Food deprivation during photosensitive and photorefractory life-history stages affects the reproductive cycle in the migratory Red-headed Bunting(Emberiza bruniceps)

Abstract

SUMMARY In a seasonally breeding bird species, food deprivation affects reproduction. A key question is whether food shortage at any time in the year will affect reproduction even though the food supply subsequently becomes adequate. A prediction would be that a food supply that is of shorter duration than that optimally required during a life-history stage will have consequential effects on the succeeding life-history stages. Two experiments investigated this in gonadally regressed migratory Red-headed Buntings(Emberiza bruniceps) at two life-history stages: photosensitive and photorefractory. Experiment 1 employed two groups of photosensitive birds, and experiment 2 employed two groups of photorefractory birds. In both the experiments, birds were exposed for 8 weeks to a neutral day length at dim light intensity (12 h light: 12 h darkness, 12L:12D; L=∼5 lux, D=0 lux)with restricted feeding regimes (6 h food present: 18 h food absent, P:A 6:18 or P:A 12:12) and subsequently maintained for another 13 weeks at a highly stimulatory day length (16L:8D; L=400 lux; D=0 lux) with food ad libitum. We report that the pretreatment with restricted food cycles influenced the subsequent photoperiodic induction of reproductive (testis growth and molt) but not of metabolic (body fattening and mass gain)functions. The testicular response cycle under 16L:8D had a significantly lower amplitude in birds pretreated with P:A 6:18 than with P:A 12:12. Similarly, the recovery of photosensitivity was slower in photorefractory birds pretreated with P:A 6:18 than with P:A 12:12 food cycles. Overall, our findings show for the first time in a seasonally breeding vertebrate species that food deprivation during non-breeding periods of the annual cycle can affect reproductive functions later in the year.

Circadian rhythms are not involved in the regulation of circannual reproductive cycles in a sub-tropical bird, the spotted munia

“…However, a link between the circadian and circannual rhythms is not ruled out at present as the circannual system may influence circadian rhythms (Ball and Ketterson, 2008;Mrosovsky et al, 1976). Although food availability can influence gonadal growth in seasonally breeding songbirds (Kumar et al, 2001;Budki et al, 2009), we would like to speculate based on the present results that energy turnover, enforced by the seasonality in the abundance of food resources, is not controlling the circannual rhythm underlying seasonal reproduction in the spotted munia.…”

Persistence of circannual rhythms under constant periodic and aperiodic light conditions: sex differences and relationship with the external environment

“…They accurately anticipate a favorable season and physiologically prepare themselves well in advance, as mistiming will have severe fitness consequences (Helm et al, 2009). Annual life-history stages begin and end at optimal times, and do not last shorter or longer than the optimal durations (Gwinner, 1996a;Gwinner, 1996b;Dawson, 2008;Budki et al, 2009).…”

Temperature alters the photoperiodically controlled phenologies linked with migration and reproduction in a night-migratory songbird

“…Also, temperature influences the food availability, which has significant effects on the photoperiodic induction of the daily and seasonal responses [26]. Budki et al [27] have reported that food deprivation during the non-breeding periods of the annual cycle affects the reproductive functions later in the year in the migratory redheaded buntings (Emberiza bruniceps). This implies that cues to which a species is exposed during a life-history stage possibly affect the events during the subsequent life-history stage [27].…”