France

The rate at which animals acquire and use energy is an important factor that affects many aspects of animal performance, including reproductive output and thermoregulatory capabilities. Therefore, understanding the factors limiting energy budgets has remained one of the central issues in ecological and evolutionary physiology. We used a unique experimental evolution model – lines of bank voles (Myodes glareolus) selected for high rate of swim-induced aerobic metabolism (VO2swim, A-lines), which evolved a 70% higher VO2swim than that observed in unselected control (C) lines – and asked how the BMR, reproductive output, and thermoregulatory capabilities evolved in response to the selection. After 25 generations, animals from the A-lines achieve over 30% higher forced running maximum metabolic rate than those from unselected, control (C) lines. The selection has also increased the forced running maximum metabolic rate by about 30%37. Voles from the A-lines spend more time on active swimming, and, unlike the C-line voles, during the swimming trial work up to their physiological performance limit they achieve during running. In these lines the animals have developed an increased metabolic capacity, and we tried to understand the mechanism behind it. 




SEB Conference 2022

The physiological effects of experimental evolution of aerobic exercise performance in bank voles

Metabolic rate is closely related to body size (body mass), but when mass increases, metabolic rate usually increases less. This allometric scaling relationship between metabolic rate and body mass is fundamental to biology and widely applied, but also one of the most debated concepts in integrative and comparative physiology, ecology, and evolutionary biology.

Several theories and hypotheses have been put forward to explain why and how metabolic rate scales with body mass, and why there appears to be variation in how steep this scaling relationship is among different taxa and physiological or ecological conditions (e.g. 'surface area', 'cell size', 'fractal distribution network', ‘dynamic energy budget’, and ‘metabolic-level boundaries’ theories or hypotheses). However, the lack of consensus on these important topics is a major barrier to our understanding of the pace at which organisms of different sizes and species expend energy and need to consume resources such as food and oxygen from the environment. It also limits our ability to predict how metabolic rate and body size (co)evolves, and how climate change affects metabolic demands and body sizes, as metabolic scaling exponents are used to model how these key organismal traits are affected by changing temperature and oxygen levels. The importance of metabolic scaling is clear, yet it remains one of the most controversial concepts in biology.

The overall aim of this satellite meeting is to bring together researchers working with metabolic scaling, to: (1) bring the field up to speed on state-of-the-art knowledge and research on metabolic scaling; (2) help understand how the vastly different views and opinions on metabolic scaling can persist despite more than a century of research (e.g. scaling in proportion to surface area or not, universal ¾-power scaling or not, governed by ecological vs. physical or geometric factors); and (3) identify and help streamline specific areas of research on metabolic scaling that will be particularly important for our further understanding of why and how metabolic rate scales with body size.

The meeting is being organised as part of the Animal Section of the SEB and will therefore have a focus on metabolic scaling of animals, but work on other organisms is welcome where this can provide insight into metabolic scaling in general.

Why and how does metabolic rate scale with body size?

The overall aim of this satellite meeting is to bring together researchers working with metabolic scaling, to: bring the field up to speed on state-of-the-art knowledge and research on metabolic scaling; help understand how the vastly different views and opinions on metabolic scaling can persist despite more than a century of research (e.g. scaling in proportion to surface area or not, universal ¾-power scaling or not, governed by ecological vs. physical or geometric factors); and identify and help streamline specific areas of research on metabolic scaling that will be particularly important for our further understanding of why and how metabolic rate scales with body size.

technical paper

SEB’s Annual Conference is celebrated for creating the perfect composition of research, new discoveries and collaborative connections. Be creative and innovative by exchanging ideas and knowledge with masters of biology from all over the world.

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.
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2022 found 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.

Life-history variation emerges due to trade-offs in energy allocation, suggesting energetics shapes life-history evolution. The Atlantic salmon (Salmo salar) exhibits high diversity in the age-at-maturity trait, which is largely controlled by two genomic regions, vgll3 and six6.  This simple genetic control of age-at-maturity enables implementing genomic prediction methods to test potential genetic correlations, and subsequent co-evolution, between age-at-maturity and physiological traits. Here, we tested how variation in these life-history genomic regions affect the central metabolic phenotypes: standard and maximum metabolic rates, and aerobic scope in juvenile Atlantic salmon. We found no evidence for covariation between standard metabolic rate and the two life-history loci. However, we found that one of the life-history loci affected the maximum metabolic rate and aerobic scope, and that the two loci showed physiological epistasis in the control of maximum metabolic rate. We then measured proxies of aerobic and anaerobic capacities from four tissues to study how tissue-specific energetics can mediate genetic variation in life-history.  The results help us to better understand the mechanistic basis of life-history variation as well as metabolic constraints on life-history evolution.

