Long Days and Thyroxine Program American Tree Sparrows for Seasonality: Evidence for Temporal Flexibility of the Breeding Season of Euthyroid Females

Wilson, Fred E.; Reinert, Bryan D.

doi:10.1006/gcen.1998.7184

Cited by 19 publications

(6 citation statements)

References 37 publications

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“…After prolonged exposure to long days, however, GnRH immunoreactivity may decrease substantially in cells and axonal fi bers with the development of photorefractoriness in some species [Dawson et al, 1985;Foster et al, 1987;Hahn and Ball, 1995;Deviche et al, 2000] but not others [Foster et al, 1988;Bentley et al, 2003]. Decreases in overall GnRH content of the brain, as determined by radioimmunoassay between photosensitive or photostimulated and photorefractory phases, are consistent with this pattern in species that show large changes in immunoreactivity [Nicholls et al, 1988;Bluhm et al, 1991;Dawson, 1998;Wilson and Reinert, 1999;Dawson et al, 2002]. Because photorefractoriness might be the most important means of controlling the duration of reproductive responsiveness and length of the breeding season at high latitudes, we expected differences in the extent to which photo-induced inactivation of the hypothalamic-pituitary-gonadal axis is manifested through reductions in GnRH, and that these differences might correspond to differences in the capacity for reproductive fl exibility Hahn et al, 1997;Dawson et al, 2001].…”

Section: Effects Of Long Days On Gnrh Immunoreactivitysupporting

confidence: 60%

“…Although molt was well underway in this individual, its gonads remained large and in this respect its response to long days was more similar to that of a photostimulated bird, with suffi cient GnRH release to elicit high plasma LH levels and to maintain an active reproductive system. The existence of 'unusual' responses such as this in individuals of other species including the American tree sparrow [Wilson and Reinert, 1999] and European starling [Dawson, 1991a] which unequivocally develop absolute photorefractoriness may, like the responder/non-responder populations of deer mice and voles [Desjardins et al, 1986;Nelson, 1987], refl ect the presence of potentially heritable natural variation in the GnRH system. Phenotypic differences in photoresponsiveness, persistence of photosensitive and photostimulated states and the associated extent to which GnRH synthesis, storage and release are modulated over extended periods of the year could be selected for as long as birds able to take advantage of resources outside of the normal window for breeding produce more progeny than those in which inactivation of the GnRH system precludes a reproductive response.…”

Section: Evolutionary Signifi Cance Of Individual Variability In Respmentioning

confidence: 99%

“…Interestingly, many passerines that terminate reproduction through absolute photorefractoriness appear to pass through a transitional period of relative refractoriness after prolonged photostimulation, but before absolute refractoriness to long days develops. These include the house sparrow [Dawson, 1991b;Hahn and Ball, 1995], the aforementioned song sparrow [Wingfi eld, 1993], American tree sparrow [ Spizella arborea ;Wilson and Reinert, 1999], and European starling [ Sturnus vulgaris ;Dawson, 2001]. As photoresponsiveness declines in these species, there may be a brief period during which gonadal regression can be accelerated by shortening the day length or temporarily arrested by exposure to very long day lengths or constant light.…”

Section: Effects Of Long Days On Gnrh Immunoreactivitymentioning

confidence: 99%

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Interspecific Variation in Photo-Induced GnRH Plasticity among Nomadic Cardueline Finches

2005

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Changes in response to photoperiod are of fundamental importance to seasonal cycles in avian reproductive development. In this study we present data on photo-induced changes in gonadotropin-releasing hormone (GnRH) immunoreactivity associated with the development of photorefractoriness in males of 3 closely related species of cardueline finch: common redpoll (Carduelis flammea), pine siskin (C. pinus) and white-winged crossbill (Loxia leucoptera). All are nomadic, mid- to high-latitude breeders with varying levels of reproductive flexibility: redpolls are typically seasonal, pine siskins more flexibly seasonal and white-winged crossbills temporally opportunistic. Males were exposed to either long (20L:4D) or short days (5L:19D), beginning in January, and GnRH was assessed via immunocytochemistry 4.5 months later. Plasma LH, testis size, and molt score were also measured. Significant reductions in the number of irGnRH cells detected, cross-sectional cell area and optical density of these cells occurred in both redpolls and siskins on long, as compared with short, days. These decreases in irGnRH, coupled with spontaneous testicular regression and onset of molt were consistent with the development of absolute photorefractoriness on constant long days. In contrast, the tendency for numbers of GnRH immunopositive cells and mean measures of GnRH immunoreactivity (cell area, optical density and axonal fiber density) to decrease were much more moderate in white-winged crossbills held on long versus short days. Although none of the four measures of GnRH immunoreactivity differed significantly between treatments in crossbills, significant shifts in the frequency distribution of irGnRH neurons to include greater numbers of less immunoreactive cells suggested that antigenic GnRH content was reduced in many cells. These photo-induced shifts in optical densities of GnRH cells in long-day, as compared with short-day crossbills followed, to a lesser extent, the pattern in pine siskins and common redpolls. For all three species, patterns of decrease in GnRH immunoreactivity, gonadal regression and molt suggest that some form of refractoriness to photostimulation develops on constant long days. However, more moderate tendencies for GnRH immunoreactivity to decrease in white-winged crossbills, coupled with limited gonadal regression and molt on long days suggest that absolute photorefractoriness might develop more slowly in this taxon than in others, or alternatively, a condition arises that is more similar to relative photorefractoriness. These data indicate that relatively small differences in the response of the neuroendocrine system to stimulatory cues such as day length may lead to remarkably different capabilities for reproductive flexibility even within a closely related family of birds.

