Belgium

Numerous animals exhibit remarkable adaptations for dynamically altering skin coloration. For instance, chameleons modify guanine crystal spacing in their cells, flounders regulate skin pigment visibility, and cephalopods utilize complex light-diffusing structures to achieve effective camouflage. While shark skin is often perceived as grey, some species demonstrate diverse coloration and camouflage strategies, including countershading and bioluminescence. Recent reports suggest that great white sharks possess dynamic camouflage, as evidenced by the great white shark&#39;s skin color changes to a lighter hue when exposed to adrenaline, while melanocyte-stimulating hormone (MSH) causes a darker hue. Our study on blue sharks (Prionace glauca) reveals a potential nanostructural mechanism for this via a direct association between shark coloration and their skin&#39;s tooth-like dermal denticles, which are well known for their hydrodynamic properties. We show that each denticle produces highly saturated, non-iridescent color through nanoscale structural interactions within its pulp cavity. Inside denticles, varying spatial interactions between pigment cells and cells packed with complex crystal stacks (likely guanine) mediate the perceived color in different body regions. These cellular associations, however, also offer a palette whereby small changes in tissue architecture can manifest as local color changes. Our optical observations of excised blue shark skin reveal it can transition from blue to green, gold to slate gray in response to external stimuli, such as changes in humidity. This suggests that our identified structural color mechanisms provide a pathway for dynamic camouflage, opening an unexplored window into shark ecological adaptations and novel structural mechanisms for producing mutable colors.

SEB Conference 2025

Color dynamics: Novel structural color mechanisms may mediate camouflage strategies of blue sharks

dynamic camouflage

structural coloration

skin color

blue shark

Numerous animals exhibit remarkable adaptations for dynamically altering skin coloration. For instance, chameleons modify guanine crystal spacing in their cells, flounders regulate skin pigment visibility, and cephalopods utilize complex light-diffusing structures to achieve effective camouflage. While shark skin is often perceived as grey, some species demonstrate diverse coloration and camouflage strategies, including countershading and bioluminescence. Recent reports suggest that great white sharks possess dynamic camouflage, as evidenced by the great white shark's skin color changes to a lighter hue when exposed to adrenaline, while melanocyte-stimulating hormone (MSH) causes a darker hue. Our study on blue sharks (Prionace glauca) reveals a potential nanostructural mechanism for this via a direct association between shark coloration and their skin's tooth-like dermal denticles, which are well known for their hydrodynamic properties. We show that each denticle produces highly saturated, non-iridescent color through nanoscale structural interactions within its pulp cavity. Inside denticles, varying spatial interactions between pigment cells and cells packed with complex crystal stacks (likely guanine) mediate the perceived color in different body regions. These cellular associations, however, also offer a palette whereby small changes in tissue architecture can manifest as local color changes. Our optical observations of excised blue shark skin reveal it can transition from blue to green, gold to slate gray in response to external stimuli, such as changes in humidity. This suggests that our identified structural color mechanisms provide a pathway for dynamic camouflage, opening an unexplored window into shark ecological adaptations and novel structural mechanisms for producing mutable colors.

technical paper

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Pelagic fishes have many adaptations to enable their active lifestyles. Arguably, the rockstars of the pelagic teleosts are the bluefin tunas, as they can attain extremely large body sizes (up to ~700 kg), they can swim at very high speeds, they have large areas of the body served by countercurrent heat exchangers, and they can roam into deep and high-latitude waters that are too cold for other tunas. As such, the cardiovascular and respiratory physiology of bluefin tunas has been assumed to be exceptional compared with other teleosts, although testing this assumption has proved difficult due to the substantial challenges of working with highly pelagic species that spend their lives in open water. This presentation will discuss what is known about the cardiorespiratory physiology of bluefin tunas, with an aim to understand just how awesome these species are in comparison with all the other loser teleosts.

How awesome is the cardiorespiratory system of the rockstars of pelagic teleosts, the bluefin tunas?

