Daphnia species are gaining interest as a model for ageing research due to characteristics such as easy generation of large clonal populations and short lifespan. Most interestingly, genetically identical female and male Daphnia have evolved different average lifespans, providing a unique opportunity for investigating sex differences in longevity to provide insight into the underlying mechanisms of ageing and regulation of lifespan. Data presented here begins to delineate these mechanisms. Significant differences between sexes in markers such as lifespan, growth rate, heart rate and swimming speed in addition to lipid peroxidation product accumulation, thiol content decline and age-dependent decline in DNA damage repair efficiency are reported. Furthermore, lipids play a significant role in regulation of health and disease. Here, dynamic changes in lipid composition as a function of age and sex are presented such as statistically significant age-related changes in triglycerides, diglycerides, phosphatidylcholine, phosphatidylethanolamine, ceramide and sphingomyelin lipid groups. Most interestingly, the rate and direction of change can differ between sexes, which could partly be the cause and/or the consequence of the different average lifespans between them. Transcriptome data also revealed rate and directional differences between sexes with age. Finally, evolutionary theories of ageing focus on genetic inheritance, but many observations suggest non-genetic inheritance also influences ageing phenotype. Here, findings show maternal age-effect on offspring. Importantly, the maternal age-effects can in part be recovered if subsequent generations are produced from younger mothers. Overall, this thesis supports that investigating sex differences in longevity in the clonal organism Daphnia under controlled laboratory conditions can provide insight into principal mechanisms of ageing and lifespan regulation.
Appendix 2 can be accessed on the University of Birmingham eData repository at: https://doi.org/10.25500/edata.bham.0000072
