Publications

Vertebrate skin appendages are diverse micro-organs such as scales, feathers, and hair. These units typically develop from placodes, whose spatial patterning involves conserved chemical reaction-diffusion dynamics. Crocodile head scales are a spectacular exception to this paradigm, as they instead arise from a mechanically dominated process of compressive folding driven by constrained skin growth. Here, we reveal that chemical versus mechanical processes pattern tortoise scales in different regions of their head. Indeed, we show that placode-derived scales emerge across the peripheral head surfaces while remaining absent from the central dorsal region where scales subsequently form through a mechanical folding process. Using light sheet microscopy, we build a three-dimensional mechanical model that qualitatively recapitulates the diversity of scale patterns observed in this central head region in different tortoise species. Overall, our analyses indicate that mechanical head-scale patterning likely arose before the divergence between Testudinata and Archosauria, and was subsequently lost in birds.

Blood vessels expand and contract actively as they continuously experience dynamic external stresses from blood flow. The mechanical response of the vessel wall is that of a composite material: its mechanical properties depend on its cellular components, which change dynamically as the cells respond to external stress. Mapping the relationship between these underlying cellular processes and emergent tissue mechanics is an ongoing challenge, particularly in endothelial cells. Here we assess the mechanics and cellular dynamics of an endothelial tube using a microstretcher that mimics the native environment of blood vessels. The characterization of the instantaneous monolayer elasticity reveals a strain-stiffening, actin-dependent and substrate-responsive behaviour. After a physiological pressure increase, the tissue displays a fluid-like expansion, with the reorientation of cell shape and actin fibres. We introduce a mechanical model that considers the actin fibres as a network in the nematic phase and couples their dynamics with active and elastic fibre tension. The model accurately describes the response to the pressure of endothelial tubes.

Monothalamous (single-chambered) foraminifera are widespread in marine benthic environments and are also a common part of freshwater and soil microbial communities. Based on molecular and morphological characteristics, seven non-marine families are currently recognized, branching either as sisters to marine clades or independently within the paraphyletic class Monothalamida. In this study, we describe a new monothalamous freshwater foraminifera sampled from a Pyrenean pond near the French town of Cauterets. We erect the novel genus Poseidonella, with its type species Poseidonella transaquatica sp. nov. The new species branches within the marine clade E, which includes the genera Psammophaga, Vellaria, Niveus, and Nellya. This represents the first evidence of a mixed clade comprising both marine and freshwater monothalamids, highlighting an ongoing transition from coastal marine environments to freshwater habitats.

The discovery in 1938 of a living coelacanth, Latimeria chalumnae, triggered much research and discussion on the evolutionary history and phylogeny of these peculiar sarcopterygian fishes. Indeed, coelacanths were thought to represent the 'missing link' between fishes and tetrapods, a phylogenetic position which is now dismissed. Since the first analyses using a phylogenetic approach were carried out three decades ago, a relatively similar data matrix has been consistently used by researchers for running analyses, with no significant changes aside from the addition of new taxa and characters, and minor corrections to the states' definition and scorings. Here, we investigate the phylogeny of Actinistia with an updated data matrix based on a list of partially new or modified characters. From the initial list of characters available in the most recent studies, we removed 16 characters, modified 16 other characters' definition and added 18 new characters, resulting in a list of 112 characters. We also revised the data matrix by correcting 171 miscoding found for 37 taxa. Based on the new phylogeny, we propose a new classification of coelacanths including 46 coelacanth genera, part of them allocated within nine families and four sub-families. Most of these groups were already named but were not recognised as clades, or poorly or not diagnosed in previous phylogenetic analyses. We provide several new or emended diagnoses for each clade. For the first time, a set of Palaeozoic coelacanth genera are found gathered within a clade, namely the Diplocercidae. All Mesozoic coelacanths, including extant Latimeria, are resolved as members of the order Coelacanthiformes, a clade that arose in the Permian, with Coelacanthus diverging first. We also found that most Mesozoic coelacanths are gathered into a clade, the Latimerioidei, itself divided into the Latimeriidae and the Mawsoniidae, each of which is divided into two subfamilies. Although these important changes, the new phylogeny of the Actinistia shows no significant alteration, and it remains relatively similar compared to previous studies. This demonstrates that the coelacanth phylogeny is now rather stable despite the weak support for most nodes in the phylogeny, and despite the difficulty of defining relevant morphological characters to score in this relatively slowly evolving lineage.

