La flore vasculaire de l’île de Cavallo (archipel des Lavezzi, Corse) : diversité, intérêt biogéographique et conservation

This study provides the first detailed assessment of the vascular flora of the Cavallo Island and its three satellite islands or islets (Corsica, Bouchesde-Bonifacio). It is the Corsican island which has the highest floristic richness with 440 taxa (species and subspecies), all inventories combined. The current flora (i. e. occurring after 1990) includes 426 taxa, of which 371 indigenous and 55 exotic plants, introduced voluntarily or not by man. Of this total, 155 taxa (109 indigenous and 46 exotics) were never been reported on the Lavezzi archipelago. This high floristic richness, compared to other west-Mediterranean islands of similar size, is explained by the area of Cavallo island, the largest of the peri-corsican islands, and to the diversity of environments, including the presence of a permanent lake, the Greco lake. Cavallo Island and its islets contain 70 plant species of importance (i. e. endemic, rare, protected or threatened), eight of which were not currently inventoried. These surveys performed in 2013–2015 highlight the presence of some very rare plants in Corsica (Anacamptis morio subsp. longicornu, Callitriche brutia, Limonium bonifaciense, Limonium strictissimum) and infrequent endemics (Acis rosea, Bryonia marmorata, Crocus minimus, Serapias nurrica, Silene velutina) that were not known to the island. The strong human impact explains the presence of 55 introduced taxa and at least subspontaneous in the «natural environment», of which 50 had not yet been reported on the island. The results of this study are discussed in terms of (1) specific richness compared to other western Mediterranean islands of similar surface, (2) functional diversity (analysis of demographic strategies of Grime), (3) biogeographic originality and conservation issues in order to better preserve in the future this exceptional floristic heritage but for too long unrecognized.Cette étude dresse le premier bilan détaillé de la flore vasculaire de l’île Cavallo et de ses trois îles ou îlots annexes (Corse, Bouches-de-Bonifacio). Il s’agit de l’île satellite corse qui comporte la plus forte richesse floristique avec 440 taxons (espèces et sous-espèces) signalés, tous inventaires confondus. La flore actuelle (présence postérieure à 1990) s’élève à 426 taxons, dont 371 indigènes et 55 exotiques introduits volontairement ou non par l’homme. Parmi ce total, 155 taxons (109 indigènes et 46 exotiques) n’avaient jamais encore été signalés sur l’archipel des Lavezzi. Cette forte richesse floristique, comparée à celle d’autres îles ouest-méditerranéennes de taille voisine, est liée à la superficie de Cavallo, la plus vaste des îles péri-corses, et à la diversité des milieux dont la présence d’un plan d’eau permanent, l’étang du Greco. L’île Cavallo et ses îlots comportent 70 végétaux «patrimoniaux» (endémiques, rares, protégés ou menacés) dont 8 non revus actuellement. Les inventaires de 2013-2015 mettent notamment en évidence la présence de certains végétaux très rares en Corse (Anacamptis morio subsp., longicornu, Callitriche brutia, Limonium bonifaciense, Limonium strictissimum) et d’endémiques peu fréquents (Acis rosea, Bryonia marmorata, Crocus minimus, Serapias nurrica, Silene velutina) qui n’étaient pas connus de l’île. Les impacts anthropiques forts expliquent la présence de 55 taxons introduits et au moins subspontanés dans le «milieu naturel», dont 50 n’avaient pas été encore signalés sur l’île. Les résultats de cette étude sont discutés en terme (1) de richesse spécifique par rapport à des îles ouest-méditerranéennes de surfaces voisines, (2) de diversité fonctionnelle (analyse des stratégies démographiques de Grime), (3) d’originalité biogéographique et d’enjeux de conservation afin de mieux préserver à l’avenir ce patrimoine floristique exceptionnel mais resté trop longtemps méconnu.Médail Frédéric, Petit Yohan, Delage Alain, Paradis Guilhan, Hugot Laetitia. La flore vasculaire de l’île de Cavallo (archipel des Lavezzi, Corse) : diversité, intérêt biogéographique et conservation. In: Ecologia mediterranea, tome 43 n°2, 2017. Le patrimoine naturel de l'île de Cavallo (archipel des Lavezzi, Corse) : écologie, biogéographie et conservation. pp. 103-158

