Reproductive Phase Dependent Photosensitivity of Gonad and Pineal Gland of a Short-Nosed Fruit Bat, Cynopterus sphinx

Abstract

Photoperiodic sensitivity of gonad in relation to pineal gland activity was noted during two important reproductive phases i.e. reproductively active (February- March) and inactive (July- August) phases of nocturnal flying mammal, Cynopterus sphinx of Indian tropical origin. They were exposed to experimental long (Light: Dark in hours; 16L: 8D) and short (8L: 16D) photoperiods for 30 days during both the reproductive phases. Exposure to the long photoperiod (LP) during reproductively active phase had no significant effect on pineal gland, gonad and its hormonal concentration. However, exposure to short photoperiod (SP) induced a decrease in gonadal activity and increase in pineal activity (as judged by the gland weight, histology, low level of estradiol / testosterone and high level of melatonin in plasma). Increased melatonin and decreased estrogen levels following the short photoperiod exposure caused abortion in females, which were undergoing delayed embryonic development during reproductive inactive phase. Exposure to LP during reproductively inactive phase reactivated the gonadal axis and inhibited the pineal activity (as judged by the gland weight, histology, high level of estradiol / testosterone and low level of melatonin in plasma), while exposure to SP had no significant effect on pineal and gonad during this phase.From these observations, it is suggested that depending upon the reproductive status, short and long photo-period affected differently the gonadal and pineal gland activity of this bat. SP induced gonadal regression during reproductive active phase and LP reactivated the gonadal axis during reproductive inactive phase. Under experimental condition the inverse relationship between pineal and gonadal activity was maintained as observed in nature.