Circadian function in the photoperiodic induction of testicular growth in the common indian rosefinch, Carpodacus erythrinus

Abstract

The role of circadian mechanism in the photoperiodic induction of gonadal growth was investigated using 46 individuals of a subtropical migratory finch, the common Indian rosefinch ( Carpodacus erythrinus), by means of an asymmetrical photoperiodic regime. The regime consisted of a nonstimulatory basic photophase (6 h) in combination with a scotophase, in a 24-h cycle, the scotophase being interrupted by 1 h light at temporally fixed hours. The light interruption between hours 12 and 17 after the onset of the basic photoperiod led to testicular growth, while 1 h light as a continuation of the basic photophase or as an interruption 10, 19 or 21 h after the onset of the basic photophase was not stimulatory. Results clearly indicate that the rosefinch possesses a fine time-measuring device, which involves an endogenous circadian rhythm in photosensitivity. The photosensitive phase appears between hours 12/13 and 17/18 following the onset of the first light period.