Factors affecting accumulation of lipofuscin age pigment in arthropod neural tissue and its use as an ecological tool for age determination
This project aimed to explore factors that modulate neurolipofuscin accumulation, using two experimental arthropod species, the locust, Locusta migratoria, and the freshwater crayfish, Pacifastacus leniusculus. The pattern of age-related accumulation of neurolipofuscin in L. migratoria was found to differ from that previously reported for crustaceans, with little accumulation prior to maturity and an exponential increase with high variability thereafter. It was shown, for the first time in any crustacean, that unilateral eyestalk ablation reduces neurolipofuscin accumulation rate in the contra-lateral eyestalk of P. leniusculus. It is hypothesized that this represents either reduced lipofuscinogenesis due to neurohormonal effects on oxidative catabolism or increased lipofuscin degradation by accelerated proteolysis following CNS damage. This finding means that longitudinal measurements of lipfuscin, i.e. in the same individual, by eyestalk biopsy, cannot be used to assessa natural lipofuscin accumulation rates in individuals of unknown age. Neurolipofuscin accumulation rate in ablated signal crayfish was found to be strongly inversely correlated with physiological age, with old individuals generally losing lipofuscin after ablation. Although this pattern is likely to be an artefact of ablation, it is the first quantitative evidence of in vivo reversibility of lipofuscin accumulation for any species and has important gerontological implications. Annual cohorts were detected by modal analysis of a neurolipofuscin concentration histogram for a pond population of P. leniusculus for the first time. Growth curves fitted to the length-at-age data obtained from this analysis were compared with results of three conventional methods for growth curve estimation: size-frequency analysis, anniversary tag-recapture and laboratory rearing. This analysis highlighted problems with extrapolation of growth rates from laboratory rearing to the field. Neurolipofuscin methodology is the only approach that can give age-length data for older individuals in the wild population and measurements of longevity.