Repeated elevational clines of early life-history traits and their proximate mechanisms in brown trout

1. Climate warming imposes a severe threat to freshwater ecosystems, which are dominated by ectotherms such as fish and aquatic insects. To better predict the effects of climate warming on thermally sensitive ecosystems, information on how temperature affects individual traits within populations is fundamental. 2. Patterns of intraspecific variation in thermal reaction norms along geographic thermal gradients provide valuable information. Immediate temperature effects on individual traits can be inferred from the shape of the thermal reaction norm. The way that temperature and associated environmental conditions (to which populations have been exposed over generations) affect individual traits through transgenerational plasticity in, and/or natural selection on, these traits can also be inferred from patterns of trait variation along a geographic thermal gradient. 3. Many studies have documented patterns of intraspecific variation in thermal reaction norms along geographic thermal grad..., ,