Reduced physiological plasticity in a fish adapted to stable temperatures

Publisher Copyright: Copyright © 2022 the Author(s).Plasticity can allow organisms to maintain consistent performance across a wide range of environmental conditions. However, it remains largely unknown how costly plasticity is and whether a trade-off exists between plasticity and performance under optimal conditions. Biological rates generally increase with temperature, and to counter that effect, fish use physiological plasticity to adjust their biochemical and physiological functions. Zebrafish in the wild encounter large daily and seasonal temperature fluctuations, suggesting they should display high physiological plasticity. Conversely, laboratory zebrafish have been at optimal temperatures with low thermal fluctuations for over 150 generations. We treated this domestication as an evolution experiment and asked whether this has reduced the physiological plasticity of laboratory fish compared to their wild counterparts. We measured a diverse range of phenotypic traits, from gene expression through physiology to behavior, in wild and laboratory zebrafish acclimated to 15 temperatures from 10 °C to 38 °C. We show that adaptation to the laboratory environment has had major effects on all levels of biology. Laboratory fish show reduced plasticity and are thus less able to counter the direct effects of temperature on key traits like metabolic rates and thermal tolerance, and this difference is detectable down to gene expression level. Rapid selection for faster growth in stable laboratory environments appears to have carried with it a trade-off against physiological plasticity in captive zebrafish compared with their wild counterparts.Peer reviewe

Thermal performance in zebrafish (Danio rerio) - Thermal acclimation capacity in wild and domesticated zebrafish

In times of imminent threat of climate change, clear evidence of which physiological mechanisms are limiting thermal performance remains scarce. This thesis involved measuring different performances, over a wide range of temperatures, and included a comparison between wild and lab-strain zebrafish (Danio rerio). We hypothesised that thermal optima of different performances will vary like in the multiple performance multiple optima model (MPMO, Clark et al., 2013; Gräns et al., 2014), and that the lab-strain zebrafish, which have been selected to optimise performance at 25-28°C since the 70´s, have reduced the capacity to acclimate to non-optimal temperatures. To test this hypotheses, we performed a pilot study, and two large-scale acclimation experiments on zebrafish, one in summer (n=560) and one in fall (n=600) of 2017. We measured a range of performances including survival, growth rate, acute thermal tolerance (CTmax), and swimming speed. In the pilot and the first acclimation experiment only wild-caught F1 generation zebrafish from India (n=560) were used. Half of the fish used in the second experiment were wild-caught F1 zebrafish (n=300), and the other half were from a lab-strain (AB-WT line, n=300). Both acclimation experiments lasted at least for four weeks to temperatures ranging from 10°C to 36°C/38°C with a difference of 2°C between each, after final temperatures were reached. Mortality differed between all experiments but was especially higher at the upper end of the thermal spectrum. Generally, lab fish displayed higher specific growth rates across temperatures than wild fish. CTmax rose with acclimation temperature in all populations but lab fish showed a lower CTmax at colder acclimation temperatures when compared to the wild population. CTmax was close to equal from temperatures above 26°C. Also, wild fish displayed a better swimming performance at highest temperatures, while the optima of the lab-strain was around 26 to 28°C. Lab-strain zebrafish appear to have maintained their capacity for some performances, e.g. survival and growth, during thermal acclimation, even after decades of adaptation to constant optimal temperatures. Overall the results still suggest a reduced acclimation capacity in lab-strain fish, and also shows varying optima to growth performance in wild zebrafish. Whilst more research is needed to fully investigate the first hypothesis, this thesis adds valuable information on varying optima between growth and swimming speed data, which will differ no matter how metabolic scope would turn out

Are model organisms representative for climate change research? : Testing thermal tolerance in wild and laboratory zebrafish populations