Understanding how sharks respond to catch and release (C&R) recreational fisheries is a key challenge for both management and biologging research. Survival rates and recovery periods are highly species- and setting-dependent, yet no study has been conducted in European recreational fisheries, despite their popularity. We present the first example of electronic tagging to assess C&R effects on blue (Prionace glauca), porbeagle (Lamna nasus) and tope (Galeorhinus galeus) sharks in the UK, for which data are lacking.
Electronic tags (n=69) revealed high (94.7 – 96.2%) survival rates in all three species, with one case of mortality in each. Mortalities could not be definitively attributed to one aspect of the capture event, as animals appeared in good health upon release. However, two individuals (a porbeagle and a tope shark) were deeply hooked and released with hooks in place, which may have caused injuries invisible to observers. Depth time-series (10-minute resolution; n=16) were used to infer when sharks had recovered from angling through changepoint analysis of 4 movement metrics. Recovery time varied among species, but in most cases lasted less than a day. Pre-recovery, abnormal behaviour varied between- and within-species, though typically involved depth-holding either mid-water or near the sea floor and lower vertical velocities. 
The results suggest that when C&R fisheries are conducted within current best-practice guidelines, post release survival can be high. The recovery analysis further offers important insight into the short-term behaviour of electronically tagged animals, which needs to be better accounted for in telemetry studies of marine species.

Survival and post-release behaviour of pelagic sharks caught in recreational catch-and-release fisheries - insights from electronic tagging

Human-induced environmental changes are increasingly subjecting organisms to stimuli and stressors beyond their evolutionary adaptations. In aquatic ecosystems, certain life stages are expected to be particularly vulnerable, with embryos identified as highly sensitive to environmental stress. Notably, research across diverse taxa indicates that embryos can hatch prematurely, potentially as an adaptive mechanism in response to external stressors, despite potential drawbacks such as underdeveloped behavioral or physiological traits. Surprisingly, in aquatic environments, little research has explored the frequency, causes, and consequences of premature hatching. In this presentation, we give an overview of the current knowledge on premature hatching in aquatic embryos and examine how this process may be exacerbated by human-driven global change. Specifically, we (1) review hatching mechanisms and factors that trigger premature hatching in both experimental and natural settings; (2) assess the biological and ecological consequences of premature hatching across different levels of organization, from individuals to ecosystems; and (3) identify knowledge gaps and propose directions for future research on the causes and implications of this phenomenon. Our review highlights that aquatic embryos exhibit premature hatching in response to a broad range of abiotic (e.g., temperature, oxygen levels, pollutants, light, pH, salinity) and biotic (e.g., predators, pathogens) stressors. Additionally, we provide evidence that rapid thermal ramping can induce premature hatching in fish. Premature hatching is an intriguing yet underexplored area of research and knowledge of the phenomena may play a role in enhancing the resilience of aquatic communities amid ongoing global environmental change.

Global change and premature hatching of aquatic embryos

The global expansion of intensive aquaculture is exposing aquatic animals to increasing environmental pCO2 , but also alkalinity which is artificially elevated to at least partially restore seawater pH. While CO2 -driven ocean acidification research has revealed negative effects on marine invertebrate physiology and growth, the combined effects of high pCO2  and alkalinity are poorly understood. To address this, we exposed economically important king prawns to five aquaculture relevant pCO2  levels for 6 weeks (1,100-20,000 µatm) all pH adjusted to 7.5 by adding NaHCO3  to reflect common aquaculture practices. We fully characterised haemolymph acid-base parameters and ionic composition (inorganic cation/anions, protein and organic osmolytes) in combination with measures of protein homeostasis. These included hemocyanin oxygen affinity (P50 ) as a measure of protein function, and protein ubiquitination and 20S proteasomal activity, both indicators of protein degradation. Initial results show that rising CO2 /alkalinity causes up to 20 % reductions in haemolymph [Na+ ], [K+ ] and [Cl- ] which were associated with a slight linear decrease in hemocyanin P50.  Ongoing work also suggests that protein degradational activity, which is important for body growth and in maintaining a functional proteome, is impaired by high CO2 /alkalinity. Overall, we show that high CO2  and alkalinity in aquaculture severely alters extracellular ionic composition and modifies the function of a key respiratory protein and the regulation of whole-body protein turnover. These findings give insight into how high CO2  impacts protein homeostasis in marine organisms, highlighting a potential mechanism by which adverse environmental conditions impact physiological function and performance in marine organisms.

