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Namram S Singh - One of the best experts on this subject based on the ideXlab platform.
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circadian versus circannual rhythm in the photoperiodic programming of seasonal responses in eurasian tree sparrow passer montanus
Photochemical and Photobiological Sciences, 2020Co-Authors: Anand S Dixit, Namram S SinghAbstract:Experiments were performed on the subtropical tree sparrow (Passer montanus) to investigate whether day length, as a Proximate Factor, involves circadian rhythm in timing seasonal responses or these events are programmed by the mediation of an endogenous circannual rhythm. The experiments began from the two equinoxes, i.e. March and September, and continued for about 18 months. In each equinox, one group of wild birds of both sex was exposed to near simulated day length as it varies in nature at Shillong (Latitude 25°34′N, Longitude 91°53′E), and the other group was given a photoperiodic treatment in the reverse order corresponding to natural variation in day length from the other equinox. The birds exposed to near simulated day lengths in March and September showed gonadal, bill colour and molting responses, as observed in the wild birds in nature. Moreover, when photosensitive birds of March were given photoperiodic treatment in the reverse order (i.e., natural variation in day lengths beginning from September), they maintained their photosensitivity and responded only when they received increasing day length in the following September. However, when the photorefractory birds of September were exposed to reverse photoperiodic treatment (i.e. natural day length as it varies from March), they terminated their photorefractoriness after receiving decreasing day length in March the next year and responded when they again received increasing day length in the following September. These results strongly suggest that photoperiodic regulation of seasonal responses in the tree sparrow involves an endogenous circadian rhythm and exclude the possibility of circannual rhythm generation.
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Photoperiod as a Proximate Factor in control of seasonality in the subtropical male Tree Sparrow, Passer montanus
Frontiers in Zoology, 2011Co-Authors: Anand S Dixit, Namram S SinghAbstract:Background Most species of birds exhibit well-defined seasonality in their various physiological and behavioral functions like reproduction, molt, bill color etc. such that they occur at the most appropriate time of the year. Day length has been shown to be a major source of temporal information regulating seasonal reproduction and associated events in a number of avian species. The present study aims to investigate the role of photoperiod in control of seasonal cycles in the subtropical male tree sparrow ( Passer montanus ) and to compare its responses at Shillong (Latitude 25°34'N, Longitude 91°53'E) with those exhibited by its conspecifics and related species at other latitudes. Results Initial experiment involving study of seasonal cycles revealed that the wild tree sparrows posses definite seasonal cycles of testicular volume, molt and bill color. These cycles were found remarkably linked to annual solar cycle suggesting the possibility of their photoperiodic control. To confirm this possibility in the next experiment, the photosensitive birds were exposed to three different light-dark regimes that were close to what they experience at this latitude: 9L/15D (close to shortest day length), 12L/12D (equinox day length) and 14L/10D (close to longest day length) for 18 months. Tree sparrows showed testicular growth followed by regression and development of photorefractoriness, molting and bill color changes only under long daily photoperiods (12 L and 14 L) but not under short daily photoperiod (9 L). Birds, under stimulatory photoperiods, did not show reinitiation of the above responses after the completion of initiation regression cycle even after their exposure to these photoperiods for 18 months. This precludes the possibility of circannual rhythm generation and suggests the involvement of photoperiodic mechanism in control of their seasonal cycles. Further, replacement of body and primary feathers progressed with gonadal regression only under long days suggesting that the two high energy demanding events of reproduction and molt are phased at two different times in the annual cycle of the bird and are photoperiodically regulated. Results of the final experiment involving exposure of photosensitive birds to a variety of photoperiodic treatments (9L/15D, 10L/14D, 11L/13D, 12L/12D, 14L/10D and 16L/8D) for 30 days suggested that the light falling for 11 h or more is important in inducing testicular growth and function in this species. Conclusion These results clearly indicate that despite of small photofluctuation, subtropical tree sparrows are capable of fine discrimination of photoperiodic information and use day length as a Proximate environmental Factor to time their seasonal responses similar to their conspecifics and related species at other latitudes suggesting the conservation of photoperiodic control mechanism in them.
