Leaf Litter Consumption by Macroarthropods and Burial of their Faeces Enhance Decomposition in a Mediterranean Ecosystem

In many terrestrial ecosystems, large amounts of leaf litter are consumed by macroarthropods. Most of it is deposited as faeces that are easily transferred into deeper soil layers. However, the decomposition of this large pool of organic matter remains poorly studied. We addressed the question of how leaf litter transformation into macroarthropod faeces, and their burial in the soil, affect organic matter decomposition in a Mediterranean dry shrubland. We compared mass loss of intact leaf litter of two dominant shrub species (Quercus coccifera, Cistus albidus) with that of leaf litter-specific faeces from the abundant millipede Ommatoiulus sabulosus. Leaf litter and faeces were exposed in the field for 1 year, either on the soil surface or buried at 5 cm soil depth. Chemical and physical quality of faeces differed strongly from that of leaf litter, but distinctively between the two shrub species. On the soil surface, faeces decomposed faster than intact leaf litter in Quercus, but at similar rates in Cistus. When buried in the soil, faeces and leaf litter decomposed at similar rates in either species, but significantly faster compared to the soil surface, most likely because of higher moisture within the soil enhancing microbial activity. The combined effects of leaf litter transformation into faeces and their subsequent burial in the topsoil led to a 1.5-fold increase in the annual mass loss. These direct and indirect macroarthropod effects on ecosystem-scale decomposition are likely more widespread than currently acknowledged, and may play a particularly important role in drought-influenced ecosystems.     

Identification and Quantitative Determination of Resin Acids from Corsican Pinus pinaster Aiton Oleoresin Using 13C‐NMR Spectroscopy

Twenty‐three resin samples have been obtained by tapping from individual Pinus pinaster adult trees grown in Corsica and submitted to acido‐basic partition. Identification and quantitative determination of resin acids has been carried out using ¹³C‐NMR spectroscopy following a method developed by our group. The main components were dehydroabietic acid (up to 37.6 %), levopimaric acid (up to 35.5 %) and abietic acid (up to 24.7 %). A lignan, pinoresinol, has been identified in some samples. Within the 23 compositions, submitted to k‐means analysis and Principal Component Analysis, two clusters have been perfectly differentiated, whose compositions were dominated by dehydroabietic acid (Group I, M=23.5 %, SD=6.3) and levopimaric acid (Group II, M=21.2 %; SD=6.2), respectively. Both compositions have been observed in the three locations of harvest.     

Breaking the state of the heart: meshless model for cardiac mechanics

Biomechanics and Modeling in Mechanobiology - Cardiac modeling has recently emerged as a promising tool to study pathophysiology mechanisms and to predict treatment outcomes for personalized...     

Variation in Wolbachia cidB gene,but not cidA,is associated with cytoplasmic incompatibility mod phenotype diversity in Culex pipiens

Endosymbiotic Wolbachia bacteria are, to date, considered the most widespread symbionts in arthropods and are the cornerstone of major biological control strategies. Such a high prevalence is based on the ability of Wolbachia to manipulate their hosts' reproduction. One manipulation called cytoplasmic incompatibility (CI) is based on the death of the embryos generated by crosses between infected males and uninfected females or between individuals infected with incompatible Wolbachia strains. CI can be seen as a modification‐rescue system (or mod‐resc) in which paternal Wolbachia produce mod factors, inducing embryonic defects, unless the maternal Wolbachia produce compatible resc factors. Transgenic experiments in Drosophila melanogaster and Saccharomyces cerevisiae converged towards a model where the cidB Wolbachia gene is involved in the mod function while cidA is involved in the resc function. However, as cidA expression in Drosophila males was required to observe CI, it has been proposed that cidA could be involved in both resc and mod functions. A recent correlative study in natural Culex pipiens mosquito populations has revealed an association between specific cidA and cidB variations and changes in mod phenotype, also suggesting a role for both these genes in mod diversity. Here, by studying cidA and cidB genomic repertoires of individuals from newly sampled natural C. pipiens populations harbouring wPipIV strains from North Italy, we reinforce the link between cidB variation and mod phenotype variation fostering the involvement of cidB in the mod phenotype diversity. However, no association between any cidA variants or combination of cidA variants and mod phenotype variation was observed. Taken together our results in natural C. pipiens populations do not support the involvement of cidA in mod phenotype variation.     

