Individuals change over their lifetimes, frequently showing increased performance early in life, followed by peak mid-lifespan, and then senescent declines. Whilst the occurrence of senescence is well established in wild populations, many fundamental aspects of the effects of ageing still require exploration. Thus we understand little about what causes differences in ageing patterns between different components of fitness, or between the sexes, or about associations in performance at different stages of life. Furthermore, the impact of social environment on ageing patterns remains largely unexplored, but may be especially important for highly social species such as cooperative breeders. Recent evidence also points to trans-generational effects of parental age on offspring performance in wild bird populations, with important implications for population dynamics. Finally, determining levels of genetic variance underpinning all of these aspects is an important but increasingly achievable goal for studies of wild populations.
The project would investigate patterns of ageing in an Australian passerine, the superb fairy wren (Malurus cyaneus), using an exceptional dataset from a long-term study population in the Australian National Botanic Gardens, Canberra. Superb fairy wrens are cooperative breeders in which breeding pairs may be assisted by several male helpers, typically offspring of earlier broods; they are also longer-lived than high-latitude northern birds that have attracted most study to date. Pedigree information indicates that rates of infidelity are almost unprecedented (86% of broods contain extra-pair offspring), generating exciting opportunities to test whether parental age effects are driven by the social or genetic father. The study population is also characterised by marked differences in cohorts in subsequent contributions to the population, with distinct patterns of demographic change over the past three decades. The project would therefore address a range of questions:
- How do survival and reproduction rates change across the life-span?
- What effect does the social environment generated by cooperative breeding have on ageing patterns, and how does selection on helping, via inclusive fitness benefits, change across the lifetime?
- Is there genetic variation for ageing patterns of different traits, and how is this correlated across the sexes?
- Is early life success traded off against late-life declines?
- How do early-life conditions affect subsequent performance, and what are the implications of cohort variation in success for population demography?
- What are the trans-generational effects of parental age on offspring performance, and are these likely to be genetically or environmentally based?
The project would be supervised by Prof. Loeske Kruuk and Prof. Andrew Cockburn at the Australian National University. It will involve fieldwork at the study site, and analysis of the 28-year data set on the study.