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The defining innovation of the vertebrate stomach is acid-peptic digestion. The acidic stomach pH is produced by the gastric proton pump (H+ /K+ -ATPase) and proteolysis by the aspartic peptidase, pepsin. This provides advantages in protein digestibility and other key functions. Although highly conserved, secondary loss or regression has paradoxically occurred independently in multiple lineages primarily in the fishes. To better understand the role of gastric acidification and the consequences of loss, we developed the first non-mammalian knockout (KO) of the gastric proton pump by targeting the catalytic a-subunit (Atp4a) using CRISPR-Cas9 gene editing in the model teleost fish Astyanax mexicanus. We have set out to elucidate the impact of acid in digestion and nutrient assimilation, and on the molecular mechanisms involved in the gastric chloride and potassium movement. In the KO animals, gastric acidification was abolished with no adverse effects on specific growth rates and appetite although body protein, Ca, Mg and P were lower, and lipid was higher compared to wild-type. We also found a striking new role for the stomach in lipid uptake. RNAseq analysis was also performed and identified 2064 differentially expressed genes (DEGs) in stomach and 160 DEGs in anterior intestine of atp4a-/-  fish. The differentially regulated gastric and intestinal pathways in atp4a-/-  animals elucidate the impact of stomach acid in oxidative stress, and lipid and iron metabolism. Taken together, our results shed light on the role of the stomach in the processes of nutrient assimilation, opening the door to further analyses using this novel genetic line.

SEB Conference 2025

Will you miss me when I am gone? Gastric proton pump knock out and the importance of gastric acid in digestion, metabolism and growth in fish. 

gastrointestinal

pepsin

comparative physiology

gastric-peptic

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Animals care about multiple objectives, yet are stuck with one set of musculoskeletal parameters at a time. So, the question naturally arises, what values should they pick and what tradeoffs may they face? We cannot answer the first question as it is subjective, however we can attempt to answer the second. Here we focus on Achilles tendon stiffness – whose value in humans has been shown to maximize efficiency in walking and running. We ask how does changing Achilles tendon stiffness (1) affect efficiency, stability and economy of movement in a cyclic bouncy gait (e.g. hopping) and (2) how do they tradeoff. To answer that question, we built a mathematical model of human hopping which consists of a mass in gravity actuated by a muscle-tendon unit across a lever arm (representing the foot). The muscle is cyclically stimulated at 2.5Hz (preferred hopping frequency) to generate hopping and efficiency (ratio of mechanical work and metabolic cost), stability (average ratio of energy dissipated and energy injected by a change in ground height), and agility (maximum and minimum work possible by changing stimulation timing) were calculated. We find (1) Nominal achilles tendon stiffness (180000 N/m) had maximum efficiency, medium stability, and low agility ( positive work) and high agility (negative work). Additionally, increasing stiffness had no benefit except agility (positive work). However, decreasing stiffness trades off lower efficiency to gain higher agility (negative work) and higher stability – potentially explaining why older adults have lower tendon stiffness values despite the energetic burden.

Trading off stability, agility and efficiency of movement across a broad range of muscle tendon morphologies

Muscle inertia should affect the mechanical output of muscle, with its effects being greatest at larger sizes, and greater accelerations. Muscle inertia is known to affect the mechanical output of isolated muscle preparations; however, its influence during natural, whole-body movement remains unclear. In this study, forces were compared between a traditional one-dimensional massless muscle model , and a muscle model in which muscle mass was distributed along its length. Kinematic and electromyographic data were collected from twenty participants performing walking, running, hopping and sit-to-stand tasks, and muscle was geometrically scaled using factors of 0.1, 1 and 10. The results showed that muscles modelled at a scale factor of 10 exhibited significantly higher root-mean-squared errors (RMSE) in normalised time-varying forces, reaching up to 7.23% of maximum force for the vastus lateralis during running compared to a maximum RMSE of 0.31% for scales 0.1 and 1. Furthermore, tasks involving higher muscle accelerations, such as running and hopping, resulted in greater mass effects than lower-cadence activities. These mass effects were smaller than those we have previously predicted from 3D muscle models. These findings underscore the importance of accounting for muscle mass in larger muscles during rapid movements, and the need to account for complete 3D muscle deformations and dynamics when understanding muscle force and function.

Muscle Mass affects the scaling of Force Predictions from 1D Hill-Type Models During Human Movement

Muscle fibre type distribution may be influenced by clinical state and differs between individuals. For example, chronic heart failure patients experience a shift from fast to show fibres, while sprinters have a larger fraction of fast fibres than non-sprinters. However, in vivo changes in fibre type distribution are accompanied by alterations in other muscle properties, most notably size and strength, making it difficult to isolate their effects on movement. This challenge can be overcome using predictive simulations, which synthesize motion and control based on a performance criterion. This study investigated the impact of fibre type distribution on gait biomechanics using predictive simulations.
We simulated walking (1.33 m/s) using the predictive simulation framework, PredSim. Ninety-two muscles were each represented by a Hill-type muscle model with two motor units containing all its slow and fast fibres, respectively. The baseline model used experimentally derived physiological cross-sectional area fractions for slow and fast fibres. These proportions were then varied from 6% to 96% slow fibres to assess their effects on walking biomechanics.
Metabolic cost of transport gradually decreased (~26% in total) as the fractions of slow fibres increased from 6% to 96%. Spatiotemporal characteristics, joint angles, joint torques, and muscle coordination were similar in most conditions, excepting at the highest slow fibre fractions (>86% slow). While the latter effects were modest during walking, we hypothesize that fibre type composition may have greater impacts on more demanding tasks, such as running. Overall, these findings suggest that muscle fibre type composition meaningfully affects gait biomechanics.

