Avian senescence: underlying mechanisms

Abstract

Candidate mechanisms for physiological aging include free radical production and resulting oxidative damage, progressive erosion of telomeres and cellular senescence, age-dependent trade-offs in hormone signaling pathways, and immunosenescence, leading to an increased risk of infection, autoimmune disease, and cancer. These mechanisms are inter-related, not mutually exclusive, and probably all contribute to the aging phenotype. To date, most studies on mechanisms of aging are based on cell culture or lab animals, but interest in comparative studies is growing rapidly. Compared to mammals, birds have long life spans for their body sizes. Birds also appear to have lower rates of free radical production and oxidative damage than mammals, despite higher levels of oxidative metabolism. High levels of the antioxidant, uric acid, in birds may help protect against oxidative damage. Cultured bird cells are more resistant to oxidative damage than mammal cells, and membrane phospholipids of birds are less susceptible to peroxidation than those of mammals of the same size, but show a similar susceptibility as those of mammals with the same life span. In birds, telomeres shorten with age, and the rate of shortening is proportional to life span. Telomerase has a higher activity in long-lived than in short-lived species. Within a species, short telomeres correlate with reduced survival. Birds have higher plasma glucose than mammals, but lower levels of protein glycation, which contributes to aging damage. Immunosenescence is linked to both oxidative damage and telomere shortening. Patterns of cellular and humoral immunosenescence differ among species in birds. The rate of decline in cell-mediated immune function is inversely correlated with life span. Comparative studies on mechanisms underlying senescence in birds will continue to provide us with valuable information on how aging mechanisms have evolved.

Either taking it easy or feeling too tired: old Cory’s Shearwaters display reduced activity levels while at sea

“…The decline in the PHA response by aged Cory's Shearwaters is consistent with results from recent studies indicating that immunosenescence may be common in both short and long-lived bird species (Haussmann et al 2005;Vleck et al 2007). It also suggests that Old birds in our study had reached an age where senescence effects might be apparent (see also Mougin 2002).…”

“…Therefore, measuring other aspects of individual state and performance may contribute to a better understanding of the mechanisms of aging, and hence of the biology of senescence. Although there has been recent research focusing on hormonal, physiological and cellular parameters (Haussmann et al 2005;Vleck et al 2007), surprisingly few studies have explored the effects of aging of wild animals on traits such as foraging behaviour and efficiency (but see Catry et al 2006;MacNulty et al 2009;Lecomte et al 2010). Such traits are highly relevant because they influence the rate of resource acquisition, and hence have major implications for fitness correlates that include reproductive output and survival.…”

Age and Breeding Effort as Sources of Individual Variability in Oxidative Stress Markers in a Bird Species

“…Studies describing changes in oxidative stress throughout life are abundant in mammalian literature (Oztürk and Gümüşlü 2004;Gil et al 2006). In contrast, avian reports are mostly limited to the early stages of life because data on aged birds are scarce (e.g., Alonso-Alvarez et al 2006;Torres and Velando 2007;Vleck et al 2007). Furthermore, as far as we know, no avian study describes the change in any marker of oxidative damage across the full age range (i.e., from youth to old age; see also the review by Vleck et al [2007]).…”

Frailty in state-space models: application to actuarial senescence in the Dipper

“…Birds constitute an attractive group of organisms for comparative studies of senescence, first because they are relatively long-lived for their body sizes compared to mammals due to their slower life histories (Jones et al 2008), and second because data on wild birds have been collected in a wide range of avian species (Vleck et al 2007). Several studies of short-lived birds have recently shown evidence for survival senescence (e.g., Fox et al 2006, Keller et al 2008.…”