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Photoperiod as a Proximate Factor in control of seasonality in the subtropical male Tree Sparrow, Passer montanus
Frontiers in Zoology, 2011Co-Authors: Anand S Dixit, Namram S SinghAbstract:Background Most species of birds exhibit well-defined seasonality in their various physiological and behavioral functions like reproduction, molt, bill color etc. such that they occur at the most appropriate time of the year. Day length has been shown to be a major source of temporal information regulating seasonal reproduction and associated events in a number of avian species. The present study aims to investigate the role of photoperiod in control of seasonal cycles in the subtropical male tree sparrow ( Passer montanus ) and to compare its responses at Shillong (Latitude 25°34'N, Longitude 91°53'E) with those exhibited by its conspecifics and related species at other latitudes. Results Initial experiment involving study of seasonal cycles revealed that the wild tree sparrows posses definite seasonal cycles of testicular volume, molt and bill color. These cycles were found remarkably linked to annual solar cycle suggesting the possibility of their photoperiodic control. To confirm this possibility in the next experiment, the photosensitive birds were exposed to three different light-dark regimes that were close to what they experience at this latitude: 9L/15D (close to shortest day length), 12L/12D (equinox day length) and 14L/10D (close to longest day length) for 18 months. Tree sparrows showed testicular growth followed by regression and development of photorefractoriness, molting and bill color changes only under long daily photoperiods (12 L and 14 L) but not under short daily photoperiod (9 L). Birds, under stimulatory photoperiods, did not show reinitiation of the above responses after the completion of initiation regression cycle even after their exposure to these photoperiods for 18 months. This precludes the possibility of circannual rhythm generation and suggests the involvement of photoperiodic mechanism in control of their seasonal cycles. Further, replacement of body and primary feathers progressed with gonadal regression only under long days suggesting that the two high energy demanding events of reproduction and molt are phased at two different times in the annual cycle of the bird and are photoperiodically regulated. Results of the final experiment involving exposure of photosensitive birds to a variety of photoperiodic treatments (9L/15D, 10L/14D, 11L/13D, 12L/12D, 14L/10D and 16L/8D) for 30 days suggested that the light falling for 11 h or more is important in inducing testicular growth and function in this species. Conclusion These results clearly indicate that despite of small photofluctuation, subtropical tree sparrows are capable of fine discrimination of photoperiodic information and use day length as a Proximate environmental Factor to time their seasonal responses similar to their conspecifics and related species at other latitudes suggesting the conservation of photoperiodic control mechanism in them.
Anand S Dixit - One of the best experts on this subject based on the ideXlab platform.
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circadian versus circannual rhythm in the photoperiodic programming of seasonal responses in eurasian tree sparrow passer montanus
Photochemical and Photobiological Sciences, 2020Co-Authors: Anand S Dixit, Namram S SinghAbstract:Experiments were performed on the subtropical tree sparrow (Passer montanus) to investigate whether day length, as a Proximate Factor, involves circadian rhythm in timing seasonal responses or these events are programmed by the mediation of an endogenous circannual rhythm. The experiments began from the two equinoxes, i.e. March and September, and continued for about 18 months. In each equinox, one group of wild birds of both sex was exposed to near simulated day length as it varies in nature at Shillong (Latitude 25°34′N, Longitude 91°53′E), and the other group was given a photoperiodic treatment in the reverse order corresponding to natural variation in day length from the other equinox. The birds exposed to near simulated day lengths in March and September showed gonadal, bill colour and molting responses, as observed in the wild birds in nature. Moreover, when photosensitive birds of March were given photoperiodic treatment in the reverse order (i.e., natural variation in day lengths beginning from September), they maintained their photosensitivity and responded only when they received increasing day length in the following September. However, when the photorefractory birds of September were exposed to reverse photoperiodic treatment (i.e. natural day length as it varies from March), they terminated their photorefractoriness after receiving decreasing day length in March the next year and responded when they again received increasing day length in the following September. These results strongly suggest that photoperiodic regulation of seasonal responses in the tree sparrow involves an endogenous circadian rhythm and exclude the possibility of circannual rhythm generation.
