Abstract
1. Age-dependent increases in mortality have been documented in a variety of species of insect under laboratory conditions. However, while strong statistical evidence has been presented for senescence in vertebrate populations in the wild, we know little about the rate and shape of senescence in wild populations of insects. 2. Odonates (damselflies and dragonflies) provide excellent candidate species for evaluating demographic senescence as they are large enough to be marked individually and they are easily re-sighted without recapture. The prevailing opinion - based entirely on qualitative examination of the declines in log numbers alive with time since marking - is that odonates exhibit age-independent daily survivorship. 3. Here, we examine mark-recapture data on the Azure Damselfly Coenagrion puella over two consecutive seasons. For the first time, we evaluate and compare the fit of quantitative models that not only account for weather-dependent daily variation in daily re-sighting rates, but also age-dependent variation in daily survivorship. 4. Models with age-dependent declines in daily survivorship provide a more parsimonious explanation for the data than similar models without these age-dependent effects. In general, models in which mortality increases in an exponential (Gompertz) fashion explain the mark-recapture sequences more efficiently than a range of alternative models, including those in which mortality increases as a power function (Weibull) or reaches a plateau (logistic). These results are indicative of a general senescent decline in physiological functioning, which is particularly marked after 15 days as a mature adult. 5. Weather (temperature, sun and precipitation) and initial mite load influenced the probability of daily re-sighting. Weather and mite load also influenced daily survivorship, but their effects differed between seasons. 6. Overall, fitting models with age as an explicit covariate demonstrates that odonates do indeed senesce. This contradicts previously held assumptions that Odonata do not exhibit age-dependent survivorship in the wild.
Highlights
Senescence is the progressive deterioration in the physiological state of an organism, marked by an increase in mortality and ⁄ or decrease in fecundity over time
Odonates provide excellent candidate species for evaluating demographic senescence as they are large enough to be marked individually and they are re-sighted without recapture
Models in which mortality increases in an exponential (Gompertz) fashion explain the mark–recapture sequences more efficiently than a range of alternative models, including those in which mortality increases as a power function (Weibull) or reaches a plateau
Summary
Senescence is the progressive deterioration in the physiological state of an organism, marked by an increase in mortality and ⁄ or decrease in fecundity over time (see Partridge & Gems2002; Hughes & Reynolds 2005; Rose 2005; Bonsall 2006; Williams et al 2006; Sherratt & Wilkinson 2009 for recent reviews). A similar body of research exists for laboratory-reared insects (see for example Rose 1984; Stearns et al 2000; Carey 2001) These laboratory studies have generated a range of insights, including inspiring strategies to avoid the evolution of pesticide resistance in malarial mosquitoes (Read, Lynch & Thomas 2009). While laboratory studies on insect senescence have been conducted for decades, the only detailed studies of senescence in wild insects have all been published within the past 8 years Without such field studies it is not possible to evaluate the nature of selection acting on ageing under natural conditions, and the ecological validity of results from laboratory studies cannot be ascertained (Linnen, Tartar & Promislow 2001; Kawasaki et al 2008)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
