Emberiza Bruniceps Research Articles

Environmental and hormonal control of vernal migration in redheaded bunting (Emberiza bruniceps)

This paper reviews the factors and mechanisms which result in the development of the metabolic state characteristic of migration with special reference to a palaeotropic migrant the redheaded bunting, Emberiza bruniceps. Changes in climatic conditions and food supply act as proximate triggers of migratory behaviour in partial migrants. Typical migrants like buntings use daylength as a cue but the exact mechanism of how photoperiodic information is translated in terms of migratory events is still not known. Almost entirely the photoperiodic effects have been explained on the basis of the involvement of hypothalamo/hypophyseal system. We feel mechanism(s) other than those acting through neuroendocrine system may be equally important. Furthermore the role of temperature has not been adequately explored so far. Our observations indicate the possibility that redheaded buntings might integrate the information received from photoperiod with environmental temperature (and other factors?) resulting in the development of migratory state. The physiological control of avian migration is much less understood. Majority of papers have centered around the 'gonadal hypothesis' of Rowan supporting or contradicting it without providing conclusive evidence. Pituitary prolactin has also been shown to be implicated although the mechanism of action is only speculative. Conclusive evidence for the involvement of thyroid hormones (thyroxine, T4; triiodothyronine, T3) in the physiological timing of migration has been produced attributing independent roles to T4 and T3. It is suggested that seasonal variation in peripheral conversion of T4 to T3 could serve as an effective strategy to render available the required thyroid hormones T4 and/or T3 during different phases of the year thus accounting for the metabolic switch over from T4-dependent moult to T3-dependent migratory fat deposition and zugunruhe and also ensuring preclusion of simultaneous occurrence of these mutually incompatible events. Considering that the number of environmental and physiological factors influence this mechanism and considering that thyroid hormone molecule has been put to a wide range of usage during the course of evolution the mechanism(s) of peripheral conversion of T4-T3 may assume great flexibility and have selective value-especially in migration which is known to have evolved several times in diverse avian families. The attractiveness of this hypothesis lies in the fact that it has potential to explain the both physiological development of the metabolic state of migration and at the same time the physiological timing of migration not only with respect to the cycle of environment but also with respect to other conflicting seasonal events (moult and reproduction).

A role for thyroid hormones in the development of premigratory disposition in redheaded bunting, Emberiza bruniceps

Excessive fat deposition and zugunruhe (nocturnal restlessness), two characteristics of premigratory disposition, are displayed in caged redheaded buntings. In earlier experiments thyroid ablation was found to inhibit premigratory fattening in this bird. Also, seasonal investigations on thyroid hormonal profiles indicated a distinct rise in circulating tri-iodothyronine just before spring migration, most likely as a result of increased peripheral monodeiodination of thyroxine. The physiological relevance of these findings has been assessed in the present paper. Results indicated that removal of thyroid gland completely prevented development of zugunruhe and fat deposition; replacement therapy with T4 or T3 restored both. Thyroxine-induced fattening in thyroidectomized birds was found to be dose responsive. In two experiments in thyroidectomized and intact birds each suppression of extrathyroidal conversion of thyroxine into triiodothyronine by iopanoic acid completely suppressed zugunruhe and fattening in thyroidectomized as well as intact birds, arguing for a role of triiodothyronine in migratory physiology. Blockage of thyroxine to triiodothyronine conversion, however, did not suppress feather regeneration, indicating that unlike effects on migratory parameters in the same individuals thyroxine-induced feather regeneration does not involve prior monodeiodination to triiodothyronine. Thus, contrary to the prevailing view that triiodothyronine alone is the finally active thyroid hormone (thyroxine being a precursor), both thyroxine and triiodothyronine may have specific roles to play in the physiology of seasonal events, and peripheral conversion of thyroxine to triiodothyronine may be one of the physiological devices to ensure that energetically incompatible events like migration and moulting do not occur simultaneously. Results also indicate that increasing spring daylengths which are known to trigger avian migration may influence peripheral conversion of thyroxine to triiodothyronine possibly imparting to this physiological process an adaptive value in the timing of seasonal events.

