Parent age, lifespan and offspring survival: structured variation in life history in a wild population

Abstract

Summary 1.Understanding the degree to which reproductive success varies with an individual's age and lifespan, and the degree to which population-level variation mirrors individual-level variation, is central to understanding life-history evolution and the dynamics of age-structured populations. We quantified variation in the survival probability of offspring, one key component of reproductive success and fitness, in relation to parent age and lifespan in a wild population of red-billed choughs (Pyrrhocorax pyrrhocorax). 2. On average across the study population, the first-year survival probability of offspring decreased with increasing parent age and lifespan; offspring of old parents were less likely to survive than offspring of young parents, and offspring of long-lived parents were less likely to survive than offspring of short-lived parents. 3. However, survival did not vary with parent age across offspring produced by groups of parents that ultimately had similar lifespans. 4. Rather, across offspring produced by young parents, offspring survival decreased with increasing parent lifespan; parents that ultimately had long lifespans produced offspring that survived poorly, even when these parents were breeding at young ages. 5. The average decrease in offspring survival with increasing parent age observed across the population therefore reflected the gradual disappearance of short-lived parents that produced offspring that survived well, not age-specific variation in offspring survival within individual parents. 6. The negative correlation between offspring survival and maternal lifespan was strongest when environmental conditions meant that offspring survival was low across the population. 7. These data suggest an environment-dependent trade-off between parent and offspring survival, show consistent individual variation in the resolution of this trade-off that is set early in a parent's life, and demonstrate that such structured life-history variation can generate spurious evidence of senescence in key fitness components when measured across a population.

Invader population speeds up life history during colonization

“…predator susceptibility or competition for resources that reduces the survival probability of the offspring of young reproducers (e.g., Reid et al 2010). Hence, if age at first-time reproduction (i.e., 1-vs. 2-year old fish) has a genetic component in vendace, the r-selected, early maturation strategy is likely to become the dominant trait in the colonist population, just as observed in the present study.…”

Causes and consequences of individual variability and specialization in foraging and migration strategies of seabirds

“…Young breeders may be less successful at foraging because they are poorer at locating prey, physically less capable (Curio 1983) or because they are showing restraint because of their higher residual reproductive value (Williams 1966). A further challenge is to establish whether individuals improve their foraging performance with age, and if the higher average performance of older age classes is due to differential survival rates of individuals of differing foraging abilities (Smith 1981, Nol & Smith 1987, Reid et al 2010. Longitudinal studies are therefore essential to establish the relative importance of within-individual improvements and natural selection (Limmer & Becker 2009).…”

Nestling erythrocyte resistance to oxidative stress predicts fledging success but not local recruitment in a wild bird

“…This was empirically demonstrated by manipulations of sibling competition or growth rate, which translated into increased oxidative damage [10], reduced antioxidant levels [11] or reduced erythrocyte resistance to oxidative stress [12], although some studies failed to detect such effects [13,14]. For these reasons, and because oxidative stress has been reported to predict life expectancy in some studies of birds [15,16], one might expect individual resistance to oxidative stress at an early age to explain variance in offspring fledging success and recruitment probability, both major correlates of offspring survival [17]. A link between pre-fledging oxidative damage and recruitment probability was reported in the long-lived European shag Phalacrocorax aristotelis and provides the first piece of evidence of a long-lasting effect of oxidative processes [18].…”