Don\u27t put all your eggs in one basket: the effects of brood size manipulation on oxidative stress, telomere length, and juvenile survival in the Savannah sparrow (Passerculus sandwichensis)

The disposable soma hypothesis proposes that short-lived organisms should sacrifice long-term survival in favor of short-term survival or reproductive success as they allocate limited resources to competing energetic demands. For birds in a nest, investment in growth to reach adult size helps ensure short term survival, while investment in self-maintenance preserves tissues for future survival. Conditions early in life can alter these physiological tradeoffs and may create substantial and lasting effects in animals. Oxidative stress, which is produced by cellular respiration and causes damage to cells, is one currency that may respond to environmental conditions to mediate these tradeoffs. We manipulated broods of Savannah sparrows (Passerculus sandwichensis) nesting on Kent Island, New Brunswick, Canada, to alter resource availability for nestlings. Compared with control and enlarged broods, reduced broods gained more mass, resulting in greater survival to independence, and also demonstrated lower levels of lipid peroxidation and fewer critically short telomeres. In enlarged broods, nestlings sacrificed self-maintenance in favor of growth; their shorter telomeres and higher levels of lipid peroxidation suggest they may experience more rapid ageing and a shorter lifespan. Thus, these findings offer support for the predictions of the disposable soma hypothesis, since nestlings facing limited resources attempted to improve short-term survival by gaining mass at the expense of future survival. Furthermore, after fledging, levels of lipid peroxidation were reduced but telomere lengths remained unchanged, suggesting that a short period of high stress early in life can inflict both short- and longterm physiological consequences