Below-threshold mortality: implications for studies in evolution, ecology and demography

Abstract

Evolutionary biologists, ecologists and experimental gerontologists have increasingly used estimates of age‐specific mortality as a critical component in studies of a range of important biological processes. However, the analysis of age‐specific mortality rates is plagued by specific statistical challenges caused by sampling error. Here we discuss the nature of this ‘demographic sampling error’, and the way in which it can bias our estimates of (1) rates of ageing, (2) age at onset of senescence, (3) costs of reproduction and (4) demographic tests of evolutionary models of ageing. We conducted simulations which suggest that using standard statistical techniques, we would need sample sizes on the order of tens of thousands in most experiments to effectively remove any bias due to sampling error. We argue that biologists should use much larger sample sizes than have previously been used. However, we also present simple maximum likelihood models that effectively remove biases due to demographic sampling error even at relatively small sample sizes.

Evidence for only two independent pathways for decreasing senescence in Caenorhabditis elegans

“…Further addition of various treatments, although extending average lifespan, had no significant effect on G. Few changes in the initial mortality rate (A) were detected. The lack of a significant finding is not surprising, as it has been shown that A is highly variable (Promislow et al 1999). CHIL increased A for both daf-2 and clk1/daf-2 worms on DR, and dietary restricted daf-2 worms had a decreased A compared to dietary restricted N2 worms.…”

Food availability affects adult survival trajectories depending on early developmental conditions

“…Our sample sizes more than fulfil the minimum requirements for fitting mortality models [47]. Of the various mortality models fitted to our data, the Gompertz model fitted best (electronic supplementary material, table S4).…”

Considerations on Temperature, Longevity and Aging

“…In poikilotherms the effects of CR and temperature on longevity can be distinguished by the slopes of the mortality curves [19][20][21][22][23]. In Drosophila, chronic CR results in a delay in the onset of a detectable aging-related increase in mortality.…”