Interaction between serotonin and a dopamine precursor (given 8 hour apart) and luteinizing hormone alters reproductive and metabolic responses of migratory red headed bunting(Emberiza bruniceps)

Abstract During the progressive phase of the seasonal breeding cycle four groups of male buntings were treated with (i) Normal saline (control), (ii) Luteinizing hormone (LH), (iii) L‐Dihydroxyphenylalanine (L‐DOPA, a dopamine precursor) given 8 hr after 5‐Hydroxytryptophan (5‐HTP, serotonin) (8‐hr relationship) and (iv) LH and these neurotransmitter precursor drugs with the same temporal relationship (LH + 8 hr). The results indicate that at the end of the study, while the controls as well as the LH treated birds exhibited full breeding condition (although its degree of development was higher in the latter), the testes of birds of the “8‐hr group”; showed complete atrophy. But, the birds receiving both treatments (LH + 8 hr) were not different from the controls. The body weight responses of the birds followed the same pattern as those of testes weight. It is suggested that the phase relationship of serotonergic and dopaminergic drugs controls the reproductive (gonadal activity) and metabolic (body weight...

The effects of combined serotonin and dopamine precursor application during testicular photosensitivity vs photorefractoriness of the red headed bunting(emberiza bruniceps)

Abstract A study of the temporal synergism of serotonergic and dopaminergic activity in the regulation of reproductive seasonality of photosensitive and photorefractory migratory Red headed bunting was undertaken. In experiment 1, groups of birds kept in natural day length (NDL) in their photosensitive phase (April) received daily injections of L‐DOPA (L‐dihydroxyphenylalanine, a dopamine precursor) at 8 and 12 hr after 5‐HTP (5 hydroxytryptophan, a serotonin precursor) administration. One control group received two daily injections of saline. The injections with 12‐hr temporal relation induced early recrudescence and full gonadal growth was achieved much in advance to that of control birds. The applications with 8‐hr temporal relation suppressed the testicular growth initially but later on this effect was eliminated by NDL of May‐June. In Experiment 2, photorefractory birds also received the treatments but the temporal relation of 5‐HTP and L‐DOPA had no effect on the regressed gonads of these birds. This study indicates that injections with specific phase relations of dopamine and serotonin precursors may alter seasonal reproductive conditions only in the photosensitive phase but had no effect in photorefractory birds.

The effect of different temporal relationships of 5‐hydroxytryptophan (5‐HTP) and l‐dihydroxyphenylalanine (L‐DOPA) on reproductive and metabolic responses of migratory red‐headed bunting (Emberiza bruniceps)

Abstract To study the reproductive and metabolic effects of circadian serotonergic and Dopaminergic activities, 5‐hydroxytryptophan (5‐HTP, serotonin precursor) and L‐dihydroxyphenylalanine (L‐DOPA, dopamine precursor) were administered daily in different temporal relationships in Red‐headed bunting (Emberiza bruniceps) during the preparatory phase of annual gonadal cycle. L‐DOPA given daily after 12 hours of 5‐HTP injection (12‐hr relationship) induced full gonadal development and fat deposition. But, L‐DOPA given after 4 hours of 5‐HTP administration (4‐hr relationship) stimulated only fat deposition without any gonadal effect. On the other hand, these two drugs injected 8‐hour apart led to significant decrease in gonadal growth as well as fat deposition. The findings manifested that 12 hour relationship of these two neural oscillations may induce breeding conditions (summer), 8 hour relationship induced post reproductive regressive/photorefractory condition (late summer) and 4‐hour relationship induced...

