Temperature regime during embryogenesis alters subsequent behavioural phenotypes of juvenile brown trout

Climate warming imposes a serious threat, especially to freshwater
ecosystems in temperate and (sub)polar regions, which are often dominated
by cold-adapted ectotherms. Although relatively intense warming during
winter is common across the climatic regions, comparably little focus has
been put on the organismal impacts of winter warming. Embryonic
development, which is exceptionally susceptible to ambient temperature,
occurs during winter in various freshwater ectotherms. Yet, our knowledge
of the effects of increased temperature during embryogenesis on later life
stages is limited. Using brown trout (Salmo trutta), we examined how a
1.5°C temperature increase from fertilisation to hatching affects various
traits at the onset of the free-swimming stage (i.e., a comparison between
3.5°C or 5.0°C treatments). Although all hatchlings were kept at the same
temperature (7.0°C) from hatching to the onset of the
free-swimming stage for about two months, the temperature increase during
embryogenesis substantially reduced key ecological
behaviours, i.e., activity and exploration levels, at the onset of the
free-swimming stage despite only marginal temperature effects on
morphological and physiological traits at this stage. Given the importance
of behavioural traits in early growth and survival, our study suggests a
likely pathway through which subtle changes in mean winter temperature
affect early fitness.