Live fast, die old: oxidative stress as a potential mediator of an unexpected life‐history evolution

Abstract

Intraspecific latitudinal patterns in life history are well documented, yet underlying mechanisms of such patterns are poorly understood. To advance our insights in the evolution of latitudinal differences in two key traits, growth rate and lifespan, we evaluated the potential costs of rapid growth in terms of reduced adult lifespan, and the mediatory role of oxidative stress. We studied latitudinal differentiation in routine and experimentally increased (compensatory) larval growth rates, and in adult lifespan under common garden conditions in low‐ and high‐latitude populations of the damselfly Ischnura elegans. The low‐latitude populations showed not only higher routine growth rates but also a stronger compensatory growth response after a transient food shortage compared to the high‐latitude populations. In contrast with a tradeoff scenario, adults of the faster growing low‐latitude populations lived longer, had higher levels of antioxidant enzymes, and tended to experience lower oxidative damage. Importantly, these latitudinal patterns were largely mirrored at the treatment level, where experimentally induced compensatory growth rates were associated with neither oxidative damage nor shorter adult lifespans. Moreover, individuals with a higher growth rate after the transient food shortage did not have shorter adult lifespans or higher oxidative damage, but instead showed a stronger antioxidant defense. Our data indicate that an overcompensatory, hormetic response in antioxidant defense, potentially induced by the higher routine growth rates, resulting in less oxidative damage may underlie these unexpected growth‐lifespan patterns. Our results highlight the added value of incorporating oxidative stress physiology, and the need to consider multivariate tradeoffs in which animals optimize multiple traits, when studying life‐history evolution.