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Spiders spin silk into different products, such as fibres, threads and sheets, tailored for specific
functionalities and to fulfil a variety of ecological roles. Examples include draglines and bridging
lines for structural support, as well as webs and sticky threads for prey capture. Most silk products
are made of a combination of different silk fibres with contrasting material properties. The most
common silk types are minor ampullate, major ampullate and aciniform gland silk. Spider silks
exhibit characteristic mechanical properties, including extensibility and tensile strength. How these
properties vary between spider species, gland origins and thread structures as poorly understood.
This study aimed to compare the mechanical properties of different silk products in Pholcidae, with
a particular focus on the cosmopolitan cellar spider (Pholcus phalangioides). P. phalangioides
constructs irregular three-dimensional webs comprising of unique mechanically interesting silk
products. This include capture threads called ‘gumfoots’ which are vertical sticky prey traps
designed to undergo spontaneous deformation and utilizes ‘draglines’ and airborne ‘bridging lines’
which serves for in locomotion and display distinct tensile strength and toughness to hold spider’s
weight. Each of these silk structures were hypothesized to show specific mechanical adaptations.
Preliminary results of tensile test show a significant variety in mechanical properties across
different silk types with varying extensibility, tensile strength and toughness. Further study will
focus on interspecific variation of the structural and mechanical properties of silk products
between pholcid species with different ecology and silk compositions and the composition of fibres
in Pholcidae.

SEB Conference Prague 2024

Comparative Analysis of the Mechanical Properties of Silk Products in Pholcidae

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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.

Because granivorous birds need to exert bite forces to open seeds, evolution resulted in greater bite forces in species feeding on hard seeds. However, beaks also play a role in sound modulation during singing. They are especially important in song fragments with a high trill rate, which require fast open-close movements of the beak. Studies in canaries showed that females prefer songs with high trill rates, implying an important sexual selection pressure on beak speed in this species. In canaries, beak velocities and frequencies are approximately equal during feeding and singing. However, in finches with strong bite forces, like many Darwin’s finches, beak movements during singing are considerably slower than in canaries. Yet, there is no information about the difference in beak velocities and frequencies between feeding and singing in finches with strong beaks. Here we test the hypothesis that, also in species with a strong bite force, song performance is limited by the beak’s movement capacities. This is done using high-speed video recordings of the Java finch (Lonchura oryzivora) during both singing and feeding on seeds. Contrary to our hypothesis, significantly lower beak frequencies occurred during singing compared to during feeding. Although the beak generally rotates at higher amplitudes during singing, our results nevertheless indicate that Java finches are not producing their potential maximum trill rate. Such usage of the beak below its biomechanical potential in terms of speed and frequency during singing suggests different sexual selection pressures compared to species with considerably higher trill rates like canaries.

Need for speed: are beak speed and frequency similar during singing versus feeding in a strong-biting songbird?

Feeding ecology of carnivorous mammals is highly diverse. It is generally accepted, however, that most primarily employ one of three hunting strategies: pursuit predation, pounce/pursuit predation or ambush predation. Knowledge of how morphology and hunting type relate to each other is imperative for our understanding of the feeding ecology of extinct carnivores. 
Here, we offer a first insight into the relationship between trabecular structure in the distal humerus of carnivorous mammals and their respective hunting types. We analyse μCT-scans with the aim of uncovering morphological correlates to behavioural strategies. Our findings are then compared to results for the extinct thylacine (Thylacinus cynocephalus) to infer its likely hunting behaviour.
Results suggest habitual loading of the distal humerus related to hunting type. Higher values in degree of anisotropy (DA) are uncovered for ambush predators and lower values for pounce/pursuit and pursuit predators respectively. DA remains largely unaffected by phylogeny and body mass, pointing to a functional signal. 
Employing our methodology to the extinct thylacine reveals an overlap with extant pounce/pursuit predators, suggesting a pouncing behaviour.