Effects of corticosterone, metapyrone, and ACTH on testicular function at different stages of the breeding cycle in migratory redheaded bunting, Emberiza bruniceps

To study the seasonal reproductive responses, corticosterone (0.2 and 2 μg/day), metapyrone (0.6 mg/day), and ACTH (0.25 IU/day) were administered in male redheaded bunting, Emberiza bruniceps, during different phases of the annual gonadal cycle. All of the three treatments inhibited gonadal growth during the preparatory phase, suggesting that during the early stage of annual gonadal growth, an optimum level of the hormones of pituitary-adrenal axis is essential. In the progressive and breeding phase, while corticosterone administration had no effect, metapyrone inhibited the annual gonadal development, suggesting the necessity of increasing or increased adrenal steroid hormone during this phase. In the regressive phase, while corticosterone enhanced the rate of gonadal regression, metapyrone treatment did not allow the gonad to regress. Further, ACTH administration induced full breeding condition in the regressing gonad. It is suggested that while a higher level of adrenal steroids and a low ACTH (by exogenous corticosterone) may enhance the testicular regression, moderate levels of ACTH (caused by exogenous metapyrone) did not allow regression and increased ACTH levels (by exogenous ACTH) caused full development of the regressing gonad. Thus the sensitivity of the neuroendocrine-gonadal axis not only varies in response to photoperiod, but the reproductive system also responds differently to pharmacological administration of the above three hormones and drugs during different phases of the breeding cycle.

Role of thyroid in sexual and body weight cycles of the migratory redheaded bunting, Emberiza bruniceps

In the male redheaded bunting, Emberiza bruniceps, kept under natural lighting in northern India (Lat 25° 18′N, Long 83° 01′E), testicular growth began during March/April and full spermatogenesis was achieved in May/June; thereafter, the testes regressed and remained regressed for the rest of the year. Thyroidectomy between November and April partially suppressed photoinduced testicular growth in May/June, but did not prevent testicular regression in July. The extent to which thyroidectomy suppressed photoinduced testicular growth was directly related to the time elapsed between thyroidectomy and photostimulation. Thyroidectomy in mid-late May induced testicular regression, an effect which was reversed by daily im injection of 500–2000 ng thyroxine/bird/day/30 days. Thyroidectomy or treatment of intact or thyroidectomized birds between July and March when the testes were regressed had no immediate effect on testicular growth. Body weight which was about 24 g between December and March, increased to about 28 g during the breeding season. Thereafter, it decreased to 21–22 g between August and October. Thyroidectomy between November and May caused an immediate fall in body weight, an effect which was reversed by daily im injection of 500–2000 ng thyroxine/bird/day/30 days. Neither thyroidectomy nor thyroxine treatment prevented the seasonal fall in body weight in June and July nor affected body weight between August and October. It is suggested that in the male redheaded bunting, under natural lighting, thyroid hormones are necessary for the full development of the testes and an increase in body weight during the breeding season. However, thyroid hormones do not appear to be necessary for the development of photorefractoriness or for the seasonal decrease in body weight.

Circadian control of photoperiodic responses in a female migratory bunting ( Emberiza bruniceps)

The photoperiodic response of female redheaded bunting ( Emberiza bruniceps) was investigated in photosensitive and photorefractory birds exposed to resonance lighting cycles. Ovarian growth was stimulated in resonance cycles where light was present during the predicted photoinducible phase. Photorefractoriness was dissipated by resonance cycles in which light did not fall at times corresponding to the photoinducible phase. It is concluded that photosensitive and photorefractory female redheaded bunting monitor the photoperiodic time by means of a circadian rhythm.

Thyroid and gonadal hormones in feather regeneration of the redheaded bunting, Emberiza bruniceps

