While hypoxia (i.e. low dissolved oxygen level in water) events occur naturally, global change and human activities have exacerbated their strength and temporal fluctuations. As populations may not be able to escape the hypoxic conditions, especially in freshwater ponds, it is crucial to understand how organisms can adjust and adapt to these fluctuating environments. When directly exposed, individuals may be able to adjust their phenotypes through plasticity, but continued exposure to hypoxia over generations may require adaptation and evolution. As the mitochondrial metabolism is the key component that fuel aerobic functions, the individual capacity to respond to the environmental change in oxygen availability is likely to rely on mitochondrial functions. Using two populations of wild three-spined sticklebacks (Gasterosteus aculeatus) exposed to different levels of hypoxia conditions in their natural habitats and experimentally exposed to fluctuating hypoxia (20% air saturation during the night and 100% during the day), we investigated the fish metabolic plastic and evolutionary response.  We showed adaptation in fish growth and metabolic rate, fish exposed to hypoxia in their natural habitats possessing higher metabolic capacity, but limited evidence for plasticity to the experimental conditions. These responses were supported by the muscle mitochondrial metabolism, for which similar adaptation were observed. However, no differences were observed in the brain mitochondrial metabolism, suggesting tissue specific response to environmental changes. Overall, these results highlight the capacity of fish to adapt environmental changes across generations, relying on mitochondrial adaptation.

Fish metabolic response to freshwater hypoxia: plasticity and adaptation

The selective harvest of individuals from wild populations constitutes one of the strongest and most widespread human-induced evolutionary pressures for natural populations. In addition to imposing strong selection on potentially heritable fitness traits, intensive harvest could also cause environmental changes in targeted population, such as a reduction in the population density, which could in turn affect the evolutionary potential of the traits in the populations. As metabolic rate is related to many of the biological functions in animals, interacting with growth, movements, and behaviour, selection on this trait could have important repercussions for wild populations. Using wild zebrafish as model species reared at two densities, and simulated trawling fishing pressure as selective harvest, we investigated the potential for harvest-induced evolution on metabolic rate and associated traits (growth, swimming, risk taking behaviour). We showed consistent capture of fish with lower metabolic rate, slower growth and slower swimming, regardless of density. As these traits had significant heritability, such harvest could lead to evolution of the populations over time. However, even though metabolic rate was phenotypically correlated to the other traits, no genetic correlations were observed between metabolic rate and either growth or swimming. Therefore, selection on metabolic rate is unlikely to induce indirect selection on the other traits and vice versa. The potential evolution of metabolic rate, growth and swimming under harvest would thus be more the result of independent direct selection on each trait rather than correlated selection.

The evolutionary impact of harvesting selection and population density on fish metabolic rate and associated traits

[![](https://assets.underline.io/uploads/markdown_image/1/image/c6cb5ab9ee4d6eb52fa684b0a1b15ea4.png)](https://zoom.us/rec/play/eAjh6NHKZe4e0Is7kkJXl8fWj0xAc-tcVidinsw4eoGsfzaICYFJdxRZQDJHsPN9uYC78JgfZFgDlQGl.jgY1h7umdro5nd4o?autoplay=true&startTime=1657090447000)
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Mitochondrial metabolim is increasing recognized as a key mechanism that influences animal perfomance and adaptation to environmental conditions. Mitochondrial metabolic traits can be very plastic, but consistent differences still exist among individulas. This is probably due to the convoluted nature of mitchondrial proteins encoded by two different genomes but also to the ability of animals to respond to these environmental cues. Accounting for variation in mitochondrial genotype and phenotype is thus required to fully grasp the role of mitochandra in a braod range of organisms experiencing environmental changes and to explain the source of consistent variation both between and within populations. In this session , we will review the current knowledge of adjustments and adaptations allowing different organisms to cope with their environment at the mitochondrial level.

A14: Mitochondrial plasticity and adaptation: proximate determinants and ultimate consequences for adjustments to environmental conditions

technical paper

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SEB Annual Conference 2022

2022 will find over 1500 experimental biologists from across the globe converging on the third-largest French city near the Mediterranean coast and the fastest-growing city in the country over the past 25 years - Montpellier, France

Metabolic rate reflects an organism’s capacity for growth, maintenance, and reproduction, and is likely to be a target of selection. This session aims to examine the evolutionary potential of metabolism, by exploring both the causes of its variation, such as environmental and genetic sources of variation, energy trade-offs and constraints, and the consequences of variation for fitness. We welcome all submissions that consider evolutionary aspects underlying phenotypic variation in metabolic rates, including, selection, heritability, and plasticity. 

Amelie Crespel

2

Presentations

Fish metabolic response to freshwater hypoxia: plasticity and adaptation

The evolutionary impact of harvesting selection and population density on fish metabolic rate and associated traits

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