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Photoperiod as a Proximate Factor in control of seasonality in the subtropical male Tree Sparrow, Passer montanus
Frontiers in Zoology, 2011Co-Authors: Anand S Dixit, Namram S SinghAbstract:Background Most species of birds exhibit well-defined seasonality in their various physiological and behavioral functions like reproduction, molt, bill color etc. such that they occur at the most appropriate time of the year. Day length has been shown to be a major source of temporal information regulating seasonal reproduction and associated events in a number of avian species. The present study aims to investigate the role of photoperiod in control of seasonal cycles in the subtropical male tree sparrow ( Passer montanus ) and to compare its responses at Shillong (Latitude 25°34'N, Longitude 91°53'E) with those exhibited by its conspecifics and related species at other latitudes. Results Initial experiment involving study of seasonal cycles revealed that the wild tree sparrows posses definite seasonal cycles of testicular volume, molt and bill color. These cycles were found remarkably linked to annual solar cycle suggesting the possibility of their photoperiodic control. To confirm this possibility in the next experiment, the photosensitive birds were exposed to three different light-dark regimes that were close to what they experience at this latitude: 9L/15D (close to shortest day length), 12L/12D (equinox day length) and 14L/10D (close to longest day length) for 18 months. Tree sparrows showed testicular growth followed by regression and development of photorefractoriness, molting and bill color changes only under long daily photoperiods (12 L and 14 L) but not under short daily photoperiod (9 L). Birds, under stimulatory photoperiods, did not show reinitiation of the above responses after the completion of initiation regression cycle even after their exposure to these photoperiods for 18 months. This precludes the possibility of circannual rhythm generation and suggests the involvement of photoperiodic mechanism in control of their seasonal cycles. Further, replacement of body and primary feathers progressed with gonadal regression only under long days suggesting that the two high energy demanding events of reproduction and molt are phased at two different times in the annual cycle of the bird and are photoperiodically regulated. Results of the final experiment involving exposure of photosensitive birds to a variety of photoperiodic treatments (9L/15D, 10L/14D, 11L/13D, 12L/12D, 14L/10D and 16L/8D) for 30 days suggested that the light falling for 11 h or more is important in inducing testicular growth and function in this species. Conclusion These results clearly indicate that despite of small photofluctuation, subtropical tree sparrows are capable of fine discrimination of photoperiodic information and use day length as a Proximate environmental Factor to time their seasonal responses similar to their conspecifics and related species at other latitudes suggesting the conservation of photoperiodic control mechanism in them.
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Photoperiod as a Proximate Factor in control of seasonality in the subtropical male Tree Sparrow, Passer montanus
Frontiers in Zoology, 2011Co-Authors: Anand S Dixit, Namram S SinghAbstract:Background Most species of birds exhibit well-defined seasonality in their various physiological and behavioral functions like reproduction, molt, bill color etc. such that they occur at the most appropriate time of the year. Day length has been shown to be a major source of temporal information regulating seasonal reproduction and associated events in a number of avian species. The present study aims to investigate the role of photoperiod in control of seasonal cycles in the subtropical male tree sparrow ( Passer montanus ) and to compare its responses at Shillong (Latitude 25°34'N, Longitude 91°53'E) with those exhibited by its conspecifics and related species at other latitudes. Results Initial experiment involving study of seasonal cycles revealed that the wild tree sparrows posses definite seasonal cycles of testicular volume, molt and bill color. These cycles were found remarkably linked to annual solar cycle suggesting the possibility of their photoperiodic control. To confirm this possibility in the next experiment, the photosensitive birds were exposed to three different light-dark regimes that were close to what they experience at this latitude: 9L/15D (close to shortest day length), 12L/12D (equinox day length) and 14L/10D (close to longest day length) for 18 months. Tree sparrows showed testicular growth followed by regression and development of photorefractoriness, molting and bill color changes only under long daily photoperiods (12 L and 14 L) but not under short daily photoperiod (9 L). Birds, under stimulatory photoperiods, did not show reinitiation of the above responses after the completion of initiation regression cycle even after their exposure to these photoperiods for 18 months. This precludes the possibility of circannual rhythm generation and suggests the involvement of photoperiodic mechanism in control of their seasonal cycles. Further, replacement of body and primary feathers progressed with gonadal regression only under long days suggesting that the two high energy demanding events of reproduction and molt are phased at two different times in the annual cycle of the bird and are photoperiodically regulated. Results of the final experiment involving exposure of photosensitive birds to a variety of photoperiodic treatments (9L/15D, 10L/14D, 11L/13D, 12L/12D, 14L/10D and 16L/8D) for 30 days suggested that the light falling for 11 h or more is important in inducing testicular growth and function in this species. Conclusion These results clearly indicate that despite of small photofluctuation, subtropical tree sparrows are capable of fine discrimination of photoperiodic information and use day length as a Proximate environmental Factor to time their seasonal responses similar to their conspecifics and related species at other latitudes suggesting the conservation of photoperiodic control mechanism in them.
