New Perspectives on Avian Models for Studies of Basic Aging Processes.

Avian models have the potential to elucidate basic cellular and molecular mechanisms underlying the slow aging rates and exceptional longevity typical of this group of vertebrates. To date, most studies of avian aging have focused on relatively few of the phenomena now thought to be intrinsic to the aging process, but primarily on responses to oxidative stress and telomere dynamics. But a variety of whole-animal and cell-based approaches to avian aging and stress resistance have been developed-especially the use of primary cell lines and isolated erythrocytes-which permit other processes to be investigated. In this review, we highlight newer studies using these approaches. We also discuss recent research on age-related changes in neural function in birds in the context of sensory changes relevant to homing and navigation, as well as the maintenance of song. More recently, with the advent of "-omic" methodologies, including whole-genome studies, new approaches have gained momentum for investigating the mechanistic basis of aging in birds. Overall, current research suggests that birds exhibit an enhanced resistance to the detrimental effects of oxidative damage and maintain higher than expected levels of cellular function as they age. There is also evidence that genetic signatures associated with cellular defenses, as well as metabolic and immune function, are enhanced in birds but data are still lacking relative to that available from more conventional model organisms. We are optimistic that continued development of avian models in geroscience, especially under controlled laboratory conditions, will provide novel insights into the exceptional longevity of this animal taxon.

Ovarian aging in developmental and evolutionary contexts.

Evolutionary theory predicts that aging-related fertility declines result from tradeoffs between reproduction and somatic maintenance. Developmental programs for oogenesis also contribute to variation in aging-related reproductive declines among female vertebrates. Documented reproductive aging patterns in female vertebrates, including humans, are consistent with canonical aging patterns determined developmentally and require no special adaptive explanation. Here we discuss patterns of aging-related ovarian decline in diverse female vertebrates, and place human ovarian aging in comparative context. Depletion of finite oocyte stores accompanied by fertility loss occurs in a variety of nonhuman mammals and vertebrates, including short-lived rodents, birds, and some fishes; moreover, postreproductive lifespans of considerable length clearly are not limited to long-lived, social species with well-developed kin networks. We argue for a more rigorous comparative approach for understanding the evolutionary and developmental bases of ovarian aging in vertebrates with a wider range of aging patterns and social structures.

Naturally long-lived animal models for the study of slow aging and longevity.

Judicious selection of new animal models for the study of basic aging processes must combine feasibility and good use of the comparative method with evidence of antiaging adaptations, like the ability to combat oxidative damage to cells and tissues. A number of vertebrate species already in use or being developed as new biomedical models lend themselves very well to laboratory studies of aging, including small birds, bats, and mole-rats.

Reproductive aging in female birds.

Birds are underutilized as animal models for studying the basis of longevity, cellular adaptations for resisting oxidative damage, and delayed reproductive senescence. Reproductive aging patterns in female birds range from slightly slower than those in rodents of similar size to extremely slow or even negligible. The best-studied laboratory bird model of female reproductive aging is the relatively short-lived, rapidly aging domestic laying hen. Promising long-lived avian models for the prolongation of fertility include cage birds, like the budgerigar, and wild seabirds, like the Common Tern, many of which show no reproductive aging in nature. Preliminary comparisons of ovarian aging patterns in Japanese quail and budgerigars suggest that declining stores of primary oocytes may play different roles in fertility declines in these two species, as they do among mammals.

Is postmenopausal life-span a gift of modern health or a product of natural selection?

The author discusses how researchers from various scientific disciplines view the origins of and mechanisms (evolutionary as well as physiological) underlying menopause in humans. She describes presentations from a symposium centered around interdisciplinary perspectives on female reproductive aging. Comparative zoology, primatology, and anthropology have much to contribute to our understanding of human menopause; hence the symposium contained speakers representing these subdisciplines, as well as the more typical disciplines of endocrinology and neurobiology.