Plasticity of ageing in burying beetles

Abstract

Ageing is the progressive physiological deterioration and decline in performance with advancing age. Patterns of ageing are incredibly diverse both across and within species, with pronounced differences in how much and how quickly mortality, fertility and performance deteriorate over age. While the drivers of this variation are not yet fully understood, it is clear they have profound implications for our understanding of the evolutionary processes shaping ageing.

For example, early-life conditions may broadly be expected to shape adult phenotypes, with consequences for adult life-histories and patterns of ageing. However, life-history theories differ in their predictions for the late-life consequences of early hardship. This is particularly the case for important phenotypic traits that can underpin survival and reproduction, which are often overlooked in ageing studies.

Further, a great deal of our understanding of ageing has come from research on laboratory invertebrate populations. However, ageing is a highly plastic trait that is sensitive to biotic and abiotic environmental change and can be ecologically dependent. Natural populations face more hostile environments and are exposed to predation, starvation, immune challenge, competition, and a whole host of abiotic stresses from which their laboratory counterparts are protected. Despite broad acknowledgement that the environment can shape ageing, very few species have been studied in both laboratory and natural contexts.

In this thesis, I set out to explore drivers of variation in patterns of ageing, attempting to address the gaps in the current literature with respect to early-life environmental effects on patterns of actuarial, reproductive, and functional ageing, and the effect of broad shifts in environment (from the laboratory to the wild) on patterns of demographic and physiological ageing.

To this end, in Chapter 2, I examined the role of early-life food abundance in shaping ageing in flight performance in a laboratory population of burying beetles. In Chapter 3, I investigated the effect of parental loss on the developing phenotype and subsequent patterns of actuarial and reproductive ageing. In Chapter 4, I explored the effect that broad shifts in environment (the laboratory versus natural conditions) had on patterns of actuarial and physiological ageing. In Chapter 5, I outlined a workflow and python pipeline I developed to facilitate photographic record-based identification of individuals in mark recapture studies.

This chapter explains how individually-unique patterns present on the elytra of burying beetles can be leveraged as a means of individual recognition.

I found that while early-life food abundance can have age-independent effects on flight performance, there was no evidence that early-life conditions shaped ageing in these traits.

Further, I found that the presence or absence of maternal care during development played a role in shaping patterns of ageing and lifespan. In assessing in wild- and laboratory-living populations I found overall mortality was higher in the wild but that age-specific increases in mortality were only apparent in the laboratory-maintained population.