Thierry Raclot - One of the best experts on this subject based on the ideXlab platform.
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Proximate and ultimate mechanisms underlying immunosuppression during the incubation fast in female eiders: roles of triiodothyronine and corticosterone
General and Comparative Endocrinology, 2009Co-Authors: Sophie Bourgeon, Yvon Le Maho, Thierry RaclotAbstract:Abstract: Available resources being limited, life-history theory predicts that natural selection favours the evolution of physiological mechanisms that ensure their optimal allocation between competing activities. Accordingly, to maximize their selective value, long-lived species face a trade-off between survival and reproduction. Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. However, both ultimate and Proximate Factors underlying the observed trade-off between reproductive effort and immunocompetence remain poorly documented. Using female common eiders (Somateria mollissima) as a model, it was earlier shown that acquired immunity is negatively affected during the incubation fast, while its activation has a negative impact on females' fitness. The current paper reports data about hormone (corticosterone and triiodothyronine) manipulations we designed to shed more light onto both ultimate and Proximate mechanisms contributing to explain immunosuppression in breeding female eiders. Corticosterone does not seem to be the main Proximate Factor for immunosuppression. Interestingly, the immunosuppressive effects of the tested hormones seem to be mediated by their negative effects on body mass. This lends support to the proposed link between the immune system and body fat reserves and is also in agreement with the resource-limitation hypothesis. It appears that the immnunopathology-avoidance hypothesis and the resource-limitation hypothesis are not mutually exclusive in breeding eiders. Further experiments are required to determine the relationship between body condition and immunocompetence during the incubation fast in long-lived birds.
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Proximate and ultimate mechanisms underlying immunosuppression during the incubation fast in female eiders: roles of triiodothyronine and corticosterone.
General and Comparative Endocrinology, 2008Co-Authors: Sophie Bourgeon, Yvon Le Maho, Thierry RaclotAbstract:Available resources being limited, life-history theory predicts that natural selection favours the evolution of physiological mechanisms that ensure their optimal allocation between competing activities. Accordingly, to maximize their selective value, long-lived species face a trade-off between survival and reproduction. Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. However, both ultimate and Proximate Factors underlying the observed trade-off between reproductive effort and immunocompetence remain poorly documented. Using female common eiders (Somateria mollissima) as a model, it was earlier shown that acquired immunity is negatively affected during the incubation fast, while its activation has a negative impact on females' fitness. The current paper reports data on corticosterone and triiodothyronine manipulations designed to shed more light onto both ultimate and Proximate mechanisms involved in the control of immunosuppression in breeding female eiders. It was found that corticosterone is not the main Proximate Factor responsible for immunosuppression and that the immunosuppressive effects of both hormones may be mediated by their negative effects on body mass. These observations are consistent with the proposed link between the immune system and body fat reserves and, with the resource-limitation hypothesis for stress-induced immunosuppression. However the alternative hypothesis, the immunopathology-avoidance hypothesis cannot be discarded and the two hypotheses are not mutually exclusive in breeding female eiders.
Sophie Bourgeon - One of the best experts on this subject based on the ideXlab platform.
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Proximate and ultimate mechanisms underlying immunosuppression during the incubation fast in female eiders: roles of triiodothyronine and corticosterone
General and Comparative Endocrinology, 2009Co-Authors: Sophie Bourgeon, Yvon Le Maho, Thierry RaclotAbstract:Abstract: Available resources being limited, life-history theory predicts that natural selection favours the evolution of physiological mechanisms that ensure their optimal allocation between competing activities. Accordingly, to maximize their selective value, long-lived species face a trade-off between survival and reproduction. Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. However, both ultimate and Proximate Factors underlying the observed trade-off between reproductive effort and immunocompetence remain poorly documented. Using female common eiders (Somateria mollissima) as a model, it was earlier shown that acquired immunity is negatively affected during the incubation fast, while its activation has a negative impact on females' fitness. The current paper reports data about hormone (corticosterone and triiodothyronine) manipulations we designed to shed more light onto both ultimate and Proximate mechanisms contributing to explain immunosuppression in breeding female eiders. Corticosterone does not seem to be the main Proximate Factor for immunosuppression. Interestingly, the immunosuppressive effects of the tested hormones seem to be mediated by their negative effects on body mass. This lends support to the proposed link between the immune system and body fat reserves and is also in agreement with the resource-limitation hypothesis. It appears that the immnunopathology-avoidance hypothesis and the resource-limitation hypothesis are not mutually exclusive in breeding eiders. Further experiments are required to determine the relationship between body condition and immunocompetence during the incubation fast in long-lived birds.