Calcium- and Otoferlin-Dependent Exocytosis by Immature Outer Hair Cells

International audienceImmature cochlear outer hair cells (OHCs) make transient synaptic contacts (ribbon synapses) with type I afferent nerve fibers, but direct evidence of synaptic vesicle exocytosis is still missing. We thus investigated calcium-dependent exocytosis in murine OHCs at postnatal day 2 (P2)–P3, a developmental stage when calcium current maximum amplitude was the highest. By using time-resolved patch-clamp capacitance measurements, we show that voltage step activation of L-type calcium channels triggers fast membrane capacitance increase. Capacitance increase displayed two kinetic components, which are likely to reflect two functionally distinct pools of synaptic vesicles, a readily releasable pool (RRP; τ = 79 ms) and a slowly releasable pool (τ = 870 ms). The RRP size and maximal release rate were estimated at ∼1200 vesicles and ∼15,000 vesicles/s, respectively. In addition, we found a linear relationship between capacitance increase and calcium influx, like in mature inner hair cells (IHCs). These results give strong support to the existence of efficient calcium-dependent neurotransmitter release in immature OHCs. Moreover, we show that immature OHCs, just like immature IHCs, are able to produce regenerative calcium-dependent action potentials that could trigger synaptic exocytosis in vivo . Finally, the evoked membrane capacitance increases were abolished in P2–P3 OHCs from mutant Otof −/− mice defective for otoferlin, despite normal calcium currents. We conclude that otoferlin, the putative major calcium sensor at IHC ribbon synapses, is essential to synaptic exocytosis in immature OHCs too

Ionomics suggests niche differences between sympatric heathers (Ericaceae)

International audienceBackground and aims: The co-existence of large number of competing plant species with the same basic needs is a major question in ecology, particularly when this involves closely related species. Methods: We investigated the ecology of six heather species (Calluna vulgaris & Erica spp., Ericaceae) able to cohabit in the same heathlands. We characterised the ionome, i.e. the mineral composition of the plants using a sampling strategy specifically designed to control for soil effects. Nine plant communities in Limousin, France, were investigated, representing eight combinations of different species, on serpentine and non-serpentine substrates. Results: Ionome was influenced by both taxonomic and environmental factors with significant interactions between them. We found that species growing in sympatry had distinct ionomic profiles, i.e. they differ in their leaf mineral content, suggesting different nutritional strategies. Different mycorrhizal associations may be hypothesised to explain these different chemical signatures. Conclusions: Differential use of the soil nutrients could explain the co-existence of closely related species. It may also explain the diversity of certain shrubby ecosystems or large shrubby genera such as Erica. Ionomics is therefore a promising tool for ecological studies in non-model organisms

VeriTracer: Context-enriched tracer for floating-point arithmetic analysis

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Comparative analysis of the alien vascular flora of Sardinia and Corsica

This article provides a comparison of the vascular alien flora of Sardinia (Italy) and that of Corsica (France), both territories belonging to the Western Mediterranean biogeographic subregion. The study has recorded 598 (90 doubtful) alien taxa in Sardinia (18% of the total flora) while 553 (87 doubtful) in Corsica (17%); six are new report to Sardinia and 27 to Corsica. A total of 234 taxa are common to both islands. Neophytes are 344 taxa (68% of the total) in Sardinia and 399 taxa (73%) in Corsica. The invasive component includes 64 taxa in Sardinia (13% of the alien flora) and 99 taxa (21%) in Corsica, 33 of them common to both territories. The total 740 alien taxa of Sardinia and Corsica are included in 93 families; being Fabaceae the richest. The comparison of the biological spectrum reveals that phanerophytes (202 taxa, 40%) are the most represented in Sardinia and therophytes (149 taxa, 32%) in Corsica. A study of the geographical origin shows supremacy of the American element in Sardinia (170 taxa, 34%) and in Corsica (136 taxa, 29%). The majority of taxa arrived as a result of intentional human introductions, mainly for ornamental use (247 taxa, 49% in Sardinia; 208 taxa, 45% in Corsica). Seminatural, agricultural and synanthropic are the most occupied habitats. These data show the need for joint action to stem the increasingly worrying phenomenon of the alien flora in order to reduce the negative effects on natural habitats and native flora

Different Ca V 1.3 Channel Isoforms Control Distinct Components of the Synaptic Vesicle Cycle in Auditory Inner Hair Cells

