Local adaptation in brown trout early life-history traits: implications for climate change adaptability

TLDR

Local adaptation of early life‑history traits in salmonids is increasingly important as climate change threatens populations that may lack the capacity to adjust to rising temperatures. This study examined whether four brown trout populations exhibit local adaptation in early life‑history traits. Populations spawning in rivers with distinct temperature regimes were reared in a common‑garden experiment at three temperatures to assess trait differentiation. Quantitative genetic differentiation exceeded neutral differentiation for two traits, temperature affected three traits, and population‑specific reaction norms plus heritable plasticity indicate that some trout may adapt to warming, though others could be negatively impacted.

Abstract

Knowledge of local adaptation and adaptive potential of natural populations is becoming increasingly relevant due to anthropogenic changes in the environment, such as climate change. The concern is that populations will be negatively affected by increasing temperatures without the capacity to adapt. Temperature-related adaptability in traits related to phenology and early life history are expected to be particularly important in salmonid fishes. We focused on the latter and investigated whether four populations of brown trout ( Salmo trutta ) are locally adapted in early life-history traits. These populations spawn in rivers that experience different temperature conditions during the time of incubation of eggs and embryos. They were reared in a common-garden experiment at three different temperatures. Quantitative genetic differentiation ( Q ST ) exceeded neutral molecular differentiation ( F ST ) for two traits, indicating local adaptation. A temperature effect was observed for three traits. However, this effect varied among populations due to locally adapted reaction norms, corresponding to the temperature regimes experienced by the populations in their native environments. Additive genetic variance and heritable variation in phenotypic plasticity suggest that although increasing temperatures are likely to affect some populations negatively, they may have the potential to adapt to changing temperature regimes.