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The high, constant body temperatures of endotherms like birds and mammals are thought to facilitate the specialization of biochemical processes to warm temperatures. However, endotherms experience temperature variation (regional heterothermy) across body regions, even as they tightly regulate core temperature. As nocturnal fliers, small bats incur substantial heat loss from their poorly insulated wings via convection and radiative heat transfer to the night sky. Since rate-related processes in muscle slow at cooler temperatures, temperature effects in the wing muscles may impair flight performance and impact flight energetics. Although the cooling of these muscles during flight has implications for locomotor performance, peripheral cooling is rarely quantified in animals because of the logistical challenge posed by measuring body temperatures at multiple points on the trunk and limbs during active locomotion. In the field, surface temperatures measured through methods such as thermal imaging may not reflect the temperatures of deeper functional tissues, while measurements of core body temperature by subcutaneous or intraperitoneal loggers do not capture temperature variation across the body. Lab-based experiments, in which multiple regions of the body can be instrumented for in-flight measurements, may reduce or control for the environmental thermal heterogeneity that likely plays an important role in determining body temperatures in free-flying bats. Here, we demonstrate that bat wings are substantially cooler than the core, and discuss the challenges and benefits of our combined laboratory and field-based approach to expand our understanding of thermoregulatory strategy in bats during active locomotion.

SEB Conference Prague 2024

Quantifying regional heterothermy in flying bats in the field and laboratory 

bats

flight

thermoregulation

technical paper

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Climate warming is pushing aquaculture species to their physiological limits through elevated temperature pressures impacting feed intake, nutrient use, growth, health, and welfare. Emerging research shows that diet (and dietary supplements) can play a significant role in modulating the stress response and improving thermal tolerance, which is pivotal in aquaculture species as the oceans continue to warm. 5-aminolevulinic acid (5-ALA), is an emerging dietary supplement that is the sole precursor to heme and fundamental for the formation of hemoproteins involved in aerobic energy metabolism (haemoglobin, myoglobin, cytochrome c oxidase) and the antioxidant system (catalase). Using juvenile barramundi as a model species, a feed trial was conducted for 6 weeks utilising 5-ALA supplementation in aquafeeds at 3 inclusion levels (control (0 ppm), 15 ppm, 30 ppm). Water temperature was ramped up from 30°C to 37°C, over 4 weeks to determine the diet effects under chronic thermal stress conditions. Although haemoglobin levels and catalase activities remained similar among treatments, growth rates increased with 5-ALA supplementation. 5-ALA supplementation also increased mitochondrial respiration in Oxidative Phosphorylation (OXP) with substrates supporting Complexes I and II. However, oxygen flux in the Leak (non-phosphorylating) respiration state remained similar, indicating that the Leak/OXP ratio decreased with 5-ALA. Therefore, the capacity and apparent efficiency to synthesise ATP had increases with 5-ALA. Overall, as a dietary supplement 5-ALA holds promise in aquafeeds through increasing mitochondrial efficiency, which may account for the observed increases in growth rates, which can improve production efficiency during periods of environmental stress within the aquaculture industry.

Enhancing mitochondrial efficiency: small dietary changes improve fish growth under chronic thermal stress

Climate warming with associated heat waves presents a concerning challenge for ectotherms such as fishes. During heat waves, the ability to rapidly acclimate can be crucial for survival. However, surprisingly little is known about how different species and life stages vary in their acclimation dynamics, including the change in thermal tolerance through acclimation (i.e. acclimation capacity), the duration needed for the acclimation temperature to significantly alter thermal tolerance (i.e. acclimation response time), or the duration needed to achieve full acclimation (i.e. time to full acclimation). To shed light on this knowledge gap, we studied the acclimation dynamics of three wild-caught fishes (goldsinny wrasse, three-spined stickleback and European flounder) by assessing upper thermal tolerance (CTmax) after different periods of time acclimating to a warmed environment, and measured both CTmax and lower thermal tolerance (CTmin) in juvenile and adult lab-bred zebrafish acclimated to warmed or cooled environments. Thermal tolerance of zebrafish and sticklebacks significantly increased after a three hour exposure to a warm treatment, while this took six and 24 hours in wrasses and flounders, respectively. Goldsinny wrasse had the highest acclimation capacity, and did not reach full acclimation and stabilization of CTmax within the duration of the study. All other species fully acclimated between 4–10 days. Furthermore, juvenile zebrafish showed similar acclimation dynamics to adults for both upper and lower thermal tolerance, but had a higher CTmin for all acclimation durations. Our results demonstrate that acclimation dynamics vary across species, but may be similar between life stages within species. Understanding species-specific thermal plasticity is important for accurately modeling the projected impacts of climate change.

