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The rabbit is a widely used model system in comparative and clinical sciences for understanding correlations between anatomy and function in the masticatory system. Experimental and simulation studies have hypothesised that the rabbit is able to modulate chewing mechanics to process a variety of food types with high efficiency. Through synchronously measuring 3D jaw motions (using biplanar x-ray videography), muscle length change (using fluoromicrometry) and muscle activity (using electromyography) during feeding on foods of varying material properties and maximum bite-force in-situ experimentation we have begun to test these hypotheses. Processing tougher food types resulted in an increase in whole chew-cycle duration, and particularly in the slow-closing proportion of chewing. Additionally, working side muscles appear to be recruited more during feeding on tougher food types. Finally, the capacity to generate force varies greatly over the entire gape cycle, with rabbits working at the lower end of the gape-force relationship. Our data suggest that the masticatory system modulates power output through two mechanisms, primarily through changes in masticatory frequency, specifically modulating the power stroke phase of the chew cycle, while also modulating muscle recruitment. Finally, our preliminary in-situ data suggests the rabbit functions outside the optimal range of the force-gape relationship. 

SEB Annual Conference 2022

The dynamic role of rabbit masticatory apparatus during feeding

Discover the art of creating extraordinary science at SEB’s Annual Conference at Le Corum Conference Center     in Montpellier, France from 5 to  8 July 2022.

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 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

poster

Bipeds provide a unique study system to address hindlimb allometry both across and within archosaurs and mammals — having size ranges spanning five orders of magnitude yet overlapping near 1 kg body mass for most major clades. Previous work on non-avian and avian theropods shows that hindlimb proportions cluster within 1/9th of available morphospace, centered around a 60:40 tibia:femur isoline. Here we expand on previous work by including bipedal hopping mammals and examining potential drivers of divergence. We investigate 1) within group scaling, 2) phylogenetic signal, and 3) differences between hopping and striding bipeds. Our avian analysis includes 374 species, spanning 74 families and 17 orders. Our mammalian analysis is restricted to habitual bipedal hoppers and includes 47 species distributed across 5 families and 2 orders. Prior to phylogenetic correction, significant hindlimb positive allometry is seen in Anseriformes, Gruiformes, and Palaeognathae, while significant allometry of some individual segments is found in nearly all avian clades. For mammals, significant positive allometry is seen in Macropodiformes but not Rodentia. After phylogenetic correction using PGLS, significant positive allometry persists in the metatarsal segment of Galliformes, Gruiformes, Palaeognathae, and Diprotodontia. (Macropodiformes exhibited positive allometry of the hindlimb, tibia, and metatarsals after PGLS.) Examining segment proportions revealed negative allometry of the femur with respect to total hindlimb length in these same groups. Hence, whether striding or hopping — avian or mammalian, significant positive allometry of the distal segment is a hallmark of both birds and mammals.

Variable scaling of limb segment proportions in bipeds: Does allometry drive divergence?

During flight, insects can make subtle changes to their wing kinematics that in turn have large effects on their aerodynamic forces. To understand and model the above, therefore requires measurements of natural flight with appropriate spatiotemporal resolution and duration. These factors are determined by wingbeat frequency, size, and behaviour, which are limited by trade-offs within the operating equipment. Here, we describe a new and flexible arena setup that uses ten high-speed cameras to record insects flying freely in an optically clear chamber that can scale from the smallest to some of the largest insects. Pulsed far-red LEDs are focused and aligned with the high-speed cameras to provide bright, uniform backgrounds that eliminate motion blur and are beyond the insects’ visible spectrum. Separate, stereo cameras function as triggers, using real-time image analysis when subjects enter the recording volume. These triggers can control additional stimuli, such as a white light, to induce flight manoeuvres at specific times. The resultant footage is coupled with a comprehensive voxel-carving software package to automatically calculate wing and body kinematics. This includes wing deformations in the form of wing torsion, which is important for accurate aerodynamic modelling. To date, we have documented  free-flight in several species, including Calliphora vicina and Drosophila melanogaster at 6,400 fps, and Anopheles gambiae at 12,000 fps. This setup will generate a large database of high-precision insect free-flight kinematics to better our understanding of this diverse class and be used to feed into studies of insect flight control and aerodynamics.

