Abstract
Background: We recently reported that the altitude of origin altered the photic and thermal sensitivity of the circadian pacemaker controlling eclosion and oviposition rhythms of high altitude Himalayan strains ofDrosophila ananassae. The present study was aimed at investigating the effects of altitude of origin on the pacemaker controlling the adult locomotor activity rhythm ofD. helvetica.
Methods: Locomotor activity rhythms of the high altitude Himalayan (haH) strain (Hemkund-Sahib, 4,121 m above sea level) and the low altitude Himalayan (laH) strain (Birahi, 1,132 m a.s.l.) ofD. helveticawere assayed by two experiments. The first experiment examined the natural entrainment pattern in light-dark (LD) cycles at the breeding site of each strain. The second experiment examined the entrainment parameters in LD 12:12 cycles and the period of free-running rhythm in constant darkness (DD) under controlled laboratory conditions.
Results: When entrained by natural or artificial LD cycles, thehaHstrain had an unimodal activity pattern with a single peak that commenced in the forenoon and continued till evening, while thelaHstrain had a bimodal activity pattern in which the morning peak occurred before lights-on and was separated by about 4 h from the evening peak. Unimodality of thehaHstrain was retained in DD; however, bimodality of thelaHstrain was abolished in DD since the evening peak disappeared immediately after the trasfer from LD 12:12 to DD. The period of the free-running rhythm of thehaHstrain was ~26.1 h, whereas that of thelaHstrain was ~21.7 h.
Conclusion: Parameters of entrainment and free-running rhythm of the adult locomotor activity of thehaHstrain ofD. helveticawere strikingly different from those of thelaHstrain and were likely due to ecological adaptations to the prevailing environmental conditions at the altitude where the species evolved.
Methods: Locomotor activity rhythms of the high altitude Himalayan (haH) strain (Hemkund-Sahib, 4,121 m above sea level) and the low altitude Himalayan (laH) strain (Birahi, 1,132 m a.s.l.) ofD. helveticawere assayed by two experiments. The first experiment examined the natural entrainment pattern in light-dark (LD) cycles at the breeding site of each strain. The second experiment examined the entrainment parameters in LD 12:12 cycles and the period of free-running rhythm in constant darkness (DD) under controlled laboratory conditions.
Results: When entrained by natural or artificial LD cycles, thehaHstrain had an unimodal activity pattern with a single peak that commenced in the forenoon and continued till evening, while thelaHstrain had a bimodal activity pattern in which the morning peak occurred before lights-on and was separated by about 4 h from the evening peak. Unimodality of thehaHstrain was retained in DD; however, bimodality of thelaHstrain was abolished in DD since the evening peak disappeared immediately after the trasfer from LD 12:12 to DD. The period of the free-running rhythm of thehaHstrain was ~26.1 h, whereas that of thelaHstrain was ~21.7 h.
Conclusion: Parameters of entrainment and free-running rhythm of the adult locomotor activity of thehaHstrain ofD. helveticawere strikingly different from those of thelaHstrain and were likely due to ecological adaptations to the prevailing environmental conditions at the altitude where the species evolved.