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Small leisure boat harbours have important aesthetic and recreational values in any country with a coastline. In Sweden, there are about 860 000 leisure boats, which is one of the world's highest numbers in relation to the country's population. However, small boat harbours also present a wide range of environmental problems, including the introduction of alien species and high pollution. In this study, we investigated the ecological quality status (EcoQS) of the Hinsholmskilen small boat harbour, located southwest of the city of Gothenburg (Sweden). We performed a reconnaissance survey of the harbour's previously unstudied benthic foraminiferal communities and analysed surface sediment (0–2 cm) samples for potentially toxic elements: copper (Cu), zinc (Zn), lead (Pb), cobalt (Co), nickel (Ni), chromium (Cr), mercury (Hg), and arsenic (As). The results show that, based on the total benthic foraminiferal distribution (dead and live specimens), the assemblages in Hinsholmskilen harbour represent a typical European estuarine community with highly abundant Ammonia and Elphidium species. Based on molecular and morphological data, we report the presence of two alien and putatively invasive species likely originating from Asia: Trochammina hadai and Ammonia confertitesta (phylotype T6). Both species have recently been identified elsewhere on the Swedish west coast based on molecular and morphological data but do not have a well-known distribution. The sediment analysis for potentially toxic elements showed that the harbour has good to high EcoQS corresponding to no or little deviation from reference conditions for Cd, Co, Ni, and Pb distribution. Some of the contaminants (Pb, As, Zn, and Cr) showed poor to bad EcoQS in the innermost harbour in proximity to high-pressure cleaning plants, where boats are usually lifted, cleaned, and prepared for winter storage on land. Finally, Cu and Hg showed consistently bad and poor EcoQS all over the harbour, reflecting the use of both metals as biocides in antifouling boat paints.

The role of circadian clocks in regulating metabolic processes is well known; however, their impact on metabolic states across species and life stages remains largely unexplored. This study investigates the relationship between circadian rhythms and metabolic regulation in the Drosophila larval fat body, a metabolic hub analogous to the mammalian liver and adipose tissue. Surprisingly, the fat body of period null mutants, which lack a functional circadian clock in all tissues, exhibited 12-hour rhythms in gene expression, particularly those involved in peroxisome function, lipid metabolism, and oxidative stress response. These transcriptomic rhythms were aligned with 12-hour oscillations in peroxisome biogenesis and activity, reactive oxygen species levels, and lipid peroxidation. Furthermore, period mutants exhibited 12-hour rhythms in body fat storage, ultimately leading to a net reduction in body fat levels. Collectively, our results identify clock-independent ultradian rhythms in lipid metabolism that are essential for larval survival and development.

Large numbers of spherical, organic-walled, monothalamous foraminifera were observed and isolated from the fine-sized sediment fraction collected at hadal depths in the Aleutian trench. The foraminifer was one of the few living species found among diatom frustules that make up most of this sediment fraction. Morphologically, the species resembles the genus Bathyallogromia described from the Weddell Sea and subsequently found in the abyssal Arctic Ocean, and other high latitude areas but never in such massive abundance. Molecular phylogenetic analyses based on partial 18S rRNA gene sequences confirmed its generic identification as a new species within the Bathyallogromia clade that is described here as Bathyallogromia brandtae sp.nov. Our study offers new evidence that deep-sea monothalamous foraminifera can proliferate in extreme hadal settings and have biogeographic distributions that are more restricted than is commonly assumed.

Neorotalia leeuwinensis n. sp. is morphologically and genetically distinct from other calcarinids that are present in very shallow waters along the western margin of Australia and has not been recognised amongst known species elsewhere. The distributions of calcarinids along the margin has been surveyed from 22 sites. Four distinct latitudinally-based regions are defined related to temperature. Neorotalia leeuwinensis n. sp. has a known latitudinal range of 30°S to 34°S (>19°C, 30-year average winter minimum sea temperature in the north and >18°C in the south). The main microhabitat observed for the species is the articulate coralline algae Amphiroa gracilis, which usually lives among a diversity of macrophytes in very shallow high-energy environments on the rock platforms. Test shape, robust peripheral spines, and pore tubes are related to the high-energy epibiont lifestyle on the algal branches. Significant marine and terrestrial climatic gradients along the west coastline of Australia from the tropics to the south apparently control calcarinid species distributions, but the reasons for endemism require much more study of environmental parameters and molecular analyses of species.

Blood vessels expand and contract actively as they continuously experience dynamic external stresses from blood flow. The mechanical response of the vessel wall is that of a composite material: its mechanical properties depend on its cellular components, which change dynamically as the cells respond to external stress. Mapping the relationship between these underlying cellular processes and emergent tissue mechanics is an ongoing challenge, particularly in endothelial cells. Here we assess the mechanics and cellular dynamics of an endothelial tube using a microstretcher that mimics the native environment of blood vessels. The characterization of the instantaneous monolayer elasticity reveals a strain-stiffening, actin-dependent and substrate-responsive behaviour. After a physiological pressure increase, the tissue displays a fluid-like expansion, with the reorientation of cell shape and actin fibres. We introduce a mechanical model that considers the actin fibres as a network in the nematic phase and couples their dynamics with active and elastic fibre tension. The model accurately describes the response to the pressure of endothelial tubes.