No Evidence That Life History Strategies Shape Within-Body Mosaics of Ageing

Tissues across the body may age at different rates, which creates within-body mosaic ageing. Life history strategies shape ageing patterns at the inter- and intra-specific level, but the impact of life history strategies on mosaic-ageing patterns within individuals remains unknown. Reproductive tissues in individuals selected to prioritise reproduction may age faster than somatic tissues because of increased 'wear and tear'. Alternatively, individuals that prioritise reproduction may specially protect reproductive tissues at the expense of somatic tissues to allow for increased reproductive function. Here, we used Japanese quail (Coturnix japonica) artificially selected for increased versus reduced reproductive investment (egg size) to test how reproductive strategies modulate within-body variation in ageing patterns, by measuring telomere length as an ageing biomarker in blood cells, spleen and reproductive tissue (oviduct and testis). Although there were absolute, sex-specific differences in telomere length across tissue types, we did not find evidence that an individual's reproductive strategy shapes within-body mosaics of ageing: patterns of relative telomere length in somatic and reproductive tissues were similar in individuals selected for high and low reproductive investment, respectively (i.e., no significant selection regime × tissue type interaction), and consistent strong positive correlations in telomere lengths among blood cells, spleen and reproductive tissue were observed within individuals across reproductive investment selection regimes. Our results suggest that an individual's life history strategy does not affect tissue-specific ageing rates or that 'wear and tear' and 'special protection' mechanisms might act simultaneously and cancel each other out.