High CO2 and alkalinity in aquaculture severely impact haemolymph ionic composition and protein homeostasis in king prawns (Penaeus vannamei)

Sea lamprey are anadromous fishes native to the Atlantic coast of North America and Europe. They are considered invasive in the Laurentian Great Lakes, where landlocked populations have contributed to native fisheries' decline. Sea lamprey spend most of their life cycle as filter-feeding larvae before undergoing a complex metamorphosis into a parasitic blood-feeding juvenile, which migrates to sea or in landlocked populations to lakes where they feed on fish hosts (e.g. salmonids). As parasitic juveniles, sea lamprey can consume as much as 30% of their body mass per day in blood, requiring efficient mechanisms to deal with metabolic wastes (ammonia, urea, and acids) from the host blood and those produced through their catabolism of ingested protein. This study investigated the nitrogenous waste and acid-base regulatory capacity of juvenile sea lamprey after three weeks of parasitizing rainbow trout. Further, we focused on the cellular and molecular mechanisms of post-prandial nitrogenous waste handling and acid-base regulation at the gills and throughout the digestive tract. Our results revealed a partially uncompensated respiratory acidosis, increased nitrogenous waste, and base excretion in feeding lamprey. In the intestine, feeding led to acidification of the anterior and mid-intestinal regions and coincided with more pronounced apical/sub-apical H+ -ATPase staining in the enterocytes. These findings reveal key insights into the regulatory capacity that has allowed sea lamprey to contribute to declines in fish populations in the Great Lakes and provide insights into mechanisms utilized by sanguivores to deal with the challenges of blood-feeding.

Mechanisms of nitrogenous waste and acid-base regulation during parasitism by the juvenile sea lamprey, Petromyzon marinus 

The human heel pad loses some of its shock absorbing properties during ageing. It is unclear whether this results from “wear and tear” or from the physiology of ageing itself. To help answer this question, we have studied the mechanical behaviour of the heel pad in populations reflecting a diversity of locomotor habits, footwear and substrate use: Europeans, Ju|’hoan traditional hunter-gatherers from Namibia, and Indian shod and barefoot volunteers. This work builds on seminal studies from the 1990s by Peter Aerts and collaborators on the mechanical properties of the heel pad.
We have collected ultrasound images of the heel pad at different loads, Shore heel hardness, plantar pressures and impact acceleration during walking, and Digital Image Correlation-based plantar skin deformation. For the European population we have also obtained MRI foot scans for subsequent Finite Element Modelling.
Our preliminary analyses indicate that the heel pad tends to get thicker with ageing and that in vivo deformation is greatest in the macro-chamber. Shore hardness correlates weakly with dynamic heel pad elasticity. Skin thickness and heel pad behaviour differs between the populations studied.

The ageing human heel pad: assessing mechanical behaviour in the lab and in the field.

Animals can sleep variably, with substantial flexibility in sleep duration and distribution, in response to ecological conditions. However, robustly quantifying sleep variation, across individuals and populations, is challenging in small animals such as lizards. Using recently developed miniature loggers, we recorded sleep in 19 wild-caught individuals of the Peninsular rock agama lizard (Psammophilus dorsalis). First, we validated the use of electrooculogram (EOG) as a proxy for sleep in lizards by comparing it to diel variation in arousal response. We then compared three populations each from urban and rural environments, for EOG-derived sleep parameters (sleep duration, and bout frequency, duration, and interval), and behaviourally-measured sleep intensity (latency to arousal). Finally, we simulated a predation attempt that induced acute stress in these individuals and tested for changes in sleep response by population type. Lizards slept mostly at night, with a total sleep time of on average 11.7h, typically in 60 min bouts separated by 8 min of wake state. Sleep characteristics did not differ between urban and rural lizards, though daytime sleep bouts were shorter and more consolidated in urban lizards. Contrary to evidence from mammals, acute stress did not impact sleep, overall or with respect to populations; therefore, a greater diversity of animal taxa must be investigated to determine how sleep varies across populations and in response to ecological stressors. In robustly measuring sleep-wake patterns in small vertebrates at a population level, our study paves the way for quantifying sleep responses over longer time periods, in mesocosms and in the wild.

