Effects of altitude on circadian rhythm of adult locomotor activity in Himalayan strains of Drosophila helvetica.

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 of Drosophila ananassae. The present study was aimed at investigating the effects of altitude of origin on the pacemaker controlling the adult locomotor activity rhythm of D. 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.) of D. helvetica were 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, the haH strain had an unimodal activity pattern with a single peak that commenced in the forenoon and continued till evening, while the laH strain 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 the haH strain was retained in DD; however, bimodality of the laH strain 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 the haH strain was ~26.1 h, whereas that of the laH strain was ~21.7 h. CONCLUSION: Parameters of entrainment and free-running rhythm of the adult locomotor activity of the haH strain of D. helvetica were strikingly different from those of the laH strain and were likely due to ecological adaptations to the prevailing environmental conditions at the altitude where the species evolved.

Altitudinal variation in the circadian rhythm of oviposition in Drosophila ananassae.

The effect of altitude on four basic properties of the pacemaker controlling the circadian rhythm of oviposition in two strains of Drosophila ananassae was determined. The high altitude (HA) strain from Badrinath (5123 m above sea level) had a low amplitude peak in the forenoon while the low altitude (LA) strain from Firozpur (179 m a.s.l.) had a high amplitude peak after the lights-off of LD 12:12 cycles. Free running periods in continuous darkness were about 22.6 and 27.4 h in the HA and LA strains, respectively. The light pulse phase response curve (PRC) for the HA strain showed a low amplitude and a dead zone of 8h; the ratio for the advance to delay region (A/D) was less than 1, while the PRC for the LA strain had a high amplitude, which was devoid of a dead zone and showed a ratio of A/D > 1. The magnitude of the delay phase shifts at CT 18 evoked by light pulses of 1 h duration, but varying light intensity was significantly different in the HA and LA strain, which suggests that the photic sensitivity of the clock photoreceptors mediating the phase shifts had been affected by the altitude.

Effects of temperature, photoperiod, and light intensity on the eclosion rhythm of the high-altitude Himalayan strain of Drosophila ananassae.

Eclosion rhythm of the high-altitude Himalayan strain of Drosophila ananassae from Badrinath (altitude 5123 m) was temperature-dependent and at 21 degrees C, it was entrained by cycles of 12h light: 12h darkness (LD 12:12) and free-ran in constant darkness, however, it was arrhythmic at 13 degrees C or 17 degrees C under identical experimental conditions (Khare, P. V., Barnabas, R. J., Kanojiya, M., Kulkarni, A. D., Joshi, D. S. (2002). Temperature dependent eclosion rhythmicity in the high altitude Himalayan strains of Drosophila ananassae. Chronobiol. Int. 19:1041-1052). The present studies were designed to see whether or not these strains could be entrained at 13 degrees C, 17 degrees C, and 21 degrees C by two types of LD cycles in which the photoperiod at 100 lux intensity varied from 6h to 18h, and the light intensity of LD 14:10 cycles varied from 0.001 lux to 1000 lux. All LD cycles entrained this strain at 21 degrees C but not at 13 degrees C or 17 degrees C. These results demonstrate that the entrainment of eclosion rhythm depends on the ambient temperature and not on the photoperiod or light intensity of LD cycles. Thus the temperature has taken precedence over the light in the entrainment process of eclosion rhythm of the high altitude Himalayan strain of D. ananassae. This may be the result of natural selection in response to the environmental temperature at Badrinath that resembles that of the sub-Arctic region but the photoperiod or light intensity are of the subtropical region.