J.P. Thapliyal

Thyroid in avian reproduction

Annual gonadal size and activity cycles of the nonmigratory Indian finches, viz: Lal Munia (Estrilda amandava) and Spotted Munia (Uroloncha punctulata), run parallel with the body weight cycles and are inversely related with the thyroid activity cycles. Gonads are developed when thyroid activity is low and are reduced when it is high. n nFurther, severe hypothyroidism (thyroidectomy) induces gonadal recrudescence to full development, which is then maintained; and hyperthyroidism (l-thyroxine) at low levels reduces the weight, and at moderately high levels the activity also, of the gonads of adult normal and thyroidectomized birds during the breeding phase. n nIt is suggested that changes in thyroid activity influence the output of the gonad-stimulating hormones from the adenohypophysis, which in turn regulate the annual and body weight cycles of Lal and Spotted Munia.

Scoto/photo‐periodic responses of a sub‐tropical finch (Spotted munia) in relation to seasonal breeding cycle

Abstract Effects of continuous light and dark periods and long and ultrashort photoperiods on the gonadal function of a subtropical finch, Spotted munia, hitherto considered “non‐photosensitive”, were studied. This bird seems to be unique in that while gametogenesis and hormone production are stimulated by the continuous or long scoto periods the endogenous rhythm of reproduction continues in constant 24hr or 15hr long daily photoperiod.

Effect of pinealectomy on the annual testicular cycle of Calotes versicolor

Abstract Pinealectomy resulted in an earlier recrudescence and a later regression of the annual gonadal cycle of the lizard Calotes versicolor . Spermatozoa appeared early and were present throughout the course of the experiment, namely, for 11 months. In control lizards (sham-operated, intact), on the other hand, spermatozoa appeared in late April and were observed only until August, a period of 5 months. The sex segments of the kidneys showed a cycle similar to the cycle of the testes in both groups.

Thyroidectomy and gonadal development in common myna, Acridotheres tristis

Abstract Thyroidectomy inhibited the gonadal development in the common myna, during quiescent, progressive, and reproductive phases. But, when performed during late reproductive and regressive phases it had no effect on the annual gonadal cycle.

Role of thyroid and testicular hormones in the oxidative metabolism of the Indian garden lizard, Calotes versicolor

L-Thyroxine (L-T4) and testosterone were administered separately to intact, thyroidectomized, and castrated male Indian garden lizards, Calotes versicolor (maintained under natural climatic conditions) throughout the year to study their effects on the whole-body oxygen consumption and on tissue (liver, muscle, kidney, and brain) respiration. The findings indicate that the calorigenic actions of L-T4 and testosterone are independent of ambient temperature, and different tissues have different, temperature-independent, annual rhythms of sensitivity to L-T4 and testosterone. Internal factors seem to play a major role in the determination of these annual tissue sensitivity rhythms. Effects of thyroidectomy and castration are brought about by decreased levels of both thyroidal and testicular hormones. It is suggested that gonadal hormones are directly involved in the oxidative metabolism of Calotes which is regulated jointly by thyroid and gonadal steroids, and the degree of involvement of the glands depends upon the energy demand and sensitivity of tissues during different months of the year.

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-T4 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.

Effect of pinealectomy on the photoperiodic gonadal response of the Indian garden lizard, Calotes versicolor

Abstract Pinealectomy during early summer partially, but significantly, inhibits the decrease in the gonad size of lizards subjected to short photoperiods. During early winter, it significantly accelerates the growth of the testes in animals subjected to constant long photoperiods. It is proposed that the pineal, as in mammals and some birds, probably acts by way of the neuroendocrine complex.

Endocrine Regulation of Body Weight in the Spotted Munia, Uroloncha punctulata

Literature on the body-weight cycles of nonmigratory birds is meager (Nice 1937, 1938, 1946; Baldwin and Kendeigh 1938), and consequently the factors that regulate these cycles are only incompletely understood (Farner 1955). The mean body weight of a bird that has free access to food, it has been suggested, may change because of alteration in the level of the activity of the hypophysis (Wolfson 1952; Farner 1960; King and Farner 1963; Meier and Farner 1964) or of the gonads (Hbhn 1947; see also review by Farner 1955), or even of the thyroid (Schildmacher and Rautenberg 1952). However, experimental investigations of the body-weight cycles have been confined mostly to migratory birds. Recently Thapliyal (1966) and Thapliyal and Pandha (1966) have shown in the nonmigratory Spotted Munia, Uroloncha punctulata, that during the breeding phase the average weight of males is significantly higher than that of females (fig. 1). It has also been reported (Thapliyal 1966) that, while orchiectomy had no influence, thyroidectomy induced a rapid increase in the body weight of the birds, and after some time the mean body weights of the two sexes overlapped. To explain, it was suggested that the mechanisms that control the body weight of a Spotted

Thyroid and annual gonad development, body weight, plumage pigmentation, and bill color cycles of lal munia, Estrilda amandava.

Long-term administration of L-thyroxine (T4) in the wax bill (lal munia) inhibited the current gonad development cycle, and the increase in gonadal volume in the second cycle was suppressed only by higher concentrations. Gonadal inhibition by high but not by low doses of L-T4 was associated with a failure in the development of LH-dependent pigmented nuptial plumage. This suggests that L-T4 depresses FSH secretion more readily than LH secretion. The results indicate that the effects of L-T4 administration on the body weight cycle depends upon the physiological and/or gonadal status of the bird at the start of the experiment and that the juvenile hypothalamo-hypophysial-gonadal axis is more sensitive to L-T4 than that of the adult birds. The bill color, like plumage pigmentation, appears to be LH controlled. It is suggested that while thyroid hormone, acting by way of the hypothalamo-hypophysial complex and/or by direct action on the feather papillae, modulates the annual cycles of plumage pigmentation, bill color, gonad development, and body weight of lal munia, the finch has an endogenous mechanism which enables it to adapt to chronic hyperthyroidism in such a way that breeding occurs at the normal time of the year.

The thyroid and the hypophysial gonadal axis in the female Spotted Munia, Uroloncha punctulata

Abstract When adult female Spotted Munia (Uroloncha punctulata) are surgically thyroidectomized the diameter of the ovarian follicles and the weight of the body start incrasing, reach a maximum, and then hold a plateau. In the juveniles, while there is an early, though partial, but significant increase in the weight of the body and of the ovary, maximal development occurs only at the approach of the breeding season. Further, although the dark pigment and its deposition pattern on the feathers remain unaffected, in the absence of the thyroids feather growth is retarded and the development of the barbules is inhibited. It is suggested that the effects on the plumage are probably due to an indirect action of the thyroids by way of the body metabolism, but that those on the body weight and ovary are due to the direct influence on the hypothalamo/hypophysial/gonadal axis.