France

Abstract: Forecasting the long-time consequences of global warming requires knowledge not just on thermal mortality but also how heat stress interacts with other environmental stressors1,2. Here we describe an analytical framework that combines laboratory measurements and high 
resolution field temperature records to      forecast      mortality 
risks over the next century. As a proof of concept, we study amphipods Dikerogammarus villosus and Echinogammarus trichiatus from river Waal, Netherlands, acclimated to different temperatures and oxygen levels. We predicted daily and annual heat mortality in the river under different 
oxygen levels for current temperatures      and for 1 ºC and 2 ºC 
warming     . Given the p     rojected increases in      summer 
temperatures,      annual mortality is forecasted to increase 
substantially during the next decades, varying with acclimation status 
and water oxygenation. Both      acclimation to elevated water 
temperatures and adequate oxygenation are      crucial for persistence 
under current temperatures. However, even in the best case scenario,     
  mortality in D. villosus is expected to approach 100 % by 2100, while E. trichiatus appears to be less vulnerable. Overall, this framework generates forecasts in unprecedented detail on short- and long-term temporal impacts of rising temperatures in ecological communities, and also the contribution of other environmental stressors.

SEB Annual Conference 2022

Long-term forecast of thermal mortality with climate warming in amphipods from a temperate river

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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

technical paper

Interactions between plants and herbivores are essential for land ecosystems, and their diversity is driven by an evolutionary arms race between plant defences and insect counteradaptations. Plants protect themselves against herbivory by chemical and physical defences, while many insects have evolved mechanisms to overcome these. Compared to chemical plant defences, little is still known about the role of physical defences and insect counteradaptations. We investigated the role of hooked trichomes in Passiflora adenopoda as a physical defence against herbivores and how certain Heliconius caterpillars can cope with these trichomes. Behavioural assays and video analysis showed that hooked trichomes of P. adenopoda arrested the movement of "generalist" H. melpomene caterpillars, and killed them by piercing their cuticle. Moreover, if H. melpomene caterpillars managed to ingest trichome-bearing leaves without external injuries, they still always died. As the caterpillars developed normally when fed with leaves where trichomes had been "shaved", this effect must be based on internal mechanical damage. We found that ingested hooked trichomes penetrated the gut peritrophic matrix in H. melpomene caterpillars. By contrast, "specialist" Heliconius charithonia caterpillars could easily crawl over the leaves by pulling their prolegs away from the trichomes. They also successfully fed on trichome-bearing leaves, likely due to modifications in their gut peritrophic matrix. Light and scanning electron microscopy of the caterpillars' cuticle and the gut peritrophic matrix revealed characteristic differences between both Heliconius species. Our study helps to understand an important but as yet little-explored aspect of the evolutionary arms-race between Passiflora and Heliconius

Game of thorns: How hooked trichomes protect plants from herbivory and how specialised

Atlantic killifish are found in estuarine habitats along the Atlantic coast of North America. In these habitats, fish are exposed to thermal variation at multiple scales - at timescales from days to seasons, and across latitudes, such that the northern subspecies is locally adapted to cold temperatures, and the southern subspecies to warm temperatures. The northern and southern subspecies differ substantially in mitochondrial properties, with mitochondria from northern fish having greater respiratory capacity, which likely helps to support their greater whole-organism aerobic metabolic rates. However, this pattern is only observed in mitochondria from the liver, and not in mitochondria from the heart or the brain, emphasizing the importance of examining mitochondrial properties across tissues. We also find differences in mitochondrial oxygen affinity between species (assayed in liver mitochondria), with mitochondria from southern fish having greater oxygen affinity, consistent with their superior whole organism hypoxia tolerance. In addition to the putatively adaptive variation, both subspecies demonstrate substantial plasticity in mitochondrial properties. Acclimation to high temperature results in a strong suppression of mitochondrial capacity in both subspecies, mediated upstream of cytochrome c oxidase, which may help to compensate for the effects of acute exposure to high temperature on reaction rates.  In contrast, acclimation to low temperatures causes relatively modest increases in mitochondrial capacity, but in the northern subspecies only, it also causes substantial increases in mitochondrial density. These data demonstrate the many ways that mitochondrial properties are shaped by both plasticity and adaptation in this small fish.

Plasticity and adaptation in mitochondrial function in killifish

Mitochondrial function [e.g., respiration, respiratory coupling ratio (RCR) and reactive oxygen species (ROS) production] is negatively impacted by high temperatures, and may limit fish cardiac performance and upper thermal tolerance. Nevertheless, direct evidence of this is lacking, and testing at different levels of organization will be critical to establishing whether this construct has validity. We acclimated salmon to 10 and 20°C for &gt;2 weeks and then: used strips from half of the ventricle to simultaneously measure muscle work and O2 consumption (and thus efficiency) at 20 and 26oC; and the other half to obtain myocardial homogenates and isolated mitochondria so that mitochondrial functional parameters could be measured at the same temperatures. State 4 respiration for isolated mitochondria and State 2 respiration for homogenates, and absolute ROS production during these states, were positively correlated with resting muscle O2 consumption in fish acclimated to both temperatures. In contrast, we were unable to consistently identify relationships between mitochondrial parameters and O2 consumption/efficiency while the muscle was working. For example, the P:O ratio (Complex I) and RCR (Complex I+II) for these preparations were not related to the absolute efficiency of shortening work. Further, while total CI+CII ROS production was negatively correlated with the efficiency of shortening work in 20oC acclimated salmon, this relationship was not evident for 10oC acclimated fish. These results: are consistent with previous data showing that warm acclimation improves cardiac mitochondrial function at high temperatures; but only provide a tenuous link between heart and mitochondrial performance in salmon under such conditions.