International audienceThe mechanisms orchestrating transient and sustained exocytosis in auditory inner hair cells (IHCs) remain largely unknown. These exocytotic responses are believed to mobilize sequentially a readily releasable pool of vesicles (RRP) underneath the synaptic ribbons and a slowly releasable pool of vesicles (SRP) at farther distance from them. They are both governed by Cav1.3 channels and require otoferlin as Ca2+ sensor, but whether they use the same Cav1.3 isoforms is still unknown. Using whole-cell patch-clamp recordings in posthearing mice, we show that only a proportion (∼25%) of the total Ca2+ current in IHCs displaying fast inactivation and resistance to 20 μm nifedipine, a l-type Ca2+ channel blocker, is sufficient to trigger RRP but not SRP exocytosis. This Ca2+ current is likely conducted by short C-terminal isoforms of Cav1.3 channels, notably Cav1.342A and Cav1.343S, because their mRNA is highly expressed in wild-type IHCs but poorly expressed in Otof-/- IHCs, the latter having Ca2+ currents with considerably reduced inactivation. Nifedipine-resistant RRP exocytosis was poorly affected by 5 mm intracellular EGTA, suggesting that the Cav1.3 short isoforms are closely associated with the release site at the synaptic ribbons. Conversely, our results suggest that Cav1.3 long isoforms, which carry ∼75% of the total IHC Ca2+ current with slow inactivation and confer high sensitivity to nifedipine and to internal EGTA, are essentially involved in recruiting SRP vesicles. Intracellular Ca2+ imaging showed that Cav1.3 long isoforms support a deep intracellular diffusion of Ca2+SIGNIFICANCE STATEMENT Auditory inner hair cells (IHCs) encode sounds into nerve impulses through fast and indefatigable Ca2+-dependent exocytosis at their ribbon synapses. We show that this synaptic process involves long and short C-terminal isoforms of the Cav1.3 Ca2+ channel that differ in the kinetics of their Ca2+-dependent inactivation and their relative sensitivity to the l-type Ca2+ channel blocker nifedipine. The short C-terminal isoforms, having fast inactivation and low sensitivity to nifedipine, mainly control the fast fusion of the readily releasable pool (RRP); that is, they encode the phasic exocytotic component. The long isoforms, with slow inactivation and great sensitivity to nifedipine, mainly regulate the vesicular replenishment of the RRP; that is, the sustained or tonic exocytosis

Control of exocytosis by synaptotagmins and otoferlin in auditory hair cells.

International audienceIn pre-hearing mice, vesicle exocytosis at cochlear inner hair cell (IHC) ribbon synapses is triggered by spontaneous Ca(2+) spikes. At the onset of hearing, IHC exocytosis is then exclusively driven by graded potentials, and is characterized by higher Ca(2+) efficiency and improved synchronization of vesicular release. The molecular players involved in this transition are still unknown. Here we addressed the involvement of synaptotagmins and otoferlin as putative Ca(2+) sensors in IHC exocytosis during postnatal maturation of the cochlea. Using cell capacitance measurements, we showed that Ca(2+)-evoked exocytosis in mouse IHCs switches from an otoferlin-independent to an otoferlin-dependent mechanism at postnatal day 4. During this early exocytotic period, several synaptotagmins (Syts), including Syt1, Syt2 and Syt7, were detected in IHCs. The exocytotic response as well as the release of the readily releasable vesicle pool (RRP) was, however, unchanged in newborn mutant mice lacking Syt1, Syt2 or Syt7 (Syt1(-/-), Syt2(-/-) and Syt7(-/-) mice). We only found a defect in RRP recovery in Syt1(-/-) mice which was apparent as a strongly reduced response to repetitive stimulations. In post-hearing Syt2(-/-) and Syt7(-/-) mutant mice, IHC synaptic exocytosis was unaffected. The transient expression of Syt1 and Syt2, which were no longer detected in IHCs after the onset of hearing, indicates that these two most common Ca(2+)-sensors in CNS synapses are not involved in mature IHCs. We suggest that otoferlin underlies highly efficient Ca(2+)-dependent membrane-membrane fusion, a process likely essential to increase the probability and synchrony of vesicle fusion events at the mature IHC ribbon synapse

Viral transfer of mini-otoferlins partially restores the fast component of exocytosis and uncovers ultrafast endocytosis in auditory hair cells of otoferlin knock-out mice