High-precision insect wing and body kinematics acquisition using a new and flexible free-flight arena

Boxfish (Ostraciidae) have peculiar body shapes, with conspicuous keels formed by their bony carapaces. Previous studies have proposed various hydrodynamic roles for these keels, including reducing drag during swimming, contributing to passive stabilisation of the swimming course, or providing resistance against roll rotations. We tested these hypotheses using computational fluid dynamics simulations of five species of Ostraciidae with a range of carapace shapes. The hydrodynamic performance of the original carapace surface models, obtained from laser scanning of museum specimens, was compared with models where the keels had been digitally reduced. The original carapaces showed no reduced drag or increased passive stability against pitch and yaw compared to the reduced-keel carapaces. However, consistently for all studied species, a strong increase in roll drag and roll added mass was observed for the original carapaces compared to the reduced-keel carapaces, despite the relatively small differences in keel height. In particular, the damping of roll movement by resistive drag torques increased considerably by the presence of keels. Our results suggest that the shape of the boxfish carapace is important in enabling the observed roll-free forward swimming of boxfish and may facilitate the control of manoeuvres.

The hydrodynamic function of keels in boxfish

When terrestrially locomoting, birds tend to swing the foot with the toes together, and then spread the toes prior to touch down, creating a larger surface area over which to spread the bird’s weight. However, on deformable substrates, particularly on very soft substrates like saturated mud, the ground does not fully, nor immediately bear the weight of the animal. Instead, the foot (and therefore bird) will sink some distance before finding support. We used X-ray Reconstruction of Moving Morphology to measure the digit divarication angle, or the spread of the toes, throughout the swing and stance phase of a Guineafowl walking over a solid surface, firm mud, and soft mud (11 trials). Maximum digit spread was slightly larger (82°) on soft mud compared with solid (71°) and firm mud (68°). However, our data show that at touchdown, digit divarication angle is more variable on soft substrates than firm ones. This indicates that in some cases, when the substrate is softest, the toes are still spreading as the foot sinks into the mud. We also found that digit divarication angle was much greater at mid stance when traversing soft mud than firm mud. Our data provide an interesting touch-stone for interpreting motions from deep dinosaur tracks, which may only present the surficial foot-sediment interaction. 

How digit divarication angle changes at touchdown and midstance as guineafowl traverse solid and deformable substrates.

Animal bite force is an ecologically relevant performance trait, crucial for individual fitness through its impact on food ingestion and intraspecific agonistic interactions. Despite its popularity in vertebrates, bite force has only recently begun to be measured across the huge diversity of insects. Bite force studies generally use either in vivo measurements or forces modelled based on muscle physiological cross-sectional area (PCSA), and very rarely compare both. PCSA can be measured in a variety of ways, in particular in insects, which have never been thoroughly compared. Here we compare several digitally computed estimates of PCSA (and its components muscle volume and fiber length) in the major mandibular adductor muscle of Schistocerca gregaria, together with an experimental baseline estimate. This experimental estimate relies on dissecting out the muscles, weighing them, dissolving fiber bundles in acid and measuring fibre length. The digital estimates are based on CT scans of the heads, in which it is possible to measure muscle volume, fibre length, and muscle attachment area. After scanning the heads of the specimens and segmenting their mandibular apparatus, we used manual and automated approaches to measure the above mentioned values, to assess the comparability of the various PCSA methods and proxies, as well as the reliability of the automatization process. In addition, using the different PCSA estimates and muscle stress values from the literature, we model bite forces, which we compare to in vivo measurements from the same individuals.