Capacity for rapid thermal acclimation differs between life stage and species in fish

The remarkable mechanical properties of spider silk, especially its extensibility and strength, have long fascinated naturalists and engineers alike. Recent advancements have focused on unravelling the structural hierarchies and biochemical compositions that confer these unique properties, paving the way for biomimetic applications in materials science and engineering. In this scenario, spider capture threads pose a unique challenge, as many spiders produce metastructures, which unknown properties depend on both the mechanical characteristics of the fibres composing them, and their geometrical arrangement.
In this work, we focused on the biomechanics of the capture threads of the Southern house spider (Kukulcania hibernalis) employing a combination of high-resolution tensile testing, microscopic examinations, and theoretical modelling. Our findings reveal the critical role of the hidden lengths provided by a unique hierarchical looped fibre architecture, which enhance the thread’s extensibility. Thanks to the theoretical modelling, we reveal how the outstanding extensibility observed in the capture threads of Kukulcania can be explained independent of the nano-structure of the fibres. Furthermore, our research highlights the potential of spider silk meta-structures as a model system for developing fibre-based materials that mimic biological structures for enhanced mechanical performance.


Extreme elongations of Kukulcania hibernalis threads thanks to looped meta-structures

Gastropods use adhesive locomotion to successfully traverse a range of substrates by adapting the properties of a thin mucus layer. Sample collection methods can disrupt the native mucus structure, so to investigate this system effectively a method for visualising the native deposition of gastropod mucus trails in situ was developed. Optical profilometry and video analysis were utilised to uncover how animal behaviour impacts mucus structure and analysis of the dried trail topography provided insight into mucus alignment and deposition rate.

Our results revealed that dried gastropod trails have a non-uniform deposition profile with ridges visible along both edges of the trail. This phenomenon was independent of specimen size for the slug species Arion vulgaris, Arion flagellus and Limax maximus, but direction and velocity did impact the prominence of the trail ridges. The dried trail topography was the inverse of the convex deposition profile observed in the rehydrated mucus trails of a marine gastropod, indicating a potential difference in mucin deposition or alignment that is independent of the mucus hydration state. When compared to the model slug species, Ariolimax columbianus, the species from this study had thinner dried mucus trails, highlighting potential variations in the cost of adhesive locomotion between species. Our results suggest that mucus deposition rate and animal behaviour have a greater impact on mucus trail topography than species or specimen mass. Moreover, analysis of the dried mucus trails can provide invaluable insight into the relationship between the hydration and mucin costs associated with mucus excretion and adhesive locomotion.

Trail Watch: Investigating Gastropod Mucus Trails using Optical Profilometry

Male tree crickets produce advertisememt calls that are essential for mating success. Perception of this sound involves the capture of sound waves by an eardrum and mechanoreception of vibrations by sensory cells within the ear. To aid the detection of courtship calls present at low levels in noisy environments, tree crickets use active amplification within the ear. However, this sensitive system may be overwhelmed when noise is loud or similar in frequency to the call of interest. In this study, we performed a series of experiments to determine how and whether a tree cricket Oecanthus nigricornis eardrum is able to represent a call of interest in the presence of a simulated chorus of distracting calls at varying sound pressure levels and frequencies. Because anthropogenic noise has also been shown to impact the ability for many animals to acoustically communicate, we also performed experiments with white and pink noise as a distracting signal to simulate noise regimes generated by humans. This work provides insight on the mechanical functioning of cricket ears, and also on how these animals may be affected by different ecological conditions, including those generated by humans.

