Photoperiod and circadian rhythmicity in testicular response of the tree sparrow

Abstract

Investigation on the mechanism of photoperiodic time measurement in regulation of reproduction was done on the male tree sparrows (Passer montanus). Photosensitive sparrows were divided into three different groups (one control and two experimental). They were photostimulated by subjecting them to artificial long days, i.e. 14L/10D for 30 days. The control group was continued under 14L/10D while the experimental groups were transferred to either short days (9L/15D) or continuous darkness (DD) for another 30 days. Observations at 10-day intervals revealed that the birds of control group continued testicular growth. Gonadal growth did not persist, and regression was observed upon transfer of photostimulated birds of experimental groups to 9L/15D or DD. Further, there was no significant difference in the testicular volume of the birds under DD and 9L/15D. These results clearly suggest the involvement of an endogenous circadian rhythm in photoperiodic gonadal responses of the tree sparrow and are consistent with the Bunning hypothesis. They are also in agreement with the avian external coincident model of photoperiodic time measurement.

Keywords:

• circadian rhythm
• photoperiod
• tree sparrow
• testicular volume

Acknowledgement

Financial support through DST grant to A.S.D. from the Department of Science and Technology of the Government of India, New Delhi, is gratefully acknowledged.