Season-dependent effects of melatonin on testes and fur color in mountain hares (Lepus timidus L.).

Melatonin was administered in 3 seasons to adult male mountain hares (Lepus timidus L.) kept in long or short photoperiods. Melatonin and short photoperiods induced testis regression and fur whitening in summer and autumn but not in winter. Both treatments combined seemed to provoke an advanced onset of the refractory period.