Tree cricket tympanal mechanics in noisy environments

Plants, like all living organisms are subjected to mechanical forces arising either from their environment or from within their own body. To sense these forces, plants like animals, have developed mechanosensitive (MS) channels.
MS channels identified and partially characterized in plants belong to the MSL (Mechanosensitive channel of Small conductance Like), MCA (Mid1-Complementing Activity), Piezo, OSCA (hyperosmolality-gated calcium-permeable) and TPK (Two-Pore K+) families. AtMSL10 from the model plant Arabidopsis, homologous to E.coli EcMscS, was the first plant channel to be molecularly identified and shown to be mechanoactivated. It is predominantly expressed in aerial organs but also in root tips. AtMSL10 catalyzes large fluxes of anions. Amongst multiple mechanical constraints generated by their environment, plants must cope with recurring mechanical stimulation produced by wind. We show that MSL10 activity is amplified by oscillatory stimulation at frequencies corresponding to wind-driven oscillations. Therefore, AtMSL10 is proposed to represent a molecular component allowing the perception of oscillatory mechanical stimulations by plants. Recently, we have also characterized a rapidly activated calcium MS channel (RMA) in Arabidopsis. We are currently investigating the role of this channel in root mechanosensing.
Finally, we will stress the need to reintegrate plant MS channel in the cellular-context. Indeed, MS channels described with the patch-clamp technique are characterized in the absence of an extracellular matrix. There is a need to map the membrane tension at the cellular scale in order to specifying where, and under which conditions, plant MS channels operate.


Mechanotransduction through force-gated ion channels in plants

The centromere is the chromosome region where the microtubules attach during cell division. In monocentric species, new centromeres can appear during evolution at an ectopic chromosomal location. A new centromere often tends to form near the progenitor centromer, and frequently, the establishment of a new centromere is accompanied by inactivation or loss of function of the old centromere. Initially, newly formed centromeres do not usually contain repeat DNAs but mature gradually through the acquisition and accumulation of repeats. As soon as one or a few repeats invade the novel centromere, their accumulation can be achieved by extended gene conversion during DSB repair. In addition to monocentric eukaryotes, which have a single localized centromere on each chromosome, there are holocentric species, with extended repeat-based or repeat-less centromeres distributed over the entire chromosome length. At least two types of repeat-based holocentromeres exist, one composed of many small repeat-based centromere units (small unit-type), and another one characterized by a few large centromere units (large unit-type). We hypothesize that the transposable element-mediated dispersal of hundreds of short satellite arrays and DNA repair formed the small centromere unit-type holocentromere in e.g. Rhynchospora pubera. The large centromere unit-type of the e.g. plant Chionographis japonica is likely a product of simultaneous DNA double-strand breaks and DNA repair, which initiated the de novo formation of repeat-based holocentromeres via insertion of satellite DNA, derived from extra-chromosomal circular DNAs (eccDNAs).

Centromere diversity - Does DNA repair drive the evolution of repeat-based holocentromeres?