Trabecular structure of the distal humerus in carnivorous mammals

Muscle is the prime mover of animal locomotion, but muscle force is not usually equal to output force. Instead, the instantaneous ratio between output and input force (the mechanical advantage, MA) is modulated by intervening skeletal elements. Traditional functional analysis, focussing on the instantaneous action of gearing, suggests that smaller MA favours speed, while larger MA favours force. However, mounting evidence suggests that this perspective is too simplistic when considering the outcome of a dynamic muscle contraction. We approach this problem systematically by introducing an analytical framework to study the effect of gearing. This framework reveals two mechanisms by which the output speed of a contraction is affected by gearing. First, gearing can limit muscle work output, because it is bound not only by muscle displacement, but also by muscle shortening velocity. Second, it controls how each unit of muscle work is partitioned into system energies (e.g. kinetic energy vs heat). Consequently, smaller gear ratios do not always result in larger output speeds. No single optimal gear ratio exists for any organism, but rather the optimum depends on internal muscle properties and contraction dynamics, as well as external forces. The analytical framework we propose provides a blueprint to determine optimality conditions across muscle physiology, anatomy, mechanical environment and size, and so to investigate form-function relationships in musculoskeletal gearing.

Musculoskeletal gearing for maximum speed: analytic optimization across mechanical environment and size.

Silicon (Si) is increasingly being recognised as an essential element for plant health to tackle abiotic stresses, and it may also deter herbivores from plant-feeding, as a result of tooth wear caused by silica phytoliths. However, direct quantitative evidence for Si-induced wear is scarce. In this study, we subjected pristine Atta vollenweideri ant mandibles to multiple wear treatments on Hordeum vulgare barley leaves, grown with either 0-, 2- or 4-mM Si-supplemented hydroponic media, resulting in varying Si concentrations in the leaves. Pristine mandibles were collected from freshly eclosed ants that had never engaged in foraging, and wear treatments were conducted by driving isolated mandibles through leaf lamina at a constant speed using custom-built clamps attached to a motor stage. To quantify the effects of mandible wear, before, in between, and after each treatment, the forces required to cut standardised PDMS sheets were measured using a custom-built fibre optic force transducer; after 300 mm barley cut length, the cutting forces on PDMS increased significantly across all Si conditions; this force increase, however, was not consistent across Si concentrations, such that the change in cutting force per leaf length cut was 174% larger on 4 mM compared to 0 mM leaves. These results indicate that mandible abrasion may be facilitated by the mechanical contact between cutting edge and silica phytoliths. As increased mandible wear is likely of significant detriment to lifetime foraging efficiency, targeted Si-supplementation may be an effective yet ‘green’ agricultural strategy to provide protection against insect herbivores.

Abrasive silica phytoliths significantly increase mandible wear in leaf-cutter ants

Birds fly within a moving atmosphere, but possess inertia relative to the Earth. As a bird is subjected to changes in the wind, its inertia acts as an anchor, holding it in place while the air washes past it, accelerating it relative to that air. Such wind variations (gradients), if exploited effectively, thus provide valuable opportunities for kinetic energy gain; a concept known as gradient soaring. Seabirds such as the albatross are famous for utilising this effect, exploiting wind gradients above ocean waves and in the atmospheric boundary layer to fly for thousands of miles with minimal energy expenditure. While gradient soaring has been most widely studied for these predictable and large-scale wind gradients, the same mechanisms permit energy gain from small, local and stochastic temporal variations in the wind. Urban environments in particular provide a rich landscape for atmospheric energy gain, where obstacles such as buildings and trees create complex flows with updrafts, wind shear and turbulence; previous research suggests that birds can almost half their energetic costs by utilising the wind in urban environments. Based on the dynamics of a gull-sized aircraft, flights through urban wind flow models have been simulated within an energy-aware path planning framework to elicit energy-gain manoeuvres and quantify the flight cost savings available. This work seeks both to explain the flight strategies of urban birds and to enhance the energy efficiency of small aerial robots.