Modelling bite force in insects: comparison of different PCSA approaches with in vivo measurements

Rice (Oryza sativa L.) is one of the important cereal grains and a staple food for more than 50% of the world’s population. Increases in global temperatures have a negative impact on crop productivity. Plants undergo a variety of physiological and biochemical changes as a result of temperature stress in order to adapt to higher temperatures. In this study, we have used 204 accessions from the Bengal and Assam Aus Panel (BAAP). A total of eight replicate plant per accession were grown. All plants were grown in the greenhouse until maturity; thereafter, five replicate plants were randomly selected, their panicles at anthesis stage marked and were transferred to large growth room at 38°C for 24 hours to assess high-temperature treatments. Three replicates plants were not heat treated. Fertility was assessed as the proportion of flowers filled. Heat treatment significantly (P&lt;0.0001) reduced fertility by 17.4% on average and there was a significant (P&lt;0.0001) differences among accessions. In addition to that, there was a significant (P&lt;0.001) interaction between accession and treatment. Heat tolerant cultivars have been identified including the aus reference cultivar DJ123. Genome Wide Association Studies (GWAS) using 2 million SNPs will be used to identify QTLs and candidate genes associated with heat tolerance in the BAAP.

Genotypic Variation in Heat Tolerance in Aus Rice During the Flowering Stage 

The Arabidopsis gynoecium is a complex structure composed of different tissues. Development is regulated by hormone interactions, especially auxin and cytokinin, as well as the spatiotemporal action of transcription factors and chromatin dynamics, including epigenetic modifications of core histones. SPT is bHLH transcription factor involved in gynoecium development, specifically affecting both auxin and cytokinin responses. GCN5 is a histone acetyltransferase with pleiotropic biological roles including auxin and cytokinin responses in the gynoecium. CLV1 is a receptor kinase, part of the CLAVATA signaling pathway which suppresses the expression of WUS in apical and floral meristems. Previous work has shown that clv1gcn5 double mutants exhibit a plethora of phenotypes including fasciated meristems and abnormal flowers with increased number of stamen and elongated gynoecia with enlarged apical regions and reduced ovaries. In the double mutants, the stem-cell-promoting transcription factor WUS is ectopically overexpressed in the gynoecia. To elucidate genetic interactions between SPT, CLV1 and GCN5 we created all genetic combination between spt, clv1 and gcn5 mutants. We show here that spt mutations largely suppress the phenotypes of clv1gcn5 gynoecia. The enlarged stigma and style and ovary formation are restored in sptclv1gcn5 plants compared to clv1gcn5 plants. The spt mutation also reverses the WUS ectopic overexpression in clv1gcn5 gynoecia. Interestingly spt gynoecia have also reduced WUS expression compared to wild type. These results suggest that SPT mediates the CLV1-GCN5 synergistic interaction during gynoecium development, potentially acting as a positive regulator of WUS expression in the gynoecium.

The role of SPT as a mediator of CLV1 and GCN5 interaction in gynoecium development in Arabidopsis

Tessellated material systems, meaning self-similar subunits arranged to form surface structures, are found throughout various unrelated taxa as well as over a broad range of sizes. An especially interesting system constitutes the armadillo carapace, a rare example of mammal armor involving hard mineralized elements, so called osteoderms embedded in soft connecting tissue. Previous work focused on the structural integrity and histology of individual osteoderms. However, the larger scale organization of armadillo tilings has never been subjected to a larger scale comparative analysis, although the mechanics (e.g. overall fracture resistance) of a tessellation is linked to the geometrical arrangement of its subunits. In this study we digitally examined osteoderm carapaces from micro-CT scans of twelve armadillo species, representing all major lineages within the armadillo phylogeny, in order to quantitatively compare and describe osteoderm shape as well as arrangement and distribution within the entire carapace. Results show that five- and six-sided osteoderms are tied to positive Gaussian curvature similar to the patches on a soccer ball, where a comparable combination of pentagons and hexagons is used. Furthermore, osteoderm number per surface area of entire carapaces reflects a deep split in armadillo phylogeny, separating the two major groups Dasypodidae and Chlamyphoridae. Additionally, Chlamyphorinae display an outstanding carapace architecture that consists of bands comprising exclusively rectangular osteoderms, potentially related to functional adaptations to a specialized nocturnal and fossorial lifestyle that requires increased mobility compared to other armadillo species, while possibly also leading to a decrease in protective performance of the carapace. Our study reveals a hitherto understudied diversity of carapace structure and function in armadillos, a deeper understanding of which will yield further insight into the evolutionary history of the taxon. 