Are Cardiac Muscle Performance and Mitochondrial Function Related in Atlantic Salmon (Salmo salar) at High Temperatures?

There is a wealth of evidence for the impact that early-life conditions, e.g., differences in growth rate, have on individuals’ later-life phenotype and performance. Mitochondria are believed to be a key player in this, as they not only fuel the cellular processes but are also involved in health and age-related disorders. Birds have surprisingly slow ageing rates and long lifespans for their body size and physiology. Recent work with avian models has highlighted the utility of determining mitochondrial function in their nucleated red blood cells (RBCs), which enables longitudinal sampling of mitochondria within individuals as they age. Here, we employ this new perspective to test, using zebra finches (Taeniopygia guttata), whether modifying an individual’s postnatal growth trajectory, using an ecologically-relevant scenario, results in consistent changes in adulthood mitochondrial functioning and if these relate to individual’s survival. Our results demonstrate that within individual age-related changes in mitochondrial function can be detected using RCBs in birds and they are evident by middle age. However, despite that some of the mitochondrial traits show individual consistency, we found no link between adult RBCs mitochondrial function and the pace of early growth or mid-term survival. Further research across the life course will help to interpret the implications of the observed changes for individual performance and its sensitivity to environmental changes.

Can growth conditions predict adulthood blood mitochondrial function and survival?

In nature, organisms are faced with constant nutritional options which fuel key life-history traits. Studies have shown that species can actively make nutritional decisions based on internal and external cues. Metabolism itself is underpinned by complex genomic interactions involving components from both nuclear and mitochondrial genomes. Products from these two genomes must coordinate how nutrients are extracted, used, and recycled. Given the complicated nature of metabolism, it is not well understood how nutritional choices are affected by mitonuclear interactions. This is under the rationale that changes in genomic interactions will affect metabolic flux and change physiological requirements. To this end we used a large Drosophila mitonuclear genetic panel, comprising 9 isogenic nuclear genomes coupled to 9 mitochondrial haplotypes, giving a total of 81 different mitonuclear genotypes. We use a capillary-based feeding assay to screen this panel for dietary preference between carbohydrate or protein. We find strong levels of sexual dimorphism for this trait, with females consuming a lot more protein than males. Furthermore, we find significant mitonuclear interactions modulating nutritional choices. This work gives us deeper insights on how key metabolic interactions can have large implications on behaviour.

Mitonuclear interactions modulate nutritional preference

Inspired by avians, BirdBot legged robot utilizes mechanical intelligence, physically embedded in its leg structure and control. BirdBot features mechanical joint coupling to coordinate joint movements and power. Networks of overlapping spring tendons act as joint flexors and extensors, and complex functions are achieved. BirdBot shows robust, agile, and energy-efficient locomotion with surprisingly little control effort.  In stance, a spring-tendon network is engaged and acts on all leg joints with joint extending torques. The orientation of the toe segment purely mechanically engages this spring-tendon network. In the swing phase, the leg is slack, with no or minimal joint torques acting. During the swing, a knee motor flexes the slack knee joint. The remaining, slack joints follow the motion coordinated by the robot's tendon network. Both modes are designed to provide the leg's stance and swing phase functions, reduce energy consumption, reduce control effort, and increase the robot leg's performance. In this work, we closely observe the function of the robot's distal toe-flexor spring-tendon, which spans the two most-distal joints. The toe-flexor spring-tendon continuously charges in the stance phase, accumulating energy. At the stance-swing transition, the tendon collapses the TMP joint. This action rapidly switches the leg from its loadable stance phase to its slack swing mode and also pushes the toe segment into a digital-flexed posture. Hence, besides its main function as a clutch trigger, the toe flexor-tendon also recuperates mechanical energy back in the leg. Energy stored in stance is released and supports rapidly flexing and leg protraction.  