Insights to genetic associations of life-history and metabolic rate via large-effect loci in Atlantic salmon

While some traits such as body size are well known predictors of metabolism, the covariance between metabolism and other traits remains poorly resolved. There are good reasons to suspect that developmental mode (direct or indirect development) should covary with metabolic rate but this covariance has not been explored. We compiled published data for adult metabolic rates and developmental mode for 705 species of marine invertebrates across 13 phyla. Using a phylogenetically-controlled analysis, we found that adult metabolism is shaped by developmental mode – species with planktonic larvae have higher metabolic rates than those with aplanktonic development. This pattern is unaffected by adult size. We also found support for differential temperature-dependence of metabolic rate among developmental modes. Overall, our results suggest developmental mode shapes the physiology of marine organisms in ways that have gone largely unanticipated by theory.

Macroevolutionary patterns in metabolism and development

Reproductive success (and therefore selection) is ultimately related to how well an organism performs in the context of its environment. Performance reflects the interactive trade-off between physiological traits, behaviour, resource availability and mortality. Time-integrated field metabolic rate (FMR) captures the realised energetic cost of performing in a natural setting, accounting for multi-generational acclimation to the environmental and ecological context. In-situ measurements of FMR may be needed to fully appreciate the evolutionary significance of variation in metabolic traits. 

Here we draw on data compiled using a new emerging proxy capable of providing estimates of individual-level FMR together with experienced temperature and growth rate derived from the otoliths of marine fishes. We quantify the extent and nature of among- and within-species variation in FMR observed so far in marine fishes. Among other patterns we show that in most observed populations operating within their natural thermal range, realised FMR is relatively insensitive to temperature, with no clear relationship between individual-level variation in FMR and growth rate. However, temperature has a stronger effect on realised FMR during early juvenile life stages (including in the same individuals), implying that in fishes, thermal effects on selection may be stronger during early juvenile life history stages. 








Variation in field metabolic rates of wild marine fishes: thermal, ontogenetic, phylogenetic and macroecological drivers.

Changing the morphology of the plant vacuole depends on the integrity of the cytoskeleton. So far, only little is known about the nature of this relationship. The plant-specific Networked (Net) family of membrane-associated actin-binding proteins contains two members, Net4A and Net4B, which are of special interest since they localize to the tonoplast. Recently, we could show that Net4 modules the compactness of vacuoles and this in turn affects its space-filling function and eventually inhibits cell elongation and growth. Since the net4a net4b double mutant only has a mild phenotype and other NETs seems not to compensate, we expected a higher molecular complexity and searched for new interactors. Pull-down experiments followed by MS-MS identified several new interactors, potentially participating in the regulation of the vacuole-cytoskeleton interface.

The vacuole - cytoskeleton connection: a handle to regulate growth

The vacuole is a hallmark of the plant cell, generating turgor pressure and thus driving growth. Seed plant embryos also contain numerous specialised Protein Storage Vacuoles (PSV) which are repositories for the nutritional content of seeds. But how do these specialised PSVs form and what mechanism drives this process? Recent work has demonstrated that PSVs are formed by the remodelling of the single embryonic vacuole into many fragmented PSVs. The main constituent of these PSV are seed storage proteins (SSP).  We have shown that SSP undergo liquid-liquid phase separation forming a droplet within the vacuole and these SSP droplets can bend the tonoplast membrane. However, can this process of SSP phase separation drive fragmentation of a single embryonic vacuole into multiple PSV? Additionally, which proteins and conditions drive phase separation of SSP in the embryonic vacuole? We have identified and are characterising protein candidates for drivers of phase separation in the embryonic vacuole and determining their role in PSV biogenesis.

Its all just a phase: Phase separation driving organelle biogenesis.

In plant cells, cargo proteins destined to the vacuoles contain sequence specific information known as vacuolar sorting determinant (VSD) that is recognized and sorted by vacuolar sorting receptors (VSRs) to the vacuoles. To understand how VSR recognizes its cargos, our group have determined the crystal structures of the PA domain of Arabidopsis VSR1 in complex with the vacuolar sorting determinants (VSDs) of a protease aleurain [1] and a 12 S globulin cruciferin (CRU) 1 [2]. Structural comparison with the apo-form of VSR1-PA suggests that cargo-binding induces conformational changes in four regions of VSR1-PA. The VSDs bind to the cargo-binding loop consisting of a conserved motif of 95RGDCYF100. The invariant Arg-95 residue was found to be essential for receptor-cargo interactions and vacuolar sorting of cargo proteins. In vitro pull-down assay showed that VSR1 interacts with the C-terminal decapeptide sequences of CRU1, CRU4 and vicilin-like seed storage protein (VL) 22, but not with those of CRU2, CRU3, VL21 and VL43. Tagging the C-terminal sequences of CRU1 and VL22 to the secretary red fluorescent proteins are sufficient in redirecting the proteins to the vacuoles in Arabidopsis protoplasts. A P453A substitution converts the C-terminal sequence of CRU2 to a C-terminal VSD that is recognized by VSR1. Structural insights on receptor-cargo obtained could be useful in targeting recombinant proteins to protein storage vacuoles in seeds.

