Great tits growing old: selective disappearance and the partitioning of senescence to stages within the breeding cycle

Abstract

Deterioration of reproductive traits with age is observed in an increasing number of species. Although such deterioration is often attributed to reproductive senescence, a within-individual decline in reproductive success with age, few studies on wild animals have focused on direct fitness measures while accounting for selective disappearance and terminal effects, and to our knowledge none have determined how senescence effects arise from underlying reproductive traits. We show for female great tits that such an approach helps understanding of the onset, impact and architecture of senescence. Cross-sectional analysis of 49 years of breeding data shows annual recruit production to decline from 3.5 years of age, this decline affecting 9 per cent of females each year. Longitudinal analyses, however, show that selective disappearance of poor-quality breeders partly masks senescence, which in fact starts at 2.8 years and affects 21 per cent of females each year. There is no evidence for abrupt terminal effects. Analyses of underlying traits show no deterioration in clutch size, but significant declines in brood size and fledgling number. Furthermore, these traits contribute K9, 12 and 39 per cent to the senescent decline in recruit production, respectively. Besides providing detailed knowledge of the patterns and architecture of senescence in a natural population, these results illustrate the importance of modelling individual variation, and facilitate study of the underlying mechanisms of senescence.

Why marathon migrants get away with high metabolic ceilings: towards an ecology of physiological restraint

“…During such endeavours it remains important to pay attention to constraints other than work level, especially time limitations, that may prevent animals from eating for long enough to keep up with the high energy expenditure (Tinbergen and Verhulst, 2000;Kvist and Lindström, 2000). When interpretable aspects of the ecological context can be linked to maximal performance, or rather to the relationships between experimentally manipulated work levels and both reproduction and survival (Fig.4) [see Bouwhuis et al for a possible field setting (Bouwhuis et al, 2009)], we may achieve deeper levels of understanding of the selection factors driving the height of metabolic ceilings.…”

Senescence or selective disappearance? Age trajectories of body mass in wild and captive populations of a small-bodied primate

“…To assess how declining individual performance versus earlier mortality of low-quality individuals shape demographic processes and hence selection pressures, it is necessary to simultaneously estimate functional declines and selective disappearance in a population. So far, few studies have taken this approach [10,12,13], and thus the relative importance of these processes within populations and across taxa is largely unresolved.…”

“…The increase in mortality probably results from functional senescence (FS, within-individual deterioration of physical or physiological functioning with advancing age), which, along with terminal disease or investment in reproduction at the expense of maintenance [5][6][7][8], can expose individuals to extrinsic hazards in a condition-dependent manner. Therefore, only high-quality individuals may survive to an age where FS takes effect, making ageing difficult to observe in cross-sectional studies of natural populations [9][10][11][12][13].…”

Relatedness and age reduce aggressive male interactions over mating in domestic fowl

“…This is because as individuals senesce they undergo a decline in residual reproductive value (Fisher 1930) which reduces their reproductive success (Bouwhuis et al 2009;Reed et al 2008). Older males, with reduced ejaculate competitive ability (Jones & Elgar 2004;Dean et al 2010), may therefore increase their overall aggressive interactions towards competitors to prevent sperm competition and protect their paternity.…”

“…While it is well established that age can affect direct fitness (Reed et al 2008;Bouwhuis et al 2009), researchers have also suggested implications for inclusive fitness (Libertini 1988;Lee 2003;Bourke 2007;Ronce et al 2010). …”