AbstractThe time lag in the appearance of the first feather papillae (rate of feather regeneration) was studied after monthly depluming of the redheaded bunting (Emberiza bruniceps). Results indicate that the rate of feather regeneration varies over an annual time scale. When a comparison was made between monthly changes in levels of plasma thyroid hormones (thyroxine‐T4 and triiodothyronine‐T3) in redheaded buntings (Pathak and Chandola, '82a) and the rate of feather regeneration, the rate of regeneration showed a distinct correlation with levels of circulating T4. The rate of feather regeneration was faster during December and June when endogenous T4 levels were high and slower during July/August and March/April when levels of circulating T4 were relatively low. Such a relationship was, however, not observed with T3. Results of administration of T4 and T3 separately, in normal as well as in thyroidectomized birds; in different doses; and during different phases of the annual cycle, indicate a strikingly greater influence of T4 on the rate of feather regeneration and on the number of regenerated papillae than T3. Injection of propylthiouracil (PTU—an effective inhibitor of peripheral conversion of T4 to T3 in the redheaded bunting) in thyroidectomized birds that were also receiving T4, resulted in even faster rates of feather regeneration. Thyroidectomized birds receiving saline had no feather regeneration. Castration led to a slow rate of feather regeneration during May/June only. During this period thyroid activity of the redheaded bunting is known to be significantly influenced by gonadal hormones; this influence is not apparent during January/February or August. Injections of testosterone neutralized the effects of castration. It is concluded that T4 is more important than T3 for feather regeneration in redheaded buntings and that the effects of castration are due to alterations in thyroid function.

Light, thyroid, gonad, and photorefractory state in the migratory redheaded bunting, Emberiza bruniceps

When exposed to constant long photoperiods the redheaded bunting, Emberiza bruniceps, was shown to become absolutely photorefractory and the condition was observed to be accelerated by thyroidectomy. Photoinduced gonadal growth was inhibited partially and the photoinduced increase in body weight was inhibited completely by throidectomy. Injection of thyroxine reversed the effects of thyroidectomy if administered during the nonbreeding photosensitive or breeding states, but had no effect in birds which had entered the photorefractory state. Gonadal growth was stimulated by pregnant mare serum gonadotropin in intact and thyroidectomized photorefractory birds, suggesting that thyroidectomy does not lead to loss of response of the gonads to gonadotrophins but directly affects the secretion of gonadotrophins. Injection of prolactin increased the body weight of intact but not of thyroidectomized photorefractory birds, suggesting that metabolic photorefractoriness is due to a decreased secretion of prolactin and that the effects of T 4 on body weight depend on its synergism with prolactin. It is suggested that thyroid hormone(s) may be part of the coupling mechanism(s) for body weight and gonad development cycles and that the beneficial role of thyroid hormones may consist in an increased threshold of the central nerous system control of neuroendocrine functions towards the negative feedback regulation of increased sex steroid levels.

Effects of exogenous prolactin on ovarian growth and fattening in the redheaded bunting, Emberiza bruniceps

Subcutaneous daily injections of ovine prolactin (PRL) inhibit photoperiodic induction of gonads and fattening in the female redheaded bunting ( Emberiza bruniceps). However, birds respond to the same photoperiod (15L:9D) after withdrawal of the exogenous PRL. Further, PRL injections given in late hours during the subjective days induce ovarian regression in the photostimulated females. The results suggest that the PRL has an inhibitory role on gonadal photoperiodic responses in redheaded buntings, and extend our understanding of the regulatory function of PRL in migratory birds.

Thyroid and gonad in the oxidative metabolism, erythropoiesis, and light response of the migratory redheaded bunting, Emberiza bruniceps

In the thyroidectomized, adult male redheaded bunting exposed to a L D cycle of 15 09 , there were no significant changes in body weight, gonad size, respiratory rates of whole body, liver, muscle, red blood cell number, hemoglobin concentration, or hematocrit, unlike in intact birds. Further, while testosterone appeared as effective as l-T 4 in determining body weight, gonadal size, and activity and oxygen uptake by skeletal muscle, it was of greater significance for kidney respiration and of secondary importance in its influence on blood morphology and respiratory rates of the liver and of the whole body of the bird.

