Thyroidectomy of adult Spotted munia ( Uroloncha punctulata) leads to the gonads remaining permanently in full breeding condition and is responsible for an early increase in testis size and activity in juvenile birds. These effects may be due to (i) general disturbances in metabolism or (ii) continuous secretion of gonadotropic hormones from the hypophysis or (iii) to both of these processes.
When black-headed Munia, Munia malacca malacca, were subjected to different photoperiods, testes started developing practically immediately under constant short (8 or 9 hrs.) days, but after a delay of three months under long (15-hr.) photoperiod. Under both the photoperiods, gonads were maintained permanently in a full breeding condition. Under natural photoperiod, tests began to grow six months later than those of short-day brids and attained their maximal size four months after their recrudescence. However, thereafter they showed a rapid regression in size. It is suggested that while day-length may induce gonadal development, in nature, some other environmental factor(s) is responsible for bringing about annual gonadal regression.
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