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

Abstract

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 Bunting (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= approximately 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.