Model organisms can be useful for studying climate change impacts, but it is unclear whether domestication to laboratory conditions has altered their thermal tolerance and therefore how representative of wild populations they are. Zebrafish in the wild live in fluctuating thermal environments that potentially reach harmful temperatures. In the laboratory, zebrafish have gone through four decades of domestication and adaptation to stable optimal temperatures with few thermal extremes. If maintaining thermal tolerance is costly or if genetic traits promoting laboratory fitness at optimal temperature differ from genetic traits for high thermal tolerance, the thermal tolerance of laboratory zebrafish could be hypothesized to be lower than that of wild zebrafish. Furthermore, very little is known about the thermal environment of wild zebrafish and how close to their thermal limits they live. Here, we compared the acute upper thermal tolerance (critical thermal maxima; CTmax) of wild zebrafish measured on-site in West Bengal, India, to zebrafish at three laboratory acclimation/domestication levels: wild-caught, F-1 generation wild-caught and domesticated laboratory AB-WT line. We found that in the wild, CTmax increased with increasing site temperature. Yet at the warmest site, zebrafish lived very close to their thermal limit, suggesting that they may currently encounter lethal temperatures. In the laboratory, acclimation temperature appeared to have a stronger effect on CTmax than it did in the wild. The fish in the wild also had a 0.85-1.01 degrees C lower CTmax compared to all laboratory populations. This difference between laboratory-held and wild populations shows that environmental conditions can affect zebrafish's thermal tolerance. However, there was no difference in CTmax between the laboratory-held populations regardless of the domestication duration. This suggests that thermal tolerance is maintained during domestication and highlights that experiments using domesticated laboratory-reared model species can be appropriate for addressing certain questions on thermal tolerance and global warming impacts

Are model organisms representative for climate change research? Testing thermal tolerance in wild and laboratory zebrafish populations

Model organisms can be useful for studying climate change impacts, but it is unclear whether domestication to laboratory conditions has altered their thermal tolerance and therefore how representative of wild populations they are. Zebrafish in the wild live in fluctuating thermal environments that potentially reach harmful temperatures. In the laboratory, zebrafish have gone through four decades of domestication and adaptation to stable optimal temperatures with few thermal extremes. If maintaining thermal tolerance is costly or if genetic traits promoting laboratory fitness at optimal temperature differ from genetic traits for high thermal tolerance, the thermal tolerance of laboratory zebrafish could be hypothesized to be lower than that of wild zebrafish. Furthermore, very little is known about the thermal environment of wild zebrafish and how close to their thermal limits they live. Here, we compared the acute upper thermal tolerance (critical thermal maxima; CTmax) of wild zebrafish measured on-site in West Bengal, India, to zebrafish at three laboratory acclimation/domestication levels: wild-caught, F1 generation wild-caught and domesticated laboratory AB-WT line. We found that in the wild, CTmax increased with increasing site temperature. Yet at the warmest site, zebrafish lived very close to their thermal limit, suggesting that they may currently encounter lethal temperatures. In the laboratory, acclimation temperature appeared to have a stronger effect on CTmax than it did in the wild. The fish in the wild also had a 0.85–1.01°C lower CTmax compared to all laboratory populations. This difference between laboratory-held and wild populations shows that environmental conditions can affect zebrafish’s thermal tolerance. However, there was no difference in CTmax between the laboratory-held populations regardless of the domestication duration. This suggests that thermal tolerance is maintained during domestication and highlights that experiments using domesticated laboratory-reared model species can be appropriate for addressing certain questions on thermal tolerance and global warming impacts

Reduced physiological plasticity in a fish adapted to stable temperatures

Publisher Copyright: Copyright © 2022 the Author(s).Plasticity can allow organisms to maintain consistent performance across a wide range of environmental conditions. However, it remains largely unknown how costly plasticity is and whether a trade-off exists between plasticity and performance under optimal conditions. Biological rates generally increase with temperature, and to counter that effect, fish use physiological plasticity to adjust their biochemical and physiological functions. Zebrafish in the wild encounter large daily and seasonal temperature fluctuations, suggesting they should display high physiological plasticity. Conversely, laboratory zebrafish have been at optimal temperatures with low thermal fluctuations for over 150 generations. We treated this domestication as an evolution experiment and asked whether this has reduced the physiological plasticity of laboratory fish compared to their wild counterparts. We measured a diverse range of phenotypic traits, from gene expression through physiology to behavior, in wild and laboratory zebrafish acclimated to 15 temperatures from 10 °C to 38 °C. We show that adaptation to the laboratory environment has had major effects on all levels of biology. Laboratory fish show reduced plasticity and are thus less able to counter the direct effects of temperature on key traits like metabolic rates and thermal tolerance, and this difference is detectable down to gene expression level. Rapid selection for faster growth in stable laboratory environments appears to have carried with it a trade-off against physiological plasticity in captive zebrafish compared with their wild counterparts.Peer reviewe