Muscle fibre type distribution influences walking biomechanics: A predictive simulation study

Rapid global warming poses a serious threat to aquatic ectotherms. Evolutionary adaptation is a key mechanism that may enable populations to maintain performance under rising temperatures, yet it is rarely experimentally examined in vertebrates. Previous research in our laboratory demonstrated that zebrafish (Danio rerio) can evolve higher acute thermal tolerance, but this process is slow. Here, we present a large artificial selection experiment on zebrafish assessing the potential for adaptation of thermal growth performance. We selected zebrafish for improved juvenile growth across six generations under chronic thermal stress (N>10,800). Using a genetically diverse ancestral population (offspring of wild-caught zebrafish), we established selected lines (2 replicates, 300 fish/replicate) at cold (20°C), control (28°C) and warm (34°C) temperatures, and selected the 33% fastest-growing individuals for breeding. The results reveal a sustained, positive response to selection in all lines. Notably, the log growth rate of the warm-adapted line gradually increased from 0.008 to 0.013 mm/day in the F0  to F4  generation (total increase of 65%), reaching growth rates close that of the control line prior to selection, which suggests high evolvability. Ongoing analysis of the F5  generation will provide further insights into the evolution of thermal performance, including overall rates of adaptation, heritability, and shifts in optima. These results contribute to our understanding of how vertebrates may adapt to climate change and underscore the role of selection in shaping thermal resilience in aquatic species.

Artificial selection and the adaptive potential of thermal performance in zebrafish

The effects of climate change are expected to vary across aquatic habitats and geographic areas, so understanding how coldwater fish respond to warming below the species level will be essential for effective conservation and management. Brook trout, thermal generalists among salmonids, exhibit substantial phenotypic plasticity, giving rise to diverse ecotypes and life histories across their wide range, yet this diversity has not been captured in previous work on thermal performance. We investigated how brook trout from 14 populations with distinct ancestries, rearing environments, and life histories responded to thermal stress to elucidate the factors driving intraspecific variation in thermal performance. To do so, we quantified the metabolic plasticity of over 250 brook trout ranging from 46–448 mm (fork length) by briefly acclimating fish to either 15°C or 20°C in a laboratory setting. Standard and maximum metabolic rates were assessed both at their acclimated temperature and, without further acclimation, at the alternate temperature to evaluate aerobic scope under optimal and thermally challenging conditions. The differences detected in our study highlight the importance of examining thermal tolerance below the species level, as phenotypic plasticity, ontogeny, and heritable traits interact to shape resilience and the potential for adaptation in the face of environmental change.

Metabolic response to thermal change in fourteen populations of brook trout (Salvelinus fontinalis)

Mothers sometimes exhibit aggression towards their dependent offspring, a behaviour often linked to the weaning conflict, where such maternal behaviour could promote offspring independence. However, maternal aggression may also arise from genetic abnormalities or be induced by certain environmental factors. Yet, the biological mechanisms underlying maternal aggression and the interplay between genetic and environmental components remain poorly understood. Despite evidence suggesting that exposure to aggression may have stronger effects on genetically predisposed individuals.
To investigate possible biological mechanisms, we conducted an experiment in domestic canaries (Serinus canaria), a species in which mothers may exhibit maternal aggression (MA) towards their chicks. Full clutches were cross-fostered within and between MA mothers and no-MA mothers, creating four experimental groups to identify genetic and environmental influences. Juveniles were exposed to a series of behavioural tests, and we hypothesised that early MA exposure would increase impulsivity, reduce neophobia in a feeding context, and enhance aggression, potentially leading to higher dominance ranks. These effects should be amplified in individuals genetically predisposed to aggression.
We found that the relative importance of genes and environment varied across behavioural traits. Aggression-related traits and response inhibition were primarily driven by genetic factors, possibly reflecting a genetic component of MA. Dominance rank or food motivation were predominantly shaped by the early life environment influences, with poorer conditions in broods of MA mothers. In contrast to our expectations a gene-by-environment interactions was only found for neophobia, but it remains speculative how and why the results differ from the other behavioural traits.

