Stable daily light regimens as inductive factors of endogenous testicular cycles in the European starling,Sturnus vulgaris

“…In many species, if birds are held on long daylengths after becoming photorefractory the gonads remain regressed indefinitely. Furthermore, in starlings (Schwab, 1970;Hamner, 1971;Schwab & Rutledge, 1975;Gwinner& Ganshirt, 1982;Dawson & Goldsmith, 1983), house sparrows, Passer domesticus (A. Dawson, unpublished results), and probably other species also, transfer to short daylengths (8 h of light/day or less) is followed by slow but marked gonadal growth.…”

mentioning

confidence: 93%

Endocrine changes associated with the termination of photorefractoriness by short daylengths and thyroidectomy in starlings (Sturnus vulgaris)

Dawson¹,

Goldsmith²,

Nicholls³

et al. 1986

Journal of Endocrinology

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When starlings (Sturnus vulgaris) are transferred from short to long days, hypothalamic content of gonadotrophin-releasing hormone (GnRH) and pituitary gonadotrophin content eventually decrease, as birds become photorefractory, to values lower than they were on short days. This implies that both should increase as photorefractoriness is terminated some time after transfer from long to short days. Further, since thyroidectomy causes termination of photorefractoriness in birds held on long days, this should also result in an increase in hypothalamic GnRH and pituitary gonadotrophin contents. This study tests these hypotheses. Male starlings were transferred from short to long days for 10 weeks, by which time they should have become photorefractory. One group of birds was then killed; blood was collected, hypothalami and pituitaries were excised, and the stage of moult and testicular weights recorded. The remaining birds were then kept on long days, transferred to short days or thyroidectomized and kept on long days. Groups of birds in each treatment group were killed and sampled 2, 8 and 14 weeks later. Hypothalamic content of GnRH, and pituitary and plasma FSH and prolactin concentrations, were measured by radioimmunoassay. In birds sampled after 10 weeks of long days, hypothalamic content of GnRH was quite low, pituitary and plasma levels of FSH were very low, testes were small and pituitary and plasma prolactin levels were high. In intact birds kept on long days, hypothalamic GnRH content decreased further and remained low. Pituitary and plasma FSH levels remained low, testes remained small and pituitary and plasma prolactin levels decreased slowly.(ABSTRACT TRUNCATED AT 250 WORDS)

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“…In other words the photo-neural interaction involved in LD entrainment perhaps sets into motion inhibitory processes that keep a check on initial gonadal growth resulting in the slow growth phase. Circannual rhythms have been demonstrated in a number of other birds, but these are expressed only under certain LD conditions and never under LL or DD (Berthold, 1974;Schwab and Rutledge, 1975; see reviews Gwinner (1986), Gwinner (1996)). Spotted munia is the only avian species in which circannual cycles have been demonstrated in LL (see Gwinner (1986)).…”

Section: Discussionmentioning

confidence: 96%

Daily Increments of Light Hours Near Vernal Equinox Synchronize Circannual Testicular Cycle of Tropical Spotted Munia

Chandola-Saklani

Thapliyal²,

Negi³

et al. 2004

Chronobiology International

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In some long-lived organisms, particularly in tropical birds and migrants that spend part of the year close to the equator, endogenous circannual rhythms have been demonstrated in seasonal events like reproduction, molt, and migration. These, like the circadian rhythms, are expressed only in constant conditions of illumination with a periodicity deviating from 1 yr. If birds followed this periodicity, they would soon be out of phase with the annual calendar and perish and, therefore, they would need to be synchronized. However, almost nothing is known as to how synchronization is achieved in birds. Herein, with the help of a suitable model, viz., the tropical spotted munia and long-term experiments conducted in series over a 5-yr period, we provide direct evidence for the first time indicating that the segment of annual photocycle with maximal rate of increase prior to vernal equinox (approximately between mid-February and mid-March) synchronizes the circannual reproductive cycle with the monsoon period of ample food supply through a phase delay. Data also indicate, contrary to the prevalent view, that birds in the tropics can perceive minor changes in day-length, that birds respond to progressive changes in day-length as distinct from responding to fixed photoperiods of particular durations, and that birds can actually distinguish the quality of the environmental signal, viz., vernal equinox from early spring, or increasing days of spring from decreasing days of autumn. The underlying mechanisms, although yet to be identified, appear to involve a gonado-inhibitory rather than the conventional gonado-stimulatory response to increasing day-length. The photoperiodic responses of spotted munia are distinctly different from that of any "long-day" birds described thus far and do not conform to the prevalent "circadian coincidence" hypothesis of photoperiodism.

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Stable daily light regimens as inductive factors of endogenous testicular cycles in the European starling,Sturnus vulgaris

Cited by 11 publications

References 35 publications

Acta : XVIII Congressus Internationalis Ornithologici, Moscow, August 16-24, 1982

Acta : XVIII Congressus Internationalis Ornithologici, Moscow, August 16-24, 1982

Endocrine changes associated with the termination of photorefractoriness by short daylengths and thyroidectomy in starlings (Sturnus vulgaris)

Daily Increments of Light Hours Near Vernal Equinox Synchronize Circannual Testicular Cycle of Tropical Spotted Munia

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