Bird-Inspired Energy Gain Manoeuvre Discovery in Structured Urban Airflows

Anthropogenic carbon dioxide emissions have been increasing rapidly in recent years, driving pH and oxygen levels to record low concentrations in the oceans. Eastern boundary upwelling systems such as the California Current experience exacerbated ocean acidification and hypoxia (OAH) due to the physical and chemical properties of the transported deeper waters. Research efforts have significantly increased in recent years to investigate the deleterious effects of climate change on marine species, but have not focused on the impacts of simultaneous environmental stressors. Additionally, few have explored the physiological impacts of these environmental stressors on early life stages, which are more vulnerable and represent natural population bottlenecks in organismal life cycles. The physiological response of the red sea urchin (Mesocentrotus franciscanus) to co-occurring stressors was assessed by exposing larvae to varying OAH conditions observed along the California coast. Graded responses, proportional to treatment severity, indicate that minor shifts in OAH affect morphology and gene expression, especially related to growth and pH homeostasis. In addition to this gradient, breakpoints can be detected, representing drastic shifts in response curves and a potential environmental threshold below which growth and performance are profoundly impacted. The phenotypic and transcriptional breakpoints occurred between DO of 2.64-3.67 mg/L and pH 7.6-7.85 with an additional transcriptional breakpoint between DO 0.88-1.54 mg/L and pH 7.2-7.45. By assessing the physiological response and gene expression of these species, we can inform future management actions to mitigate OAH-related impacts and maintain fishery populations.

Transcriptional and Morphological Response of Red Sea Urchin Larvae (Mesocentrotus franciscanus) to Combined Ocean acidification and Hypoxia

In recent years, Nephrotic Syndrome (NS) has emerged as a significant challenge in global public health. NS encompasses a spectrum of diseases affecting kidney function, with Membranous Glomerulonephritis (MGN) being the most prevalent in mammals.Common indicators of NS include protein loss in urine and decreased blood albumin levels. Primary glomerulonephritis is the leading cause, with Anti-Phospholipase A2 receptor antibodies (anti-PLA2R) serving as a diagnostic marker for MGN, as per Kidney Disease: Improving Global Outcomes (KDIGO) guidelines.
Our study employed various machine learning techniques to develop predictive models using disease classification data and examination results such as complete blood count, blood and urine biochemistry. After data refinement, the dataset was split into training and testing sets, with Python utilized to build machine learning models. Statistical analysis revealed significant differences (p<0.05) in BUN, Creatinine, and eGFR between normal individuals and those predicted to have the disease. The machine learning process incorporated Synthetic Minority Oversampling Technique (SMOTE) to address imbalanced data and 5-Fold Cross-Validation for validation. Final models utilized the Random Forest algorithm and eXtreme Gradient Boosting (XG Boost), achieving an Accuracy and AUC of 0.83, indicating robust predictive performance.
Our methodology, leveraging routine blood and urine tests alongside machine learning algorithms, enables accurate prediction of MGN. In the future, this methodology holds promise for application in mouse research and potentially diagnosing human diseases in clinical.

Predicting Membranous glomerulonephritis in Mammals Using Machine Learning

After prolonged noise exposure, we lose our hearing ability, which is often temporary and typically recovers (resilience). Previously, we established the desert locust, Schistocerca gregaria, as a model for auditory recovery after noise exposure. In this work we wished to track the rate of short-term recovery after noise exposure. In order to do this, we conducted over 600 independent measurements of auditory system function after noise exposure and quantified both the transduction current from individual auditory neurons and spiking responses from the auditory nerve. For the sound-evoked nerve response we find a rapid increase in recovery over the first 8 hours, followed by a more gradual recovery over the next 20 hours. For the transduction current we find a more steady recovery after noise exposure. We wanted to understand the genetic basis of this recovery. Therefore, we extracted RNA from auditory Müller’s organ to identify transcriptomic changes responsible.







