Condition-dependence in life history evolution

Abstract: Ageing is the progressive physiological deterioration that appears with increasing age and eventually leads to a decline in survival and reproduction. This physiological process is omnipresent across the tree of life, but the expected trajectory can widely vary between and within species. Classic theories predict that the evolution of senescence is strongly influenced by the level of extrinsic mortality. Furthermore, variation in early-life developmental environments can shape individual condition and thus lead to alternative life-history strategies. The interplay between early-life environment and individual condition might therefore predict the trajectory of ageing and is of importance when studying life history evolution. In this thesis, I focus on condition dependent life-history strategies and how this can translate in differential ageing patterns. Moreover, I specifically investigate the influence of early-life environment on key life history traits (i.e. survival and reproduction) and how this might eventually carry-over to future generations via nongenetic inheritance. First, I used an experimental approach involving lab populations of the nematode Caenorhabditis remanei to show that males, but not females, pay the cost for the evolution of increased lifespan (Paper I). Second, I used an empirical dataset based on 25 years of observations, to investigate the long-term effects of early-life environment on reproduction and survival (Paper II). Reproductive success of low-condition females in natural populations of collared flycatchers (Ficedula albicollis) peaks later in life, when high-condition females are already in steep reproductive decline and suffer from high mortality rates. Third, I used the neriid fly Telostylinus angusticollis in an experimental environment, to test whether condition-dependent investment in secondary sexual traits affects the life-history strategies of males (Paper III). High-condition males developed and aged faster than low-condition males, but interaction with rival males did not affect male reproductive ageing. Finally, continuing the T. angusticollis experiment, I also found that parental diet interacts with parental sex and offspring sex, ultimately affecting offspring life-histories. Parental effects can thus play an important role in shaping between-individual variation in reproductive and actuarial senescence (Paper IV). Overall, in this thesis I have explored the interaction between environment, condition and ageing in both experimental and natural settings.