Urbanization and acute stress do not influence sleep expression in lizards

Fungal pathogens continue to pose substantial threats to global food security, causing some of the most devastating crop diseases worldwide. We present a pioneering investigation into the infection-related development of the rice blast fungus,Magnaporthe oryzae, employing a quantitative mass spectrometry-based phosphoproteomic approach. Our study maps 8,005 phosphosites on 2,062 fungal proteins, providing a detailed landscape of the phosphorylation events that orchestrate plant infection. This reveals a profound re-wiring of phosphorylation-based signalling cascades during fungal infection, shedding light on the dynamic molecular responses elicited byM.oryzae. To unravel the broader significance of these findings, we undertook a comparative analysis of phosphosite conservation across 41 fungal species, revealing phosphorylation signatures linked to plant-associated fungal lifestyles, biotrophic and hemibiotrophic fungal infections. As the Pmk1 MAP kinase is a key orchestrator of plant infection in many plant pathogenic fungi, we then used parallel reaction monitoring to identify Pmk1 MAPK substrates. Our investigation defines 32 putative substrates of Pmk1, revealing a complex network of regulatory interactions. This led to identification of a novel regulator, Vts1, which undergoes Pmk1-dependent phosphorylation and is indispensable for the manifestation of rice blast disease. Vts1 is a SAM domain protein that plays an essential function in appressorium morphogenesis, septin aggregation and re-polarisation. Using an analogue-sensitive Pmk1 mutant, parallel reaction monitoring, and subsequent site-specific mutagenesis, we show that a single Pmk1-dependent phosphorylation event is necessary for its function as a virulence determinant during rice blast disease.

Cracking the code of infection: mapping the phosphorylation network behind infection-related development in rice blast fungusMagnaporthe oryzae

The model systemSilene vulgarisand its relatives from theBehenanthasection provide a unique opportunity to explore the relationship between gynodioecy and mitochondrial (mt) genome structure. Complete mt genome sequences from severalS. vulgarispopulations revealed the highest intraspecific mt genome diversity reported in any angiosperm, characterized by extensive intergenic regions, hundreds of repeats, and multiple subgenomes.
The taxonomic diversity withinBehenanthaoffers an ideal framework for studying the origins and evolution of this extraordinary mt genome variation. This section includes both gynodioecious and hermaphroditic species, such asSilene fabaria, which is closely related toS. vulgarisyet exhibits a profoundly different mitogenome. While similar in size,S. fabariamt genome forms a single circular molecule with only a few large repeats, in contrast to the multipartite structure ofS. vulgaris.
The high mt genome diversity and frequent intramolecular rearrangements also impact essential mt genes. Some genes display variable transcription start sites or lack stop codons in certainS. vulgarisgenotypes. Hundreds of nucleus-encoded proteins regulating organellar gene expression must adapt to this intraspecific mt genome variability in gynodioecious species. The recently publishedS. vulgarisnuclear genome now enables the analysis of neo/subfunctionalization in organellar RNA-binding proteins, particularly pentatricopeptide repeat (PPR) proteins, which are associated with extreme mt genome variation.

The Relationship Between the Reproductive System and Mitochondrial Genome Structure in the Gynodioecious SpeciesSilene vulgarisand Its Relatives

Spectral light quality can regulate both the physiology and development of stomata. The combination of red and blue light promotes stomatal development through phytochrome and cryptochrome responses. In dynamic light responses, red light indirectly regulates stomatal opening by stimulating chloroplasts, while blue light rapidly triggers stomatal opening via phototropin-mediated signal transduction. However, the net effects of these responses on stomatal dynamics, whether through stomatal physiological responses or leaf structural development, has not been well distinguished. In a controlled-environment growth chamber experiment, six treatments with different R:B ratios ranging from 0.45 to 2.06 were combined with a fixed photon flux to study the changes in stomata conductance and anatomical properties during flowering in tomato (Solanum lycopersicum). The results showed that as the R:B ratio increased, the time required to complete stomatal opening and closing both became shorter. Correspondingly, the maximum stomatal conductance decreased with increasing R:B ratio. When the R:B ratio was at the minimum of 0.45, stomatal conductance reach the largest value under saturating light. Anatomical results showed that lower R;B ratio makes stomatal conductance at steady state a larger proportion of the maximum determined by anatomy. The R:B ratio had a significant effect on the linear relationship between anatomical potential stomatal conductance and actual diffusive conductance. The experiment demonstrates that stomatal responses are modulated by adjusting the R:B ratio of light in controlled environments, with a larger proportion of blue light promoting wider stomatal opening via physiological mechanisms, and minimal contribution from anatomical changes.

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How awesome is the cardiorespiratory system of the rockstars of pelagic teleosts, the bluefin tunas?

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