Acute monocytic leukaemia (AML-M5) is a bone marrow disease that affects young children. Astonishingly, the discovery of disease-specific induced pluripotent stem cells (iPSCs) capable of recapitulating human pathogenesis allows us to model this disease in vitro. We had previously generated AML-M5-specific-iPSC (AML-M5-iPSCs) from THP-1 cells obtained from a patient[1]. These AML-M5-iPSCs were then induced with growth supplements to enter haematopoietic differentiation to generate monocytic cells. We noticed that reprogramming transgenes Oct3/4, Sox2 and c-Myc were unintentionally integrated into the genome of AML-M5-iPSC during reprogramming. Out of scientific interest, the effects of transgene integration on drug responses were investigated. Firstly, the monocytic cells were characterised to determine their morphological and phagocytotic properties, and compared with their parental cell line THP-1 across 5-, 10-, 15-, 20- and 25-day post-differentiation. Subsequently, cytotoxic effect of Doxorubicin at 0.5, 1, 2 and 4μM on both cells were investigated with CCK-SK viability assay, and apoptotic effect investigated with cell cycle analysis. 
Our results revealed that in terms of size and morphology, both THP-1 and differentiated monocytic cells remained comparable up to 25 days post-differentiation. Within the same duration, their phagocytotic rates also exhibited no significant differences (p>0.05) when investigated with carboxylate-modified red fluorescent latex beads. However, after 24h Doxorubicin treatment, the IC50 value determined for THP-1 cells was 0.59µM, but the IC50 value for differentiated monocytic cells could not be determined; suggesting that they were significantly (p<0.05) less responsive to Doxorubicin. Upon similar treatment conditions, 92.5±3.9% of THP-1 cells entered late apoptosis stage. However, for differentiated monocytic cells, only 0.3±0.2% entered late apoptosis stage, 37.2±1.5% entered necrosis stage and 62.5±1.6% remained in viable stage. Our results showed that transgenes integration was causing monocytic cells to be resistant to Doxorubicin despite the fact the they should only affect haematopoietic differentiation. In addition, the apoptotic effect of Doxorubicin had also been switched to necrotic effect. More interesting, transgene integration did not seem to alter the morphology and phagocytosis of monocytic cells. We postulate that transgenes Oct3/4, Sox2 and c-Myc interfered with the intercalation of Doxorubicin into the DNA, subsequently altering downstream pathways thereby disrupting cell death via apoptosis. In conclusion, further investigations are warranted to determine the mechanism of reprogramming transgene-induced drug resistance in monocytic cells derived from AML-M5-iPSC.


Integration of reprogramming transgenes into AML-M5-iPSC caused differentiated monocytic cells to be resistant to Doxorubicin

Cold stress is one of the major abiotic stress factors affecting rice growth and development, leading to significant yield loss in the context of global climate change. Exploring natural variants that confer cold resistance and the underlying molecular mechanism responsible for this is the major strategy to breed cold tolerant rice varieties. Here, we show that the natural variations of a SIMILAR to RCD ONE (SRO) gene, OsSRO1c, confer cold tolerance in rice at both seedling and booting stages. OsSRO1c possesses intrinsic liquid-liquid phase separation ability in vivo and in vitro and recruits an AP2/ERF transcription factor and cold stress positive regulator, OsDREB2B, into its biomolecular condensates in the nucleus, resulting in elevated transcriptional activity of OsDREB2B. The OsSRO1c-OsDREB2B complex directly senses low temperature through dynamic phase transitions and regulates key cold response genes, including COLD1. Furthermore, introgression of an elite haplotype of OsSRO1c into a cold susceptible indica rice significantly increases its cold resistance ability. Thus, our work reveals a novel cold stress sensing module and provides a promising gene resource for breeding cold tolerant rice varieties.

The OsSRO1c-OsDREB2B complex senses low temperature to confer cold tolerance via direct regulation of COLD1 in rice

Human cultivation during plant domestication imposed strong selection
on fitness relevant traits. The relationship between apparent trait
changes and fitness is not always obvious. For instance, seed color
changed in numerous crops early during their domestication. In the
pseudocereal grain amaranth seed color changed from dark to white
three times during its repeated domestication. However, the genetic
basis and functional relevance of the seed color change is still
unknown.
To study the ecological function of seed pigments in grain amaranth,
we assessed germination properties in hundreds of lines using a
semi-automated phenotyping system and found that white seeds germinate
significantly faster than dark seeds. The metabolomic analysis of
seeds showed reduced accumulation of flavonoids, including the dark
proanthocyanidins, in white seeds. To study the genetic control of the
change, we employed genome-wide association mapping and RNA sequencing
in diverse accessions. Differential gene expression analysis revealed
the downregulation of almost all flavonoid pathway genes in white
seeds. The genomic analyses identified the insertion of a transposable
element (TE) into a regulator of the flavonoid pigment pathway as one
causal mutation for the seed color change. Using full-length
transcript sequencing, we show how the TE induces alternative splicing
in the regulator which results in loss of function for pigment pathway
regulation. We demonstrate how a seemingly fitness-unrelated trait
like seed color can confer environmental adaptation and how the
insertion of a transposable element altered the expression of a whole
metabolic pathway to enable the trait change.

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Quantifying regional heterothermy in flying bats in the field and laboratory

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Enhancing mitochondrial efficiency: small dietary changes improve fish growth under chronic thermal stress

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