 Tessellated osteoderm carapaces in extant armadillos 

Basal metabolic rate (BMR) – the rate of energy use needed to perform basic, life-sustaining functions – is a universal measure of metabolic rate allowing for comparisons of energy expenditure between species. Many animals inhabit a vast array of challenging environments, an example being living in confined spaces where oxygen levels are likely to be low. Previously it has been shown that species can exhibit both geno- and phenotypic adaptations in metabolic rate to exploit such unique niches. Living for extended periods of time within an enclosed space – in a burrow, den or crevice – will likely require certain physiological and morphological adaptations, and thus influence the biology of the species that occupy them. In this study we are taking a global look at the mammalian kingdom to understand the relationship between BMR and burrow use (fossoriality) in mammals. In particular, we aimed to determine if there was a trait within BMR associated with fossoriality, versus species which live above ground. We used pre-existing data for mammalian BMR and body mass, and 24-life history traits. To account for variation in body size, residual BMR was used (RBMR), controlling for any phylogenetic trends through a phylogenetic least squares model (PGLS) and an MCMCglmm, to account for inter- and intra-specific variation. Overall, mammalian metabolic rate is dictated primarily by environmental temperature. Only aquatic mammals had a detectable trait in RBMR and there was no significant differences in RBMR of terrestrial, fossorial and subterranean mammals, suggesting that species occupying a subterranean niche do not pay any baseline metabolic costs on account of their burrowing lifestyle. This may possibly explain why certain species can live above ground whilst also occupying an underground shelter at night or during other periods of the day. Aquatic mammals, however, had a significantly higher RBMR to all other groups apart from flying mammals. This significantly high BMR may also be due to the energetically demanding thermoregulatory need to maintaining a constant body temperature in cold water, particularly the Arctic/Antarctic waters that the large aquatic mammals in the study will be visiting seasonally, if not occupying year-round. This study has shown that environmental temperature is an important factor when exploring differences in mammalian BMR. Temperature can be used to predict BMR and therefore strongly infers whether a mammal is physiologically suited to living in a particular place or habitat. Changes to the environmental temperatures that these species are experiencing are likely to have knock on effects and alter population spread and change, as well as persistence of populations in certain areas. This highlights the importance of climate change and the largescale effects that small changes in environmental temperature may have on the diversity and distribution of mammalian species on the planet.

No evidence for a signal in mammalian basal metabolic rate associated with a fossorial lifestyle.

The enlarged brains of homeotherms bring behavioural advantages, but also incur high energy expenditures. The ‘expensive brain’ (EB) hypothesis posits that the energetic costs of the enlarged brain and the resulting increased cognitive abilities (CA) were met by either increased energy turnover or reduced allocation to other expensive organs, such as the gut. We tested the EB hypothesis by analysing correlated responses to selection in an experimental evolution model system, which comprises line types of laboratory mice selected for high or low basal metabolic rate (BMR), maximum (VO2max) metabolic rates and random-bred (unselected) lines. The traits are implicated in the evolution of homeothermy, having been pre-requisites for the encephalization and exceptional CA of mammals, including humans. High-BMR mice had bigger guts, but not brains, than mice of other line types. Yet, they were superior in the cognitive tasks carried out in both reward and avoidance learning contexts and had higher neuronal plasticity (indexed as the long-term potentiation) than their counterparts. Our data indicate that the evolutionary increase of CA in mammals was initially associated with increased BMR and brain plasticity. It was also fuelled by an enlarged gut, which was not traded off for brain size.

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The dynamic role of rabbit masticatory apparatus during feeding

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