Biarticular toe-flexor tendon and its function depending on locomotion speed

Biomechanical computational models have been comprehensively used to evaluate the physiology of locomotion within various extinct and extant vertebrate species. Such models offer enormous potential to explore parameters which would otherwise require invasive procedures to measure experimentally, however, it is currently unknown which functional inputs are integral to developing physiologically and biomechanically accurate models. Amongst the most important models inputs, though often ignored, are the force-velocity characteristics of the muscle actuators, which describe the relationship between force-generating capacity during shortening and lengthening. While the shortening velocity of muscles has been extensively studied, fibre behaviour during lengthening is less well understood, and as such are not included in many muscle driven simulations of vertebrate movement. Here, we aim to use the ‘fast’ extensor digitorum longus and ‘slow’ soleus from the mouse to explore if there exist phenotypic differences in the lengthening portion of the force-velocity relationship and explore the functional implications these parameters have on the outputs of a biomechanical simulation of mouse trotting. Using in-vitro isovelocity contractions that span ±5% of optimum fibre length on the force-length relationship, we show that several aspects of the force-velocity relationship differ significantly between the muscles. Applying these muscle-specific force-velocity curves to the musculoskeletal model, we show that the predicted lengthening and activation parameters were highly sensitive to these input parameters, as was muscle power. These data highlight the importance of accurately representing the force-velocity relationship of muscles for the generation of physiologically valid musculoskeletal models.



Functional consequences of the force-velocity relationship on simulated musculoskeletal dynamics

Limb movements and their control are widely studied using musculoskeletal models, but the results of biomechanical simulations can be heavily influenced by the choice of muscle model. In order to investigate how reaching movements are affected by intrinsic muscle properties, we have implemented a simple upper limb model with three joints, each controlled by an antagonistic muscle pair. By varying the characteristics of the muscles in the model, we have studied the consequences of using a simple activation dynamics model compared to a more realistic, higher-order activation model, and we have also investigated how activation dynamics interact with the muscles’ force-length-velocity characteristics to affect reaching outcomes. Our simulations suggest that accurate reaching movements can be achieved with a variety of muscle models, but compared to simple activation models, higher-order activation dynamics requires longer prediction from a forward model and gives rise to a higher level of unplanned co-contraction of antagonistic muscle pairs. In line with prior work, the force-length-velocity properties of muscles were observed to enable stabilisation and smoothing of limb movements in simulations as well as to promote accurate reaching performance with the high-order activation model. Overall, our simulation results support the use of simple muscle models when only the behavioural outcome is of interest. However, the choice of muscle model can become critical when addressing questions related to neuromuscular control, as models capable of capturing realistic muscle behaviour may also affect key features of the control problem.

The impact of muscle activation dynamics and other intrinsic properties on reaching movements: A simulation study

Elucidating transcriptional regulatory networks requires knowledge of transcription factor (TF) binding sites and their occupancy, ideally in a native chromatin context. Towards this goal, we have adapted the use of micrococcal nuclease (MNase) as a biochemical probe of fixed chromatin structure with emphasis on small DNA fragments from sub-nucleosome-sized particles. Specifically, we developed MNase-defined cistrome-Occupancy Analysis (MOA-seq) to achieve high-resolution genome-wide detection of TF-bound sites within accessible chromatin regions, illustrated with a proof of concept study on field-grown maize ear shoots (Savadel, Hartwig, et al., 2021; PLOS Genetics). Fragment center plotting focused the footprint detection down to small particles with an average peak size of ~30bp. These MOA footprints (MFs) exhibited (1) expression-correlated associations with gene promoters, (2) enrichment at known TF-binding sites, (3) enrichment at known long-range chromatin interaction sites, and (4) enrichment at known open chromatin regions defined by other non-MNase assays such as ATAC-seq. Motif analysis of 145,000 maize earshoot MFs led to the detection of 215 sequence motif families, which were merged into non-overlapping regions numbering just above 100,000 loci and covering just below 0.1% of the maize genome. We also used MOA-seq to examine genomic response to hypoxia in human cells. From these initial studies, we conclude that MOA-seq is ideal for genome-wide identification of cistrome occupancy at high resolution using a single antibody-free assay. The technology adds a valuable method to the genomic toolkit for pinpointing cis-regulatory candidates in agriculture and medicine.

MNase-based MOA-Seq Pinpoints Native Cistrome Occupancy at 30-bp Resolution Amid Accessible Chromatin

The interaction between chromatin and the nuclear lamina (NL) is intrinsically important to the establishment of three-dimensional chromatin architecture and spatiotemporal regulation of gene expression. However, critical regulators involved in this process are poorly understood in plants. Here, we report that Arabidopsis PNET2 and its two homologs are bona fide inner nuclear membrane proteins and integral components of the NL. PNET2s physically interact with the plant nucleoskeleton and engage nucleosome-enriched chromatin at the nuclear periphery. Loss of all three PNET2s leads to severely disrupted growth and development, concomitant activation of abiotic and biotic stress responses, and ultimate lethality in Arabidopsis. The pnet2 triple mutant also displays drastic transcriptome changes accompanied by a globally altered chromatin architecture revealed by HiC analysis. Our study identified PNET2 as an inner nuclear membrane (INM) component of the NL, which associates with chromatin and plays a critical role in orchestrating gene expression and chromatin organization in plants.











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Long-term forecast of thermal mortality with climate warming in amphipods from a temperate river

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Game of thorns: How hooked trichomes protect plants from herbivory and how specialised

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