Circadian clock controlling egg hatching in the cricket (Gryllus bimaculatus)

Mt. Itoh et Y. Sumi, Circadian clock controlling egg hatching in the cricket (Gryllus bimaculatus), J BIOL RHYT, 15(3), 2000, pp. 241-245
Citations number
Categorie Soggetti
Journal title
ISSN journal
0748-7304 → ACNP
Year of publication
241 - 245
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Adult crickets (Gryllus bimaculatus) were maintained under a 12-h light:12- h dark cycle (LD 12:12). After oviposition, their eggs were incubated under different lighting regimens at 23 degrees C, and temporal profiles of egg hatching were examined. When the eggs were:incubated in LD 12:12 or in DL 1 2:12 with a phase difference of 12 h from LD 12:12, throughout embryogenesi s, 88% to 97% of hatching occurred within 3 h of the dark-light transition on days 17 and 18 of embryogenesis; the phases of the egg-hatching rhythms in the LD 12:12 and DL 12:12 groups differed by about 12 h. In eggs incubat ed in constant darkness (DD) throughout embryogenesis, a circadian (about 2 4 h) rhythm of hatching was found, and the phase of the rhythm was similar to that seen in eggs incubated in LD 12:12, but not DL 12:12, throughout em bryogenesis. When eggs that had been incubated in DD after oviposition were transferred to DL 12:12 in the middle or later stages of embryogenesis and were returned to DD after three cycles of DL 12:12, the rhythm of hatching synchronized (entrained) to DL 12:12. However, when eggs in the earlier st ages of embryogenesis were transferred from DD to DL 12:12 and returned to DD after three cycles, 52% to 94% of hatching did not entrain to DL 12:12. To determine whether photoperiodic conditions to which the parents had been exposed influenced the timing of egg hatching, adult crickets were maintai ned in DL 12:12, and their eggs were incubated in LD 12:12, DL 12:12, or DD throughout embryogenesis. The egg-hatching rhythm was also found in the eg gs incubated under these three lighting regimens. In DD, the phase of the r hythm was similar to that seen in eggs incubated in DL 12:12, not LD 12:12, throughout embryogenesis. The results indicate that in the cricket, the ti ming of egg hatching is under circadian control and that the circadian rhyt hm of hatching entrains to 24-h light:dark cycles, but only if the light:da rk cycles are imposed midway through embryogenesis. Therefore, by midembryo genesis, a circadian clock has been formed in the cricket, and this is entr ainable to light:dark cycles. In addition, the photoperiodic conditions to which the parents (probably the mothers) have been exposed influence the ti ming of hatching, suggesting that maternal factors may regulate the timing of egg hatching.