This work was supported by grants from the Research Grants  Council  of  Hong  Kong  Special  Administrative  Region,  China (CUHK14151416, C4041-18EF, AoE/M-05/12, AoE/M403/16, and C4033-19E) and The National Natural Science Foundation of China (91854201 and31670179) and by direct grants from The Chinese University of Hong Kong.

[1] Luo F. et al. (2014) “How vacuolar sorting receptor proteins interact with their cargo proteins: crystal structures of apo and cargo-bound forms of the protease-associated domain from an Arabidopsis vacuolar sorting receptor.” Plant Cell, 26, 3693-708
[2] Tsao H.E. et al. (2022) Structural insights into how vacuolar sorting receptors recognize the sorting determinants of seed storage proteins. Proc Natl Acad Sci USA, 119, e2111281119.




How cargo proteins are recognized and sorted to the vacuoles?

Cells typically remain relatively small, because if cells grow beyond a critical limit, the surface of the plasma membrane eventually ceases to accommodate intracellular needs. Compared to animals, plant cells can dramatically increase their size without the apparent need for surface furcation. The vacuole is the biggest plant organelle and has a space-filling function, allowing to occupy up to 90% of the cell volume (Löfke et al., 2015; Scheuring et al., 2016; Dünser et al., 2019). The dynamic regulation of vacuolar size allows plant cells to expand with little increase of the cytosol (Dünser et al., 2019; Dünser et al., 2022), maintaining a favorable cell surface to cytosol ratio during growth. Here we discuss subcellular mechanisms that ensure the coordination of cellular and vacuolar size expansions.

Coordination of growth in plants

Stomata are anatomical structures at the surface of leaves controlling gas exchanges between the plant and the atmosphere. The stomatal pore aperture is regulated by two specialized cells, the guard cells, having the capacity to reversibly change their volume and shape. The changes of the guard cells’ volume are under tight control of signaling cascades regulating the ionic transport processes across the plasma and the vacuolar membranes. In guard cells the vacuole can reversibly change its volume during the opening and closure of stomata. We have used a 3D reconstruction approach to visualize the dynamics changes subcellular compartments volumes in living guard cells. The method we developed allowed us to simultaneously quantify the volumetric modifications of the cytosol and the vacuole. Notably, we could follow modification of the subcellular organization in parallel with the ion transport dynamics at the plasma and vacuolar membranes. Our data show that the vacuole accounts for the whole guard cell volume changes. This suggests that the turgor changes of the guard cells are driven by the vacuole during stomata aperture. 

Subcellular volume changes in stomata opening: vacuolar vs cytosolic volume changes.

The centriole is an evolutionary conserved organelle that coordinates fundamental biological processes including cell division, cellular signalling and cell motility. This organelle, of 500 nm long and 250 nm in diameter is composed of about 100 different proteins, some of which have been associated with human diseases. How these proteins are organized at the level of the centriole architecture and how associated mutations could be involved in pathologies is still poorly understood. I will present the latest work from my laboratory, which tackle these fundamental structural cell biology questions using cryo-tomography, cell biology and our newly developed ultrastructure expansion microscopy (U-ExM) method.

Expansion microscopy for Structural cell biology: from centriole architecture to human diseases

Determining how plasticity of developmental traits respond to environmental conditions is a challenge that must combine evolutionary sciences, ecology and developmental biology. Developmental plasticity is defined as the ability of an organism to adjust its development depending on environmental signals, thus producing alternative phenotypes precisely adjusted to the environment. Yet the mechanisms underlying developmental plasticity are not fully understood yet. Determining how plastic developmental changes that occur in response to environmental conditions are coordinated at the physiological, cellular, and molecular levels is a challenge that must combine ecology with developmental biology. The mechanisms that underlie the development of alternative phenotypes are still unclear for many systems and is one major goal of ecological developmental biology or Eco-Evo-Devo. We observed that clownfish (Amphiprion percula) young juveniles have a different rate of white bar formation depending on the sea anemone species, their obligate symbiotic partner, in which they are recruited: white bars develop more rapidly when fish are recruited in Stichodactyla gigantea than in Heteractis magnifica. Because the sister species A. ocellaris acquire their adult color pattern during metamorphosis under thyroid hormone (TH) control, we asked whether developmental plasticity in bar formation was associated with alteration in TH status as these are the main hormones triggering metamorphosis in vertebrates. We found that thyroid hormones regulate white bar formation and that a shift in hormone levels, associated with ecological differences, results in divergent color patterns in different sea anemone species in which the young fish is recruited. Taken together our results suggest that TH control the timing of adult color pattern formation and that shifts in gene expression and TH levels are associated with ecological differences resulting in divergent ontogenetic trajectories in color pattern development. We recently observed that the phenotypic change observed not only concerns pigmentation but also energy metabolism. The evolutionary implications of these observations will be discussed

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Insights to genetic associations of life-history and metabolic rate via large-effect loci in Atlantic salmon

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