EFFECT OF PHOTOPERIOD AND TEMPERATURE ON OVARIAN CYCLE OF THE FROG RANA-TIGRINA (DAUD)

The effect of varying photoperiod regimes (LD: 20,4; 4,20; 6,18; 18,6 and 12,12) on ovarian follicular development was analysed in the frog Rana tigrina maintained at ambient and constant 30 degrees +/- 1 degre es C for 3 months. The experiments were conducted in early recrudescen t and quiescent phases. The frogs were fed guppies ad libitum on alter nate day. None of the photoperiod regimes had any effect on the ovarie s or the fat bodies, whereas exposure to constant high temperature (re gardless of photoperiod) during recrudescent phase induced production of greater number of eggs (similar to 18000 vs 13000 in controls) of o vulatory sizes (> 1400 mu m) compared to the corresponding controls ma intained at ambient temperature. Hence, ovarian mass also increased in these frogs. In the quiescent phase, high temperature merely enhanced growth of previtellogenic oocytes. In both the phases high temperatur e caused a reduction in the fat bodies over the respective controls, p ossibly due to increased metabolic activity. The above findings indica te that temperature plays a key role in the regulation of ovarian cycl e of Rana tigrina and that the photoperiodic mechanisms may not govern the annual recrudescence of ovaries in the frog. The study also shows that the frog exhibits the phenomenon of ''phenotypic plasticity'' in its reproductive behaviour by producing significantly greater number of eggs in response to elevated temperature.