In cockroaches, tests of locomotor response to light pulses (2 h per pulse) show that B. germanica is more resistant to the pulse interference than B. bisignata : The maximum durations of the phase delay and phase advance of B. germanica are 4.39 and 2.51 h, respectively; in B. bisignata , however, the durations are longer at 5.98 h (delay) and 5.91 h (advance) (Wei & Lee, ). Compared with B. bisignata , B. germanica thus possesses two advantages with respect to displaying locomotor activity: (i) between cycles, it is more sensitive to the shift of light–dark cycles and (ii) within cycles, it is less sensitive to light interference in a given light–dark cycle.…”

“…(A) Sensitivity to cycle shift: male B. germanica are more efficient in responding to the changes of daily light/dark cycles. (B) Sensitivity to light pulses: male B. germanica are more resistant to the light‐pulse interference (Wei & Lee, ). (C) Female masking effects: B. germanica relies on the ovary‐dependent masking factors to feed or mate in the light phase (Lee & Wu, ; Lin & Lee, , ; Tsai & Lee, ).…”

Describing dynamics of driven multistable oscillators with phase transfer curves

“…One of practical applications is optimal re-adjustment of the phase of circadian rhythms of humans [15]. Here, the concept of PRC (sometimes one speaks on Phase Transition Curves [16][17][18]) is widely used to describe the effect of different stimuli (such as light pulses, temperature pulses, or pulses of drugs or chemicals) on the circadian rhythm. Another application is suppression of Parkinson's tremor by phase resetting [19].…”