Photoperiodism and the testicular refractory period in the mallard

Abstract

The effects of winter daylengths on the duration of pituitary refractoriness to photostimulation are described. The mallard, as do probably all wild avian species, enters a postnuptial refractory period during which the gonads display no gametogenesis and the anterior pituitary becomes seasonally unresponsive to photostimulation so far as gonadotrophin secretion is concerned. This phase lasts about three months and is an important synchronizer of the breeding cycles. Refractory specimens kept under a summer daylength of 16.5 hours remain unresponsive to photostimulation at a time when birds in their natural environment are emerging from their refractory period. When, however, such birds are subjected to a period of eight hours daylengths there is a shortening of the refractory phase and they display a gonadotrophic response to photostimulation. There is some indication that a phase of winter daylengths is not, however, a necessary pre‐requisite for birds to be capable of emerging from the refractory period and recovering some degree of spermatogenetic activity. Thus, even in some specimens kept under the long photoperiods there were spermatogonia multiplications occurring when the experiment was terminated.

PHOTORESPONSES OF THE WOODPIGEON COLUMBA PALUMBUS IN RELATION TO THE BREEDING SEASON

“…Thus short days in late summer and autumn regulate a reaction in temperate passerine birds that enables a species to respond to subsequent light increases. A similar phenomenon has recently been recorded by Lofts & Coombes (1965) in the Mallard Anas platyrhynchos. In contrast, the refractory period of the xerophilous Weaver Finch Quelea quelea, remains unaffected by such photoperiodic fluctuations .…”

“…Thus, of the five specimens kept on a natural photoperiod, three had produced spermatids, one had secondary spermatocytes, and one was at the all birds studied the breeding season is followed by a period when the pituitary ceases as a response to photo-stimulation to produce, or produces in inadequate quantities or proportions, those hormones necessary for gametogenesis. Furthermore, there is a wealth of experimental evidence to show that in many temperate zone species prolonged or excessive photo-stimulation maintains this refractory condition which can only be ended when the bird is subjected to a fixed schedule of short days (reviews and summaries of this general situaticn are given by Burger 1949, Wolfson 1952, 1959a, Miller 1955, Lofts & Coombes 1965 although this is not necessarily true of some equatorial species (Lofts 1962a). It is also possible with excessive photo-stimulation to accelerate a species like the Red-billed Dioch Quelea quelea through its normal developmental cycle into peak reproductive condition and thence into refractoriness .…”

Gonadal cycles and levels of luteinizing hormone in wild Spur‐winged geese, Plectropterus gambensis

“…As in most species (Lofts & Coombs, 1965;Farner et al, 1983), at the end of the breeding season plasma LH levels fall sharply in male Spur-winged geese and the testes regress (Figs 1 & 7). For most of the population, this occurs in February, although some males remain capable of breeding until early March.…”

EXPERIMENTAL DEMONSTRATION OF A POST‐NUPTIAL REFRACTORY PERIOD IN THE TURTLE DOVE STREPTOPELIA TURTUR

“…He suggested that the physiological preparation for moulting may require more long days than does gonad development and that while short days hasten feather loss and subsequent growth they do so only in birds pre-treated with sufficient long days. In general, experimental exposure to .short days hastens the onset of moult (Miyazaki 1934 , Burger 1941, DamstC 1947), while long days retard the process (Walton 1937, Lofts & Coombes 1965. It is also generally agreed that the thyroid is involved in the moult process (Blivaiss 1947, Assenniacher 1958) while Kobayashi (1957while Kobayashi ( , 1958 has suggested that an inherent cycle of thyrotropin and gonadotropin secretion exists, sufficient.…”