Divergence in pace-of-life in experimentally evolved seed beetles

Sammanfattning

Life history strategies are shaped both by trade-offs and physiological constraints limiting possible trait combinations. The pace-of-life syndrome (POLS) proposes that these constraints and trade-offs cause life history, physiological and behavioural traits to covary along a fastslow continuum. Resting metabolic rate (RMR) can indicate the pace-of-life (POL), which is where a species, population or organism falls on the slow-fast life history continuum. In this study, I phenotyped beetles from early reproduction (E) and late reproduction (L) experimental evolution regimes of the seed beetle Callosobruchus maculatus which have been evolving under different ecological conditions for approximately 190 generations. I tested divergence in POL in E and L regimes by comparing lifespan, total fecundity, reproductive timing, body mass, RMR, RQ (respiratory quotient) and allometric scaling coefficient. Sex differences were also assessed to determine potential differences in POL and potential sex by regime interactions. Here, I provide strong evidence that the E regime follows a fast POL and the L regime follows a slow POL. E was associated with a shorter lifespan, an earlier reproductive schedule, a lower body mass and a higher RMR compared to the L regime, while no evidence was found for divergence in total fecundity, RQ or allometric scaling coefficient. Males had a slightly longer lifespan, lower body mass and higher RMR, with the lifespan difference likely caused by using mated beetles rather than indicating a faster POL. The difference in body mass and RMR provides some evidence of a faster POL in males though the evidence for this is weaker than the evidence for POL divergence between regimes. There was no evidence of regime by sex interactions. Overall, the main differences between regimes were related to POL while there was no evidence for a divergence in other traits such as total fecundity, RQ or allometric scaling coefficient. The combined differences in life history traits and RMR between regimes provide evidence for POLS as the traits covary on a fast-slow continuum.