Life‐history theory concerns the trade‐offs that mold the patterns of investment by animals between reproduction, growth, and survival. It is widely recognized that physiology plays a role in the mediation of life‐history trade‐offs, but the details remain obscure. As life‐history theory concerns aspects of investment in the soma that influence survival, understanding the physiological basis of life histories is related, but not identical, to understanding the process of aging. One idea from the field of aging that has gained considerable traction in the area of life histories is that life‐history trade‐offs may be mediated by free radical production and oxidative stress. We outline here developments in this field and summarize a number of important unresolved issues that may guide future research efforts. The issues are as follows. First, different tissues and macromolecular targets of oxidative stress respond differently during reproduction. The functional significance of these changes, however, remains uncertain. Consequently there is a need for studies that link oxidative stress measurements to functional outcomes, such as survival. Second, measurements of oxidative stress are often highly invasive or terminal. Terminal studies of oxidative stress in wild animals, where detailed life‐history information is available, cannot generally be performed without compromising the aims of the studies that generated the life‐history data. There is a need therefore for novel non‐invasive measurements of multi‐tissue oxidative stress. Third, laboratory studies provide unrivaled opportunities for experimental manipulation but may fail to expose the physiology underpinning life‐history effects, because of the benign laboratory environment. Fourth, the idea that oxidative stress might underlie life‐history trade‐offs does not make specific enough predictions that are amenable to testing. Moreover, there is a paucity of good alternative theoretical models on which contrasting predictions might be based. Fifth, there is an enormous diversity of life‐history variation to test the idea that oxidative stress may be a key mediator. So far we have only scratched the surface. Broadening the scope may reveal new strategies linked to the processes of oxidative damage and repair. Finally, understanding the trade‐offs in life histories and understanding the process of aging are related but not identical questions. Scientists inhabiting these two spheres of activity seldom collide, yet they have much to learn from each other.

Long chain polyunsaturated fatty acids (PUFAs) are critical structural components of the brain and essential for normal brain development. The cellular transportation and physiological actions of PUFAs are mediated by fatty acid binding proteins (FABPs) which are encoded by the intracellular lipid-binding protein gene family. Three of the ten mammalian FABPs identified to date (FABP3, FABP5, FABP7) are expressed in the brain. These three FABPs, along with their fatty acid ligands, have distinct and dynamic spatio-temporal expression profiles that correlate with specific developmental stages and processes in the brain. Functional studies have revealed a variety of roles for FABPs in brain development including the generation of neuronal and/or glial cells, differentiation, neuronal cell migration and axis patterning. A number of transcription factors have been shown to be involved in the developmental regulation of FABP gene expression in the brain. Furthermore, FABPs appear to be major downstream effectors of signaling pathways such as Reelin-Dab1/Notch which mediate neuron-glia crosstalk during brain development. As PUFAs and FABPs play critical roles in brain development, considerable effort has been placed in elucidating their function in the pathogenesis and progression of brain cancers and neuropsychiatric disorders.

Summary1. Life-history theory predicts that high reproductive investment alters self-maintenance. Several mechanisms underlying the cost of reproduction have been previously suggested, but how parental effort may impact cell and organism maintenance remains largely unknown. The effects of oxidative stress -the imbalance between oxidative damage and defences -on telomere dynamics may underlie this relationship. Indeed, oxidative stress is associated with costly activities like breeding, and impacts telomere length that is known to predict survival in birds. According to life-history theory, long-lived species are expected to minimize the adverse effects of current reproduction on their body maintenance and should therefore enhance their antioxidant capacity and preserve their telomeres when breeding workload increases. 2. In this study, we tested this hypothesis by determining experimentally how the oxidative status and telomere length were modified when long-lived Ade´lie penguins (Pygoscelis adeliae) faced a costly reproductive event. The breeding workload was increased through a handicapping procedure that increased the cost of foraging and therefore chick-provisioning. 3. In agreement with our hypothesis, Ade´lie penguins substantially increased their antioxidant defences during a costly breeding effort, while oxidative damage and telomere length remained unchanged. 4. As expected in long-lived species, Ade´lie penguins subjected to increased breeding constraints appear to prioritize self-maintenance as shown by their increased antioxidant capacity. Moreover, the absence of effects of our experimental procedure on telomere length suggests no apparent impact of breeding workload on the senescence of this long-lived bird. However, to better understand the role of the couple 'oxidative status ⁄ telomeres' in the regulation of life-history strategies, further studies should examine: (i) the nature and the cost of additional antioxidant protection; (ii) the changes in the oxidative status of animals throughout their annual cycle and the consequences on telomere dynamics; and (iii) the repartition of antioxidant resources between young and parents.

The use of oxidative status markers in animal conservation is dual-faceted, as they reflect the effects of environmentally-induced stress on animal populations and they predict individuals' fitness prospects. Paradoxically, conservation studies rarely include them. Here, we raise awareness of their use, and show how they can valuably complement conservation studies.

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