Born to aggressive mothers - are certain chicks more susceptible to early life exposure to aggression

Early life environmental conditions are key fitness determinants that can modulate the expression of morphological, behavioral, and life-history traits. The impact of early life conditions is hypothesized to be reflected at the cellular level in the length of telomeres, the protective DNA structures at the ends of chromosomes. In many animal species, telomeres shorten with age and are related to individual life expectancy. Previous studies have also showed that telomere length is partly heritable, and that this trait is also potentially influenced by parental effects and environmental conditions. The aim of this project is to assess the genetic and environmental (e.g., temperature, brood size, and breeding habitat) determinants of telomere length in Tree Swallow (Tachycineta bicolor) nestlings. Our preliminary results suggest the presence of a genetic and/or a maternal effect influencing early-life telomere length. We also found significant differences in telomere length of nestlings among broods from different females , highlighting the need for further investigation into the determinants of this variability. This project will contribute to a better understanding of aging dynamics and life-history strategies across contrasting environmental conditions.

Determinants of early-life telomeres length in Tree swallows

As part of the Nature4Nature project “Inspired to Integrate: Filtering Nature's Diversity for Nature-friendly Implementations“, this study explores filter-feeding morphology in dabbling ducks for bioinspiration. Dabbling ducks, comprising approximately 70 species, exhibit diverse feeding morphologies and ecological adaptations. However, the relationship between their distinct filtering structures and dietary preferences remains poorly understood, particularly regarding the morphology of soft tissues and keratinized structures. These structures, including the lamellae on the upper and lower beak and the lingual papillae, are integral to filter-feeding on the water’s surface. This project aims to establish clear links between filtration behaviour, diet, and filtering apparatus morphology in dabbling ducks. Using CT-scans of 25 phylogenetically diverse duck specimens and macro photography of 13 dissected tongues, we conducted morphometric analyses to quantify filtering structure variations. Online databases such as Avonet were used to supplement ecological information, including dietary compositions and foraging behaviour. Comparative studies correlated the morphological variations with the ecological data, shedding light on how different filtering structures adapt to various dietary preferences and ecological niches. Our data suggest convergent evolution of tongue morphology for filter-feeding. This research will provide novel insights into dabbling duck filter-feeding mechanisms and the ecological drivers of their morphological diversity. This knowledge will provide new perspectives for the subsequent abstraction of the filter morphology and mechanism for the development of a bioinspired design performing a filter function.

The Art of Filter Feeding: Insights into the Feeding Morphology and Ecology of Dabbling Ducks 

Martin Becker and Stanislav Gorb
Department of Functional Morphology and Biomechanics, Zoological Institute, Kiel University, Am Botanischen Garten 1–9, D-24118, Kiel, Germany.
e-mail: mbecker@zoologie.uni-kiel.de
 
Abstract
The process of pollen release, transfer and capture is the most critical step in reproduction of higher plants and requires several steps of detachment and reattachment of pollen grains to different surfaces. As a response to their specific biotic or abiotic factors, pollen grains have developed strong variability of size, shape and surface microstructure, which affects their adhesion properties in a specific manner and contributes to the pollination syndrome of a plant. However, despite decades of research and a great public awareness, the adhesion forces have rarely been measured directly.
In the present study, we used a mass centrifugation setup with glass as a standard substrate, to characterize time dependent adhesion properties of pollen grains from four anemophilous species and compared them to the results of previous studies. Our results show strong differences in adhesion between species studied in fresh and aged state, which can be related to their respective pollination ecology. We discuss the species-specific adhesive properties of pollen grains in order to collect a broad set of quantitative data about adhesion properties of pollen grains and to understand their role in the process of pollination. The methodological aspects of the study are also discussed and centrifugation method is suggested as a standard approach for this kind of experiments.
 
Key words: adhesion, centrifugation, pollination, anemophily, plant, biomechanics

Time-dependent attachment properties of pollen grains in anemophilous plants tested by the mass centrifugation method

Autophagy is the evolutionarily well-conserved process during which cell components are degraded and recycled. One of the crucial, but poorly understood steps of autophagy is autophagic body degradation in vacuole. To this day, no enzyme involved in this autophagy stage in plants has been identified. However, vacuolar processing enzymes (VPE) constitute great candidates as they are key vacuolar enzymes that activate other hydrolases. Our team is addressing this hypothesis by conducting studies on isolated embryonic axes of white lupin (Lupinus albus L.) and Andean lupin (Lupinus mutabilis Sweet) cultured in vitro under various carbon (sugar) and nitrogen (asparagine) conditions. Sugar starvation induces autophagy, whereas asparagine (Asn) slows down autophagic body breakdown. So far, we detected a significantly higher VPE activity in sugar-starved axes (-S) than in sucrose-fed axes (+S), which was lowered in -S axes fed with asparagine (-S+Asn) and treated with autophagy inhibitors that interrupt this process at different stages. Ultrastructure observations, using a VPE inhibitor, showed an accumulation of autophagic bodies in the vacuoles of the -S axes. We performed the RNA-seq analysis and identified five transcripts of genes encoding VPE in each lupin species, within which four were most similar to the γVPE and one to the βVPE isoform of Arabidopsis thaliana. The RT-qPCR analysis revealed that only two γVPE-like genes showed higher levels of transcripts in the -S axes than in the +S axes. This may indicate that only given VPE participate in autophagic body degradation during sugar starvation-induced autophagy in lupin embryonic axes.

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