The influence of fire on the phenological behaviour of Mediterranean plant species in Bas-Languedoc (southern France)

Fire is an ancient ecological factor influencing the Mediterranean vegetation of southern France. The study was carried out on three areas to determine the phenological behaviour of plants with regard to fire. First we studied the flowering responses of perennials in relation to the time since fire: in a Quercus coccifera garrigue most species flower during the year following burning. In comparing species by species between burned and unburned areas most species did not show major differences in the phenological stages. However, fire did increase the number of inflorescences of grasses. A phenological synthesis showed that differences at the community level existed for the flowering stages between the burned areas and the unburned control sites during the first and second years following fire. The growth of some woody species was also studied; the elongation and growth of the plants were biggest during the first or second year after fire. The lack of differences in phenological response between burned and unburned plants may be an adaptive trait to fire.     

Influence of glyoxylic acid on properties of isolated mitochondria]

Glyoxalate is an effector of oxidative phosphorylation in isolated mitochondria : it slows down State 3 but does not affect State 4 respiration. This report presents the findings of our study on the mechanism of action of glyoxalate ; these findings are listed below. The inhibition of Stage 3 respiration by glyoxalate does not set in immediately, can be reversed in part by the addition of an uncoupling agent or a dithiol, is non-competitive against succinate and can be demonstrated with substrates requiring the involvement of other membrane transport systems. Glyoxalate prevents the increased oxygen uptake stimulated by 2,4-DNP or Sr++. Glyoxalate also inhibits phosphate transport and this inhibition can account for most of the effect observed. The inhibition of State 3 respiration is paralleled by a decrease in the mitochondrial accumulation of succinate : this decrease could arise from a direct effect of glyoxalate on dicarboxylic acid transport or could be the result of an inhibiton of the phosphate transport system, which is connected with the former. The decrease in the respiratory rate of uncoupled mitochondria placed in a phosphate free medium demonstrates that the effector acts directly at the substrate transport or/and electron transfer level. Phosphate, by delaying the respiratory inhibiton due to glyoxalate, has a protecting effect on mitochondrial functions. Glyoxalate is thus acting at several mitochondrial sites. It acts presumably by forming hemimercaptals, blocking sulfhydryl groups. Its effects can be accounted for by the unfolding of such (hemicercaptal) groups under the influence of ADP, Pi, uncoupling or others agents which bring about conformational changes in the internal mitochondrial membrane.     

Fast tracer efflux from membrane vesicles; investigation by controlled elution

A method has been developed to study tracer efflux from membrane vesicles. Vesicles are trapped on filters, but in contrast to conventional filtration techniques tracer efflux is measured as such. A functional integration of a commercial fraction collector, a pulse generator, and a programmable repetitive pipet with a simple electronic circuit allows monitoring of complete efflux kinetics from seconds onward. The automatic control of discrete elution steps guarantees reproducible results and makes possible a correction for background release of tracer from the filter. The dependence of efflux data on selected combinations of filters is demonstrated. These experiments also shed some light on problems intrinsic to conventional filtration procedures. The performance of the controlled elution technique is shown with ²²Na efflux from Na channel-rich membrane vesicles.     

Biogeographical network analysis of plant species distribution in the Mediterranean region

The delimitation of bioregions helps to understand historical and ecological drivers of species distribution. In this work, we performed a network analysis of the spatial distribution patterns of plants in south of France (Languedoc‐Roussillon and Provence‐Alpes‐Côte d'Azur) to analyze the biogeographical structure of the French Mediterranean flora at different scales. We used a network approach to identify and characterize biogeographical regions, based on a large database containing 2.5 million of geolocalized plant records corresponding to more than 3,500 plant species. This methodology is performed following five steps, from the biogeographical bipartite network construction to the identification of biogeographical regions under the form of spatial network communities, the analysis of their interactions, and the identification of clusters of plant species based on the species contribution to the biogeographical regions. First, we identified two sub‐networks that distinguish Mediterranean and temperate biota. Then, we separated eight statistically significant bioregions that present a complex spatial structure. Some of them are spatially well delimited and match with particular geological entities. On the other hand, fuzzy transitions arise between adjacent bioregions that share a common geological setting, but are spread along a climatic gradient. The proposed network approach illustrates the biogeographical structure of the flora in southern France and provides precise insights into the relationships between bioregions. This approach sheds light on ecological drivers shaping the distribution of Mediterranean biota: The interplay between a climatic gradient and geological substrate shapes biodiversity patterns. Finally, this work exemplifies why fragmented distributions are common in the Mediterranean region, isolating groups of species that share a similar eco‐evolutionary history.     