Photoperiodic control of reproduction in a female migratory bunting (Emberiza bruniceps)

AbstractTwo series of experiments were performed with photosensitive female redheaded buntings. In the first series, birds were exposed to various cycles (8L/16D, 12L/12D, 13L/11D, 15L/9D, and 20L/4D) for 35 days. In the second, birds were maintained for a period of 120 days under long day lengths (15L/9D), short day lengths (8L/16D), and normal day lengths (NDL). Periodic laparotomies of birds under these schedules indicated that long days induced ovarian growth followed by regression and refractoriness, short days were ineffective, and that the birds in NDL showed ovarian growth during periods in the summer of increasing day lengths, followed by spontaneous regression. Groups of photorefractory birds in long days were transferred to short days (8L/16D) for different periods in order to terminate the refractoriness before returning them to 15L:9D for another 20 days. The results from both series of experiments suggest that the female redheaded bunting uses photoperiods as a primary environmental source of information in regulating its reproductive responses. The threshold for its gonadal activities is a photoperiod of 12–13 h daily. A period of insensitivity (photorefractoriness) develops in buntings that are photostimulated, requiring about 8 weeks of short days for its termination.

Photoperiod : Gonadal Growth and Premigratory Fattening in the Redheaded Bunting, Emberiza bruniceps

Photosensitive Redheaded Buntings (Emberiza bruniceps) were exposed to different artificial photoperiods, and continuous light (LL) and darkness (DD) . The daily photoperiods of 12, 13, 15 and 20 hr per day stimulate the gonadal development and the fattening; the rate of growth is however less in the birds exposed to 12 and 13 hr than those exposed to 15 and 20 hr. In contrast, 6L : 18D, 8L : 16D, 10L : 14D and 11L : 13D light regimes fail to stimulate such activities in 4 weeks. In LL, a gonadal-growth-involution cycle is apparent in a duration of 250 days; DD on the other hand, could not stimulate the hypothalamo-hypophysial axis in a 175-day treatment. The results suggest that light is prerequisite for initiation of physiological processes (such as gonadal growth and fattening) in the Redheaded Buntings, and that this species has a definite photoperiodic threshold at between 11 and 12 hr photoperiod to its reproductive and metabolic activities. Further, a period of insensitivity (photorefractoriness) develops in buntings that are stimulated, similar to many north temperate birds.

Photorefractoriness in a Migratory Bunting: A Circadian Mechanism in Its Termination

A circadian rhythm appears to control the termination of the photorefractory period in redheaded buntings. A 6-h photophase coupled with scotophases of varying durations does not terminate the refractory period in the cycles of 12 (6L:6D), 36 (6L:30D), and 60 (6L:54D) h but terminates it in the cycles of 24 (6L:18D), 48 (6L:42D), and 72 (6L:66D) h.

Seasonal variations in extrathyroidal conversion of thyroxine to tri-iodothyronine and migratory disposition in redheaded bunting

Thyroid gland has been shown to be involved in the migratory disposition in redheaded bunting, Emberiza bruniceps, ( Chandola & Pathak, 1980 a,b; Pathak & Chandola, 1982). Extrathyroidal conversion of thyroxine (T4) to triiodothyronine (T3) was now studied in thyroidectomised buntings by measuring the appearance of plasma T3 (RIA) 4h after an injection of 2.5ug I-T4 during non-migratory (January), spring pre-migratory (March) and post-migratory (June) periods of the year. A significantly high peripheral conversion of T4-T3 was recorded during pre-migratory period compared to non-migratory and postmigratory periods. This suggests that the increase in circulating T3 T4 ratio observed in buntings prior to spring migration could be to a certain extent, the result of an enhanced peripheral monodeiodination of T4. The inhibition of extrathyroidal conversion of exogenously administered I-T4 into T3 in thyroidectomised buntings (by propylthiouracil) prevented the T4-induced fattening significantly during non-migratory period (January). Same dose of PTU failed to inhibit T4-induced fattening as well as peripheral monodeiodination of T4 in thyroidectomised birds in spring premigratory period. This indicates that the T4-effects on fattening may be brought about by its conversion to T3, and also that the peripheral deiodinating enzyme systems in this bird may be comparatively more active during spring premigratory period than that during nonmigratory period. The results argue for a role of T3 in premigratory fattening, a characteristic of migratory disposition in birds. Also the seasonal variations in peripheral conversion of T4-T3 may be of great adaptive significance in seasonal breeders where energy requiring events like migratory fattening (and reproduction and molting-all influenced by thyroid status) must be temporally spaced across the year.

