Evidence for senescence in survival but not in reproduction in a short-lived passerine

Abstract

Senescence has been studied since a long time by theoreticians in ecology and evolution, but empirical support in natural population has only recently been accumulating. One of the current challenges is the investigation of senescence of multiple fitness components and the study of differences between sexes. Until now, studies have been more frequently conducted on females than on males and rather in long-lived than in short-lived species. To reach a more fundamental understanding of the evolution of senescence, it is critical to investigate age-specific survival and reproduction performance in both sexes and in a large range of species with contrasting life histories. In this study, we present results on patterns of age-specific and sex-specific variation in survival and reproduction in the whinchat Saxicola rubetra, a short-lived passerine. We compiled individual-based long-term datasets from seven populations that were jointly analyzed within a Bayesian modeling framework. We found evidence for senescence in survival with a continuous decline after the age of 1 year, but no evidence of reproductive senescence. Furthermore, we found no clear evidence for sex effects on these patterns. We discuss these results in light of previous studies documenting senescence in short-lived birds. We note that most of them have been conducted in populations breeding in nest boxes, and we question the potential effect of the nest boxes on the shape of age-reproductive trajectories.

Keywords: Saxicola rubetra; actuarial senescence; age‐specific demographic rate; aging; whinchat.

FIGURE 1

Age‐specific breeding success and survival in whinchats (both sexes combined). The lines represent the predicted relationship obtained from the linear models. The open dots show the age‐specific posterior means for breeding success and survival. The gray‐shaded area and the vertical lines represent standard errors. Sample sizes are placed over the dots. The graphs show the estimates from the UK population. The estimates for all other populations show the same patterns with age, but with a shift in the intercept

FIGURE 2

Male (left panel) and female (right panel) age‐specific breeding success in the whinchat. The plain lines represent the predicted relationships obtained from linear models. The open dots show the age‐specific posterior means. The gray‐shaded areas and the vertical lines represent ± standard errors. Sample sizes are placed over the dots

FIGURE 3

Male (left panel) and female (right panel) age‐specific annual survival in the whinchat. The plain lines represent the predicted relationships obtained from linear models. The open dots show the age‐specific posterior means. The gray‐shaded area and the vertical lines represent ± standard errors. Sample sizes are placed over the dots