ABSTRACT
Entrainment of circannual rhythms of body mass and reproduction was monitored for 3 years in female golden-mantled ground squirrels maintained in a simulated natural photoperiod. Both pinealectomized and pineal-intact squirrels generated circannual rhythms of body mass and estrus, but only the intact animals entrained these rhythms to a period of 365 days. In the second and third years after treatment, the period of the body mass rhythm was significantly shorter than 365 days for pinealectomized squirrels, and variance in tau among these animals was significantly greater than for intact squirrels. A similar pattern was evident in the rhythm of reproduction, which was phase-disrupted in pinealectomized squirrels but entrained in intacts. Seasonal changes in duration of nocturnal melatonin secretion by the pineal appear to be necessary to produce phase-delays required to entrain the circannual clock to a period of 12 months.
Subject(s)
Light , Pineal Gland/physiology , Sciuridae/physiology , Seasons , Animals , Body Weight/physiology , Female , Melatonin/blood , Osmolar Concentration , Photoperiod , Reproduction/physiology , Reproduction/radiation effects , Sciuridae/bloodABSTRACT
Body weights of pallid bats collected in the field were substantially greater during October and December than between April and September. When maintained in the laboratory under constant conditions of photoperiod and temperature, bats manifested circannual rhythms in body weight. These endogenous cycles were observed in adult and juvenile individuals of both sexes and in bats housed in long or short photoperiods (14 or 10 h of light/day). The period of the cycle averaged 10 mo. Photoperiod influenced the timing and magnitude of the body weight cycle; bats kept in short photoperiods achieved peak body weights earlier than animals housed in long day lengths. We propose that day length is one of the proximate factors for synchronization of circannual cycles of pallid bats.