The photo-gonadal response of a migratory bunting: evidence of an external coincidence system.

Male redheaded buntings (Emberiza bruniceps) were subjected to continuous darkness (DD) or short days (8L/16D) after photo-stimulation (15L/9D) for either 15 or 30 days. Two groups of birds (four each), after photo stimulation for 30 days, were continued on a regimen of 15L/9D. Another two groups (of four each) of photo-sensitive birds were also subjected to DD or 8L/16D; they served as controls. The effect of transfer to DD or 8L/16D on the size of testes was found not the be dependent upon the size attained at the time of transfer. The rate of testicular regression was nearly the same under both the treatments, i.e., in those birds transferred either to DD or to 8L/16D. The birds that were maintained on 15L/9D maintained enlarged testes; this excluded the possibility of the onset of photo-refractoriness during the treatment period. On the other hand, testes were not photo-stimulated in the photo-sensitive birds subjected to DD or 8L/16D. These results are consistent with the Bünning-Pittendrigh avian external coincidence model, but could be explained alternatively by a relatively simple internal coincidence model. Nevertheless, the application of the law of parsimony suggests the acceptance of the hypothesis of the external coincidence model.

Thyroid, gonad, and photoperiod in the hemopoiesis of the migratory red-headed bunting, Emberiza bruniceps

l-Thyroxine and thyroidectomy, separately or together had no significant influence on the gonadal activity and erythropoiesis of the migratory red-headed bunting maintained under natural photoperiod during January to March. But when exposed to 15L:09D, while there was no significant change in the activity of the testes and erythropoiesis of the thyroidectomized birds, significant increases occurred in those of the intact and l-thyroxine-treated intact and thyroidectomized birds. It is suggested that a long photoperiod acting by way of the thyroid and gonad enhances erythropoiesis which in turn helps the bird in meeting higher oxygen demand during migration and reproduction.

Involvement of thyroid gland in the development of migratory disposition in the redheaded bunting, Emberiza bruniceps

In the redheaded bunting Emberiza bruniceps, thyroidectomy inhibited premigratory fattening and nocturnal restlessness—two characteristics of avian migration—observed in caged birds during the premigratory period (March/April). Thyroxine (T 4) and triiodothyronine (T 3) administration in thyroidectomized birds stimulated locomotor activity and restored the loss in body weight. Annual variations in circulating thyroid hormone concentrations revealed a significant rise in T 3 T 4 ratio prior to spring migration in both years studied. This increase in circulating T 3 T 4 ratio may be associated with the development of migratory disposition in this bird. There was no increase in circulating T 3 T 4 ratio prior to autumnal migration, however, plasma T 4 increased significantly. Different thyroidal mechanisms are most likely involved in spring and fall migratory periods. While T 3 remained low throughout, apart from the characteristic spring rise, high T 4 levels in E. bruniceps were associated with periods of reproduction and molting, the latter coinciding partly with autumnal migration.

Circadian basis of photoperiodically induced testicular growth in redheaded bunting, Emberiza bruniceps

Short day (8L : 16D), pretreated adult male redheaded buntings were held on various light—dark cycles of 20 to 30 h duration, in which a fixed ultra-short photophase of 3 h was combined with scotophases of varying duration. A photoperiodic testicular response was obtained only in 28- and 30-h cycles (3L : 25D and 3L : 27D). The same photo-period (3 h) in 20- to 26-h cycles (3L : 17D, 3L : 19D, 3L : 21D and 3L : 23D) failed to stimulate testicular growth. The results can be interpreted on the assumption that the positive testicular response in this species, under ultra-short-day light cycles, is the result of an advance in the photosensitive phase of the photoperiodic response system so that it coincides at least partly with the external photophase. The results thus appear to conform with the Bünning hypothesis or external coincidence model.