Abstract
Adult male Blossomheaded Parakeets were held under artificial very long (22L) and very short (2L) daily pohoto periods either for 45 days or for both 45 days and 90 days during different phases of the annual gonadal cycle. These experiments were designed so as to establish: (i) whether this is at all photosensitive or not; and (ii) if photosensitive, the importance of the duration of the photoperiod in the periodic activation of the testes of the bird. Longer periods of artificial light or darkness did not affect spermatogenesis throughout the preparatory and early progressive phases (May through October) of the annual reproductive cycle. But the testes of the parakeets became precociously mature when the birds were held in long photoperiods, for 45 days, during the late progressive phase (Nov. -Jan.). The same photoperiodic regimen caused testicular involution when the treatment was extended up to 90 days. During the same reproductive phase retardation of testicular growth was attested with the studies of the birds kept in darkness for 45 days. Under identical photoschedule the occurrence of spermatogenesis was noted in a few tubules of the testes of birds held in darkness for 90 days. During the prebreeding phase (Jan. -Feb.) the testes of the long photoperiodic birds were spermatogenetically active after 45 days treatment, but regressed when the treatment was continued for 90 days. Long daily darkness periods for durations of 45 and 90 days during the same reproductive phase induced retardation of testicular growth. None of the used photoschedules, i. e. 22L 2D or 2L 22D, appeared to affect testicular regression, a time bound natural phenomenon of the free-living species, when the birds were treated for 45 days after the breeding phase (Feb. -March) of the annual gonadal cycle.
The results indicate that: (i) the duration of daily Photoperiod probably has no important role in the seasonal recrudescence of spermatogenesis, but the same factor may have certain uses in promoting further spermatogenesis in the testes of the bird; (ii) influence of the prolonged duration of very long stimulatory photoperiod is inhibitory to the testicular functions of this species; (iii) artificial long or short days cannot affect the periodic testicular involution; (iv) this bird becomes photorefractory during, at least, the preparatory and early progressive phases (May- Oct.) of the annual gonadal cycle; (v) the duration of photorefractoriness is possibly not less than a period of six months. As a tentative unifying hypothesis to be tested, it may be suggested here that in case of the low-latitude male Blossomheaded Parakeets, the duration of the available photoperiod possibly constitutes part of the battery of information used in timing reproductive functions.