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Section: Effects Of Long Days On Gnrh Immunoreactivitysupporting

confidence: 60%

Section: Evolutionary Signifi Cance Of Individual Variability In Respmentioning

confidence: 99%

Section: Effects Of Long Days On Gnrh Immunoreactivitymentioning

confidence: 99%

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Interspecific Variation in Photo-Induced GnRH Plasticity among Nomadic Cardueline Finches

2005

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“…The pineal gland, which exerts strong antigonadal influence in mammals (Gorman et al, 2001;Zucker, 2001) and the tropical baya weaver (Balasubramanyam and Saxena, 1973), does not seem to be involved (ChandolaSaklani et al, 1988(ChandolaSaklani et al, , 1990bPant and Chandola-Saklani, 1993). Thyroid hormones have been shown to exert inhibitory effects on gonadal development and photoneuroendocrine response in passerine birds, including the spotted munia (Chandola et al, 1974;Chaturvedi and Thapliyal, 1979;Dawson et al, 2001;Follett and Nicolls, 1988;Kar and Chandola, 1985;Pant and Chandola-Saklani, 1995;Thapliyal, 1978;Wilson and Reinert, 1999). Results of experiments being reported elsewhere (Chandola-Saklani et al, 2004) indicate that brief exposure to thyroxine in the winter can phase-shift the breeding phase so as to coincide with the monsoon period in spotted munia held in LL.…”

Section: Reprintsmentioning

confidence: 82%

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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“…Nicholls et al (1988) and Wilson (1997) suggested that both the stimulation of reproduction and subsequent programming of PR occur by the interaction of thyroid hormones and long day length early in photostimulation. This model, developed using starlings and tree sparrows, suggests that PR is programmed by the interaction of thyroxine and long days (Nicholls et al, 1988;Wilson and Reinert, 1999;Dawson, 2001;Wilson, 2001;Mishra et al, 2004) and that programming occurs as early as 1d (Dawson, 2001) or 7d (Dawson et. al, 1985) but within a few weeks of long day exposure.…”

Section: Introductionmentioning

confidence: 98%

Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens

Siopes

Proudman

2009

Poultry Science

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In addition to inducing egg production, exposure to long days concomitantly activates processes that eventually result in photorefractoriness (PR) and cessation of egg production. Experiments were conducted to evaluate the duration of exposure to long days that result in these processes. In each of 3 experiments, we subjected Large White turkey breeder hens to long days (16 or 18 h per day) for differing lengths of time from initial photostimulation and then returned them to a photoperiod (12L:12D) that provided sufficient, but decreased, photoperiodic drive to support egg production but not induce PR. Photoresponsiveness was then evaluated by egg production after a return to a longer day length (20 h per day) late in the lay period and beyond the mean onset of PR typical for these turkey hens. Hens that have undergone any reduction in photoresponsiveness should not increase egg production in response to the increased photoperiod. From experiments 1 and 2, exposure to long days for as little as 1 d and as much as 9 wk from initial photostimulation did not result in an alteration in subsequent photoresponsiveness. This was based on an increased egg production response to a change in photoperiod from 12L:12D to 20L:4D after 20 wk of photostimulation that was similar to controls held continuously on 12L:12D and opposite to the response of controls held continuously on 18L:6D. It was clear that PR had been fully programmed by 20 wk of exposure to long days. Exposure to long days for 12 wk (experiment 3) resulted in a partial alteration of subsequent photoresponsiveness. It was concluded that programming of PR during late spring-summer season occurs after 9 wk of long day exposure, is not fully expressed by 12 wk of long days, and can be fully expressed by 20 wk of photostimulation.

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Long Days and Thyroxine Program American Tree Sparrows for Seasonality: Evidence for Temporal Flexibility of the Breeding Season of Euthyroid Females

Cited by 19 publications

References 37 publications

Interspecific Variation in Photo-Induced GnRH Plasticity among Nomadic Cardueline Finches

Interspecific Variation in Photo-Induced GnRH Plasticity among Nomadic Cardueline Finches

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

Exposure duration to long day lengths associated with the expression of photorefractoriness in turkey breeder hens

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