Ashish Thapliyal, Asha Chandola-Saklani & Dinesh Bhatt

Thapliyal, A., Chandola-Saklani, A. & Bhatt, D. 1999. Synchronisation of the circannual clock in tropical Spotted Munia. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 1767. Johannesburg: BirdLife South Africa.

Involvement of an endogenous circannual clock in the control of reproductive cycle has been unequivocally demonstrated in the tropical Spotted Munia, Lonchura punctulata. However, the process of its synchronisation ensuring adequate timing of reproduction is not understood. In continuous illumination (LL) the reproductive cycle of Spotted Munia free runs with a periodicity of about 10 months exhibiting, as in nature (NDL), a distinct inverse relation with the cycle of food intake. The food intake cycle was now abolished by restricting the diet to a constant (50% of the maximum) level in adult male birds held in NDL and LL. Effects on two consecutive reproductive cycles were studied (monthly testicular measurements in situ under anaesthesia). In NDL diet restriction (DR) led in both cycles to a delay in gonadal peak and regression as compared to that in ad lib controls. In LL both DR treated as well as ad lib controls showed shortened free running cycles. However, like that in NDL birds DR treatment led to a delay in gonadal peak and regression. It is clear that the observed phase shift in reproductive cycle of DR treated birds results from a resetting of the circannual oscillator for reproduction. Obviously seasonal variations in food intake may be an important component of the process of synchronisation.