International audienceTransmitter release at auditory inner hair cell (IHC) ribbon synapses involves exocytosis of glutamatergic vesicles during voltage activation of L-type Cav1.3 calcium channels. At these synapses, the fast and indefatigable release of synaptic vesicles by IHCs is controlled by otoferlin, a six-C2-domain (C2-ABCDEF) protein that functions as a high-affinity Ca2+ sensor. The molecular events by which each otoferlin C2 domain contributes to the regulation of the synaptic vesicle cycle in IHCs are still incompletely understood. Here, we investigate their role using a cochlear viral cDNA transfer approach in vivo, where IHCs of mouse lacking otoferlin (Otof-/- mice of both sexes) were virally transduced with cDNAs of various mini-otoferlins. Using patch-clamp recordings and membrane capacitance measurements, we show that the viral transfer of mini-otoferlin containing C2-ACEF, C2-EF, or C2-DEF partially restores the fast exocytotic component in Otof-/- mouse IHCs. The restoration was much less efficient with C2-ACDF, underlining the importance of the C2-EF domain. None of the mini-otoferlins tested restored the sustained component of vesicle release, explaining the absence of hearing recovery. The restoration of the fast exocytotic component in the transduced Otof-/- IHCs was also associated with a recovery of Ca2+ currents with normal amplitude and fast time inactivation, confirming that the C-terminal C2 domains of otoferlin are essential for normal gating of Cav1.3 channels. Finally, the reintroduction of the mini-otoferlins C2-EF, C2-DEF, or C2-ACEF allowed us to uncover and characterize for the first time a dynamin-dependent ultrafast endocytosis in IHCs.SIGNIFICANCE STATEMENT Otoferlin, a large six-C2-domain protein, is essential for synaptic vesicle exocytosis at auditory hair cell ribbon synapses. Here, we show that the viral expression of truncated forms of otoferlin (C2-EF, C2-DEF, and C2-ACEF) can partially rescue the fast and transient release component of exocytosis in mouse hair cells lacking otoferlin, yet cannot sustain exocytosis after long repeated stimulation. Remarkably, these hair cells also display a dynamin-dependent ultrafast endocytosis. Overall, our study uncovers the pleiotropic role of otoferlin in the hair cell synaptic vesicle cycle, notably in triggering both ultrafast exocytosis and endocytosis and recruiting synaptic vesicles to the active zone

Numerical uncertainty in analytical pipelines lead to impactful variability in brain networks

International audienceThe analysis of brain-imaging data requires complex processing pipelines to support findings on brain function or pathologies. Recent work has shown that variability in analytical decisions, small amounts of noise, or computational environments can lead to substantial differences in the results, endangering the trust in conclusions. We explored the instability of results by instrumenting a structural connectome estimation pipeline with Monte Carlo Arithmetic to introduce random noise throughout. We evaluated the reliability of the connectomes, the robustness of their features, and the eventual impact on analysis. The stability of results was found to range from perfectly stable (i.e. all digits of data significant) to highly unstable (i.e. 0 − 1 significant digits). This paper highlights the potential of leveraging induced variance in estimates of brain connectivity to reduce the bias in networks without compromising reliability, alongside increasing the robustness and potential upper-bound of their applications in the classification of individual differences. We demonstrate that stability evaluations are necessary for understanding error inherent to brain imaging experiments, and how numerical analysis can be applied to typical analytical workflows both in brain imaging and other domains of computational sciences, as the techniques used were data and context agnostic and globally relevant. Overall, while the extreme variability in results due to analytical instabilities could severely hamper our understanding of brain organization, it also affords us the opportunity to increase the robustness of findings

Seed Germination Ecophysiology of Acacia dealbata Link and Acacia mearnsii De Wild.: Two Invasive Species in the Mediterranean Basin

Acacia dealbata and A. mearnsii are two invasive species found in coastal, mountain, and riparian Mediterranean habitats. Seed biology and germination traits are important drivers of the competitive performance of plants and may significantly contribute to biological invasions. The seeds of Acacia s.l. have physical dormancy due to an impermeable epidermal layer. The aim of this study was to assess the germination capacity of scarified and non-scarified seeds of A. dealbata and A. mearnsii from different areas of the Mediterranean Basin. To test the seed imbibition capacity, the increase in mass was evaluated. Non-scarified seeds were tested at 15, 20, and 25 C in light conditions. Scarified seeds were tested at 5, 10, 15, 20, and 25 C and 25/10 C in light and dark conditions. Scarified seeds increased in mass more than non-scarified seeds. Both species showed a higher germination capacity at 25 C in non-scarified seeds; A. dealbata reached a germination maximum of 55%, while A. mearnsii reached 40%, showing a difference among these populations. Scarified seeds of both species reached germination percentages >95% at all temperatures except at 5 C in dark conditions. Scarification was necessary to break dormancy and promote germination. The present study provides new knowledge about the seed ecology and germinative behaviour of the two Acacia species under different pre-treatment, temperature, and photoperiod regimes, contributing to the understanding of their invasive behaviour