Adult Djungarian hamsters (Phodopus sungorus) exhibit multiple reproductive and thermoregulatory adjustments to a short day photoperiod. However, some individuals in the laboratory population fail to use this photoperiod information. Since photoperiod time measurement in mammals has a circadian basis, the applicant examined short day sensitive (=responders) and insensitive (=nonresponders) individuals to determine if differences in circadian function exist between these phenotypes. Under constant environmental conditions we found 4 differences in circadian function in the nonresponders. As a group they exhibited: 1) a longer free running period under DD, 2) a shorter duration of activity, 3) a phase response curve which has few phase delays, and 4) less 'splitting' in their activity rhythm under LL. He has also established that there is a genetic basis for these phenotypic differences and has developed genetic lines to understand which aspects of circadian organization are critical for proper photoperiod time measurement. The first experiment examines between line difference in circadian function under constant environmental conditions, while the second emphasizes entrainment to non-24 h light: dark cycles.