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Proximate and ultimate mechanisms underlying immunosuppression during the incubation fast in female eiders: roles of triiodothyronine and corticosterone.
General and Comparative Endocrinology, 2008Co-Authors: Sophie Bourgeon, Yvon Le Maho, Thierry RaclotAbstract:Available resources being limited, life-history theory predicts that natural selection favours the evolution of physiological mechanisms that ensure their optimal allocation between competing activities. Accordingly, to maximize their selective value, long-lived species face a trade-off between survival and reproduction. Immunity is hypothesized to share limited resources with other physiological functions and this may partly account for the fitness costs of reproduction. However, both ultimate and Proximate Factors underlying the observed trade-off between reproductive effort and immunocompetence remain poorly documented. Using female common eiders (Somateria mollissima) as a model, it was earlier shown that acquired immunity is negatively affected during the incubation fast, while its activation has a negative impact on females' fitness. The current paper reports data on corticosterone and triiodothyronine manipulations designed to shed more light onto both ultimate and Proximate mechanisms involved in the control of immunosuppression in breeding female eiders. It was found that corticosterone is not the main Proximate Factor responsible for immunosuppression and that the immunosuppressive effects of both hormones may be mediated by their negative effects on body mass. These observations are consistent with the proposed link between the immune system and body fat reserves and, with the resource-limitation hypothesis for stress-induced immunosuppression. However the alternative hypothesis, the immunopathology-avoidance hypothesis cannot be discarded and the two hypotheses are not mutually exclusive in breeding female eiders.
Robert S. Parker - One of the best experts on this subject based on the ideXlab platform.
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The Influence of Carotenoid Acquisition and Utilization on the Maintenance of Species‐Typical Plumage Pigmentation in Male American Goldfinches (Carduelis tristis) and Northern Cardinals (Cardinalis cardinalis)
Physiological and Biochemical Zoology, 2001Co-Authors: Kevin J. Mcgraw, Geoffrey E. Hill, Riccardo Stradi, Robert S. ParkerAbstract:Abstract Birds display a tremendous variety of carotenoid‐based colors in their plumage, but the mechanisms underlying interspecific variability in carotenoid pigmentation remain poorly understood. Because vertebrates cannot synthesize carotenoids de novo, access to pigments in the diet is one Proximate Factor that may shape species differences in carotenoid‐based plumage coloration. However, some birds metabolize ingested carotenoids and deposit pigments that differ in color from their dietary precursors, indicating that metabolic capabilities may also contribute to the diversity of plumage colors we see in nature. In this study, we investigated how the acquisition and utilization of carotenoids influence the maintenance of species‐typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis). We supplemented the diet of captive goldfinches with red carotenoids to determine whether males, which are typically yellow in color, were capable of g...
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the influence of carotenoid acquisition and utilization on the maintenance of species typical plumage pigmentation in male american goldfinches carduelis tristis and northern cardinals cardinalis cardinalis
Physiological and Biochemical Zoology, 2001Co-Authors: Kevin J. Mcgraw, Geoffrey E. Hill, Riccardo Stradi, Robert S. ParkerAbstract:Abstract Birds display a tremendous variety of carotenoid‐based colors in their plumage, but the mechanisms underlying interspecific variability in carotenoid pigmentation remain poorly understood. Because vertebrates cannot synthesize carotenoids de novo, access to pigments in the diet is one Proximate Factor that may shape species differences in carotenoid‐based plumage coloration. However, some birds metabolize ingested carotenoids and deposit pigments that differ in color from their dietary precursors, indicating that metabolic capabilities may also contribute to the diversity of plumage colors we see in nature. In this study, we investigated how the acquisition and utilization of carotenoids influence the maintenance of species‐typical plumage pigmentation in male American goldfinches (Carduelis tristis) and northern cardinals (Cardinalis cardinalis). We supplemented the diet of captive goldfinches with red carotenoids to determine whether males, which are typically yellow in color, were capable of g...