Mono- and digalactosyldiacylglycerol composition of dinoflagellates. VIII. Temperature effects and a perspective on the curious case of Karenia mikimotoi as a producer of the unusual, ‘green algal’ fatty acid hexadecatetraenoic acid [16:4(n-3)]

Previous studies have shown that dinoflagellates with different plastid ancestries have distinct differences in the fatty acid compositions and regiochemistries of their chloroplast-associated galactolipids, mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), thus reflecting plastid origin as a major factor in plastid membrane composition. Specifically, dinoflagellates with aberrant plastids (e.g. Karenia brevis, Kryptoperidinium foliaceum and Lepidodinium chlorophorum) possess certain MGDG- and DGDG-associated fatty acids which are not found in peridinin-containing dinoflagellates (the largest group of photosynthetic dinoflagellates with a red algal plastid ancestry which is thought to be an evolutionary precursor to aberrant plastids), but which are common to other algal groups. For example, hexadecatetraenoic acid (16:4(n-3)) is common to green algae and is found in the MGDG and DGDG of L. chlorophorum, which agrees with its green algal plastid ancestry, while hexadecatrienoic acid (16:3) and hexadecadienoic acid (16:2) are found in the MGDG and DGDG of K. foliaceum, which agrees with its diatom plastid ancestry. Notably, 16:4 has been found by others in the total fatty acids and galactolipids of Karenia mikimotoi, but in no other examined members of the Kareniaceae (all of which have plastids of haptophyte origin). However, these findings lack information as to the regiochemistry of 16:4. We have utilized positive-ion electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS to demonstrate that 16:4, which aside from L. chlorophorum is not found conclusively in the MGDG and DGDG of any other dinoflagellates examined to date irrespective of plastid ancestry, is found in K. mikimotoi as 18:5/16:4 (sn-1/sn-2 regiochemistry) MGDG and DGDG, and that its presence is not modulated (i.e. does not become more saturated) with an increase in growth temperature. Considering an aberrant pigment composition as described by others, we present a perspective where galactolipid-associated 16:4 in K. mikimotoi indicates a plastid ancestry more convoluted than for other members of the Kareniaceae.     

Bacterial NHEJ: a never ending story

Double‐strand breaks (DSBs) are the most detrimental DNA damage encountered by bacterial cells. DBSs can be repaired by homologous recombination thanks to the availability of an intact DNA template or by Non‐Homologous End Joining (NHEJ) when no intact template is available. Bacterial NHEJ is performed by sets of proteins of growing complexity from Bacillus subtilis and Mycobacterium tuberculosis to Streptomyces and Sinorhizobium meliloti. Here, we discuss the contribution of these models to the understanding of the bacterial NHEJ repair mechanism as well as the involvement of NHEJ partners in other DNA repair pathways. The importance of NHEJ and of its complexity is discussed in the perspective of regulation through the biological cycle of the bacteria and in response to environmental stimuli. Finally, we consider the role of NHEJ in genome evolution, notably in horizontal gene transfer.     

Reproductive fitness consequences of progenesis: Sex‐specific pay‐offs in safe and risky environments