Previously, we established the desert locust, Schistocerca gregaria, as a model for auditory robustness and resilience. We found differences in resilience when comparing young and aged locusts. Regardless of age, the sound-evoked auditory nerve response recovers completely in young and aged locusts, however, the sound-evoked transduction current does not recover in aged locusts. We thus identify a potential plastic mechanism that compensates for a noise-induced decrease in transduction current in aged locusts. We then examine the auditory resilience of the locust ear in higher resolution, at the level of both the sound-evoked auditory nerve response and transcriptomic changes over the first 28 hours after noise exposure. We find a rapid increase in recovery over the first 8 hours following noise exposure, followed by a more gradual recovery over the following 20 hours. Our high-resolution transcriptomic results offer insight into the fundamental mechanisms of auditory recovery. 




Tracking the rate of recovery of the locust's auditory system after noise-exposure.

Insects exchange respiratory gases through a gas-filled, highly branched tracheal system, that extends from paired segmental sipracles to fine tracheoles. Gas exchange between the tracheoles and the tissues is entirely diffusive, but locusts, and many other insects, rely on convection of gas within the tracheal system for facilitating gas transport from the environment to the tracheoles even at rest. In this study we compared structural and functional tracheal system traits between migratory locust (Locusta migratoria) populations originating in the Tibetan Plateau (TP; 4000 above sea level) and in low altitude Hainan Province (HP), China. We hypothesized that the TP locusts have adapted to low environmental oxygen availability in their natural habitat. Following multiple generation rearing at sea-level laboratory conditions TP locusts were significantly smaller than HP conspecifics, yet their tracheal volume was significantly higher. Mass-specific metabolic rates were similar in both populations, but gradual exposure to decreasing environmental oxygen levels yielded a more pronounced metabolic (and ventilatory) response in non-adapted HP compared with TP. Critical oxygen partial pressures, under which metabolic rates cannot be maintained, were marginally lower in TP compared with HP (1.8±0.2 and 2.4±0.2 kPa, respectively), but just short of statistical significance (p=0.07). Nevertheless, this evolved variation in respiratory system function may be more pronounced during activity, when tissue oxygen demand is higher. Moreover, exposure to hypoxic conditions throughout development resulted in lower adult body mass in HP, but not TP locusts, compared with development in normoxia, highlighting long-term effects of evolved respiratory adaptation.

Respiratory adaptation to high altitude in migratory locusts

The Asia-Pacific aquaculture, renowned for its success, faces mounting climate change
challenges. Intensified heatwaves and erratic weather disrupt operations, with summer
temperature extremes breaching optimal thresholds. This leads to a proliferation of pathogenic
microorganisms and harmful substances, jeopardizing the industry's sustainability and output.
Resveratrol (RSV), a natural polyphenolic compound, is well-known for its antioxidant properties
and modulates inflammatory responses against pathogens. Our study aims to assess the efficacy
of RSV-supplemented diets in combating bacterial infections and mitigating inflammation in
aquaculture species during summer conditions.
Our study uses tropical tilapia (Oreochromis mossambicus) to examine the impact of RSVsupplemented
diets on gut microbial composition. PacBio 16s rRNA sequencing unveiled a
decrease in potentially pathogenic bacteria (Aeromonas) and enhanced in beneficial probiotics
(Cetobacterium) in both the gut and gills of tilapia fed with RSV. Moreover, in vitro investigations
demonstrated that RSV inhibits Aeromonas growth. Further analysis using RNA-Seq to investigate
the microbial composition changes induced by RSV. We found that RSV as a dietary supplement
can reduce the expression levels of immune response-related genes (RAGE, IL-1β, IL-6, cox2).
Overall, our findings suggest that RSV supplementation holds potential as a promising
dietary supplement for tropical fish, aiding their resilience against the adverse effects of summer
temperature spikes induced by climate change and contributing to the sustainability and
productivity of the aquaculture industry.

Comparative Analysis of the Mechanical Properties of Silk Products in Pholcidae

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Need for speed: are beak speed and frequency similar during singing versus feeding in a strong-biting songbird?

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