Microrépartition des populations de truite commune (Salmo trutta L.) de juvenile de saumon atlantique (Salmo salar L.) et des autres espès préntes dans la partie haute du Scorff (Bretagne)

Resume Une étude de la microrártition de la population de truite commune (Salmo trutta L.) et du juvénile de Saumon atlantique (Salmo salar L.) associée aux autres espès préntes est effectuée en fin d'été dans la partie amont du Scorff (distance source-estuaire 65 km).La population de saumon est composée uniquement d'individus d'âge 0⁺ alors que les truites ont entre 0⁺ et 3⁺ ans avec une majorité pour la classe d'âge des 1⁺ an. La densité de saumon augmente avec la vitesse de courant (r = 0,99) et la taille de la granulométrie du substrat. Un habitat trés favorable à l'espèce se caractérise par une faible profondeur (> 23 cm), une vitesse de courant élevée (61 cm/ s) et un substrat caillouteux. 75,4% de la population est recensée en plein courant.L'effet rive, est particulièrement important pour la truite quelque soit son âge (80,1%). L'absence de la truite 0⁺ du faciés à courant élevé et sa localisation près des berges dans les zones courantes (41 cm/ s) peu profondes entraînent une ségrégation spatiale avec le saumon de même âge. La truite d'au moins un an est présente dans des milieux plus profonds (27 cm) à vitesse de courant nulle à moyenne (< 28 cm/ s). L'effet rive est renforcée par la présence de nombreux courants en berge.Parmi les espéces d'accompagnement, le chabot a la distribution la plus large. La loche et la lamproie de Planer sont les espéces les plus abondantes et ont des densités très élevées dans des secteurs caractéristiques.L'ensemble de ces résultats est discuté en liaison avec les premières observations concernant la distribution de ces espèces sur le cours principal du Scorff.

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We describe the microdistribution of populations of Brown Trout (Salmo trutta L.) and of juvenile atlantic Salmon (Salmo salar L.) in the upstream part of the Scorff river (Brittany) at the end of summer.The Salmon population was composed of one age classe (0⁺) only while Trout age varied from 0⁺ to 3⁺ years, with a majority in age class 1⁺. Salmon density increased with current velocity (r = 0.99) and the nature of the substratum. A very favorable habitat for this species was characterized by reduced depth (< 23 cm), a high current velocity (61 cm s ¹) and a stony substrate. The largest part of the population (74%) was localized in the centre of the running open water.A bank effect was particularly important for brown trout, irrespective of age (80.1%). The trout 0⁺ is absent from shallow rifles and its presence in the few deep running water areas (41 cm s^–1) along the banks involved a spatial segregation with salmon 0⁺. The trout of one year and older were localized in deeper habitats (27 cm) with zero to medium current velocity (< 28 cm s^–1). The bank effect was intensified by the presence of many overhangs along the bank.Among the secondary species, sculpin had the widest distribution, but Stone-loach and brook lamprey were the most abundant species and reached high densities in characteristic areas.

     

March flies and European Cenozoic palaeoclimates (Diptera: Bibionidae)

The proportions of the different bibionid genera are used to estimate the temperature changes between the Late Eocene and the Late Miocene in Western Europe. The genus Plecia is a good indicator of the warm Cenozoic palaeoclimates. We propose a new approach for the estimation of the value of the palaeoclimatic information that could be obtained by actualistic inferences using extinct taxa. Other taxa (i.e. Mastotermitidae) that could appear a priori better palaeoclimatic indicators result to be less sensitive than bibionids to temperature changes. Intraspecific and intrageneric morphological diversity is explored for the genera Bibio, Penthetria and Plecia, showing the difficulties to characterize the fossil bibionid species.