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

Abstract

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 fertilization to hatching affects various traits at the onset of the free-swimming stage (i.e. a comparison between 3.5 and 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.

Temperature during embryonic development in brown trout influences juvenile behaviour in encounters with predators

“…In this study, we showed that a temperature increase of 3°C during embryogenesis resulted in more active and aggressive brown trout fry. This result was the opposite of what we predicted, and it contrasts with those of Takatsu et al (2022) and Greenberg et al (2023). They found that increased temperature during egg incubation resulted in less distance moved by newly hatched brown trout fry in an open field test.…”

“…The differing results may also relate to how activity was defined (i.e. in Takatsu et al, 2022 andGreenberg et al, 2023 vs. in our study). Distance in an open field test mainly measures exploratory behaviour (Stewart et al, 2012), whereas in our study, time spent swimming likely related more to a trade-off between avoiding conspicuous behaviour and aggression towards the mirror image than exploration.…”

“…Differences in growth caused by embryonic temperature are still evident in adult salmon and also are reflected in reproductive traits . Recently, Durtsche et al (2021) reported that brown trout (Salmo trutta) juveniles incubated at elevated temperatures as eggs have lower metabolism than trout from eggs incubated at natural winter temperatures, which results in reduced activity and exploration (Takatsu et al, 2022).…”

“…Specifically, we tested how brown trout fry differed in their behaviour in encounters with predators. Based on the results from Durtsche et al (2021), Takatsu et al (2022) and Greenberg et al (2023) we predicted that incubation temperature would influence risktaking behaviour, such as swimming activity and aggression, and we expected that activity and aggression levels would be reduced by elevated temperatures. We also hypothesized that trout would exhibit anti-predator behaviours in the presence of piscivorous fish and that these responses would be more pronounced if trout had been subjected to predator cues as embryos.…”

“…Recently, Durtsche et al. (2021) reported that brown trout ( Salmo trutta ) juveniles incubated at elevated temperatures as eggs have lower metabolism than trout from eggs incubated at natural winter temperatures, which results in reduced activity and exploration (Takatsu et al., 2022).…”