An Investigation of Photo‐refractoriness in the House Sparrow by Artificial Photoperiods

Abstract

Summary The natural testis cycle and associated changes in bill colour of the House Sparrow Passer domesticus are described. Subjects were wild‐caught at three different times in the breeding cycles:in February when the testes were small and contained only spermatogonia, in May when they were fully recrudesced and contained bunches of spermatozoa and in late July at a time when spontaneous gonad regression was occurring as the birds entered their photo‐refractory phase. Each sample was divided into eight separate groups which were given a range of artificial asymmetric skeleton photo‐periods generalized as LD 6 +1/2:131/2; the 1/2‐h light pulse was given at a different point in the dark period in each group. The birds entrained to skeleton schedules simulating complete photoperiods of up to 12 h duration as if the start of the long light pulse was dawn. However, with long‐day simulations (e.g. 6L 111/2 D 1/2 L 6D which simulates an 18 h photoperiod) the birds entrained to the start of the short light pulse to give an effective photoperiod of 121/2 h (that is, 1/2L 6D 6L 111/2D). The skeleton schedules simulating 14 h and 16 h were interpreted as such in February and were not effective in causing testicular induction, but they were apparently read as days of 161/2 h and 141/2 h in May, and as such maintained active spermatogenesis. The differences are discussed in terms of the changed frequency of a circadian oscillator. When birds captured in July were held on the various skeleton light schedules refractoriness was ended for most the subjects, as was proved by subsequently exposing them to a complete 16‐h photoperiod. Exceptions were the birds in the group given the 14‐h simulation, for these entrained as they had in May and so were effectively receiving a long 161/2‐h day. The discussion presents evidence to show that photoperiods in excess of 14 h cause the light sensitive phase of a circadian oscillator responsible for luteinizing hormone secretion to be phased into the non‐inductive period of darkness. Rehabilitation of the interstitial components of the testis is apparently inhibited in such circumstances.

Control of annual reproductive cycle in the subtropical house sparrow (Passer domesticus): evidence for conservation of photoperiodic control mechanisms in birds

“…This is interesting since a previous study on Indian house sparrows at 22°N, 88°E reported a longer breeding season lasting for 10 months [ 39 ]. The difference in reproductive cycle of these two Indian studies could be attributed to the difference in the food availability as a consequence of the differences in changes in temperature over seasons at these two latitudes, similar to that reported for high latitude birds [ 34 , 35 , 40 , 41 ]. In Threadgold's study also, sparrows of 34°N had longer breeding season than those of 52°N [ 36 ].…”

“…Further, there could be differences in the breeding seasons among house sparrow populations from relatively similar latitudes. Murton and Westwood [ 34 ] in their study on British sparrows found Surrey (51°N) sparrows in more advanced stage of their vernal recrudescence than Cambridgeshire (52°N) sparrows at the same time of the year. The difference in the timing of breeding of sparrows was probably due to the differences in food availability as a consequence of ambient temperatures at two places, and not due to photoperiodic conditions which were almost the same.…”

Photoperiodic control of testicular regression and moult in male House Sparrows Passer domesticus

“…gonadal regression does not occur until after the solstice. as daylength is decreasing (Murton & Westwood 1974). Yet House Sparrows are known to become absolutely refractory: exposure to long days after gonadal regression fails to induce gonadal recrudescence (Riley 1936) and exposure to short days is required to restore photosensitivity (Vaugien 1955).…”

Photoperiodic control of budgerigar reproduction: circadian changes in sensitivity

“…In view of this possibility, we cannot be absolutely certain where, within the period 12-18 h after dawn, the peak of sensitivity lies. Against this possible interpretation must be held Menaker's (1965) finding that phase jumping and entrainment of the activity rhythm to the start of the shorter of the two light pulses occurs only with skeleton schedules simulating photoperiods of about 14 h total duration or more (see also Murton & Westwood, 1974). Thus the evidence in these experiments that the period of peak sensitivity lies between 12-16 h after dawn is subs tanti al.…”