Reproductive improvement and senescence in a long-lived bird

Abstract

Heterogeneity within a population is a pervasive challenge for studies of individual life-histories. Population-level patterns in agespecific reproductive success can be broken down into relative contributions from selective disappearance, selective appearance of individuals into the study population, and average change in performance for survivors (average ontogenetic development). In this article, we provide an exact decomposition. We apply our formula to data on the reproductive performance of a well characterized population of common terns (Sterna hirundo). We show that improvements with age over most of adult life and senescence at old ages are primarily due to a genuine change in the mean among surviving individuals rather than selective disappearance or selective appearance of individuals. Average ontogenetic development accounts for approximately 87% of the overall age-specific population change.common tern (Sterna hirundo) | age-specific reproduction | aging | heterogeneity | exact decomposition approach I n the study of life-histories it is important to capture the performance of individuals and changes in that performance over age. Changes in performance are often reported as changes in population averages, but individual heterogeneity can produce dynamics at the observed population level that are very different from dynamics at the individual level (1-3)."Population level" refers to the observed averaged information over all individuals present at a given age regardless of whether they survive to the next age step. What we define as population change is the change observed directly in the aggregate field data and not the change in a hypothetical population of all individuals that were present at a given starting age x. "Individual level" refers to the change over age for each surviving individual averaged over all these survivors. We call this term "average ontogenetic development."The interpretation of population-level patterns can be problematic because of "within-generation phenotypic selection" (4). This is a change in the composition of the population if selective mortality removes frail (of lower quality) individuals at an earlier age than those individuals that are less frail (of higher quality) (1, 2), or if individuals that enter the population (here breeding population) as adults later than others through delayed recruitment or immigration (5) have a different performance than the resident population. We use the phrase "selective disappearance" to denote change in the mean of a phenotypic trait due to mortality and "selective appearance" to denote change due to new appearance of individuals. The term "compositional change" is used to refer to the combination of both selective appearance and disappearance. We develop a method to exactly decompose population change in an age-specific phenotypic trait with repeated measures into the components: average ontogenetic development, selective disappearance, and selective appearance.An Approach to Decomposing Population Change. If there is no selecti...

Telomere length reflects phenotypic quality and costs of reproduction in a long-lived seabird

“…This could be owing to a superior body condition [34] and/or a higher efficiency in behavioural traits related to chick rearing, because a higher reproductive output does not necessarily imply an elevated parental effort [62]. This is in line with the finding that in our population the individuals with high reproductive success also have a relatively long average lifespan [61,63], but the extent to which telomere dynamics affect lifespan in common terns remains to be established.…”

Life-History Differences in Age-Dependent Expressions of Multiple Ornaments and Behaviors in a Lekking Bird

“…The application of mixed models to longitudinal data has bypassed this major limitation and revealed that within-and between-individual effects can differ in many situations and that both can result in a positive association between age and trait expression at the population level (van de Pol and Verhulst 2006;van de Pol and Wright 2009;Rebke et al 2010). Most longitudinal studies published to date have analyzed key life-history traits, such as reproductive success (e.g., Dugdale et al 2011;Froy et al 2013) and survival (e.g., Bouwhuis et al 2012), but there is growing interest in age-dependent variation in secondary sexual traits (Balbontín et al 2011;Evans et al 2011) and behavior (Mainguy and Côté 2008;Nussey et al 2009).…”

The Quest for Immortality in Triatomines: A Meta-Analysis of the Senescence Process in Hemimetabolous Hematophagous Insects

“…In the field, triatomines could die before intrinsic mortality and decreasing fecundity occurs, due to extrinsic factors such as predation, parasitism, extreme climatic conditions, etc. Recent studies in vertebrates (Adams, 1985;Gaillard et al, 1993;Reznick et al, 2002;Rebke et al, 2010) show that senescence is observed under natural conditions, but that kind of information is lacking for triatomines and needs to be investigated. Williams (1957) claimed that greater rates of extrinsic mortality (age-and condition-independent) favored more rapid senescence, but Abrams (1991) showed that the effects of the "extrinsic" mortality affect differentially the rate of senescence as a function of the degree of densitydependence.…”