Progenesis is considered to have an important role in evolution because it allows the retention of both a larval body size and shape in an adult morphology. However, the cost caused by the adoption of a progenetic process in both males and females remains to be explored to explain the success of progenesis and particularly its biased prevalence across the sexes and environments. Here, through an experimental approach, we used a facultative progenetic species, the palmate newt (Lissotriton helveticus) that can either mature at a small size and retain gills or mature after metamorphosis, to test three hypotheses for sex‐specific pay‐offs of progenesis in safe versus risky habitats. Goldfish were used because they caused a higher decline in progenetic than metamorphic newts. We determined that progenetic newts have a lower reproductive fitness than metamorphic newts. We also found that, when compared to metamorphs, progenetic males have lower reproductive activity than progenetic females and that predatory risk affects more progenetic than metamorphic newts. By identifying ultimate causes of the female‐biased sex ratios found in nature, these results support the male escape hypothesis, that is the higher metamorphosis rate of progenetic males. They also highlight that although progenesis is advantageous in advancing the age at first reproduction, it also brings an immediate fitness cost and this, particularly, in hostile predatory environments. This means that whereas some environmental constraints could favour facultative progenesis, some others, such as predation, can ultimately counter‐select progenesis. Altogether, these results improve our understanding of how developmental processes can affect the sexes differently and how species invasions can impair the success of alternative developmental phenotypes.     

Allelopathic effects of volatile organic compounds released from Pinus halepensis needles and roots

The Mediterranean region is recognized as a global biodiversity hotspot. However, over the last decades, the cessation of traditional farming in the north part of the Mediterranean basin has given way to strong afforestation leading to occurrence of abandoned agricultural lands colonized by pioneer expansionist species like Pinus halepensis. This pine species is known to synthesize a wide range of secondary metabolites, and previous studies have demonstrated strong allelopathic potentialities of its needle and root leachates. Pinus halepensis is also recognized to release significant amounts of volatile organic compounds (VOC) with potential allelopathic effects that have never been investigated. In this context, the objectives of the present study were to improve our knowledge about the VOC released from P. halepensis needles and roots, determine if these VOC affect the seed germination and root growth of two herbaceous target species (Lactuca sativa and Linum strictum), and evaluate if soil microorganisms modulate the potential allelopathic effects of these VOC. Thirty terpenes were detected from both, needle and root emissions with β‐caryophyllene as the major volatile. Numerous terpenes, such as β‐caryophyllene, δ‐terpinene, or α‐pinene, showed higher headspace concentrations according to the gradient green needles < senescent needles < needle litter. Seed germination and root growth of the two target species were mainly reduced in presence of P. halepensis VOC. In strong contrast with the trend reported with needle leachates in literature, we observed an increasing inhibitory effect of P. halepensis VOC with the progress of needle physiological stages (i.e., green needle < senescent needle < needle litter). Surprisingly, several inhibitory effects observed on filter paper were also found or even amplified when natural soil was used as a substrate, highlighting that soil microorganisms do not necessarily limit the negative effects of VOC released by P. halepensis on herbaceous target species.     

The Arabidopsis thaliana trehalase is a plasma membrane-bound enzyme with extracellular activity

The lack of trehalose accumulation in most plant species has been partly attributed to the presence of an active trehalase. Although trehalose synthesis enzymes are thought to be cytosolic, and previous studies have indicated that trehalase activity is extracellular, the exact location of the enzyme has not yet been established in plant cell. We present evidence that the yet uncharacterised full-length Arabidopsis trehalase is a plasma membrane-bound protein, probably anchored to the membrane through a predicted N-terminal membrane spanning domain. The full-length AtTRE1, when expressed in yeast can functionally substitute for the extracellularly active trehalase Ath1p, by sustaining the growth of an ath1 null mutant strain on trehalose and at pH 4.8. We further demonstrate that AtTRE1 expressed in yeast is plasma membrane-bound as in plant cell. In light of these findings, the regulation of plant cell endogenous trehalose by trehalase is discussed.     

Estimation of the deformations induced by articulated bodies: Registration of the spinal column

We present a new non-rigid registration algorithm estimating the displacement field generated by articulated bodies. Indeed the bony structures between different patient images may rigidly move while other tissues may deform in a more complex way. Our algorithm tracks the displacement induced in the column by a movement of the patient between two acquisitions. The volumetric deformation field in the whole body is then inferred from those displacements using a linear elastic biomechanical finite element model. We demonstrate in this paper that this method provides accurate results on 3D sets of computed tomography (CT), MR and positron emission tomography (PET) images and that the results of the registration algorithm show significant decreases in the mean, min and max errors.