Evolution des Asteropyginae (Trilobita) et variations eustatiques au Dévonien

La sous-famille Asteropyginae regroupe des Trilobites de la Famille Dalmanitidae qui se sont développés pendant environ 40 millions d'années, du Lochkovien au Frasnien (Dévonien). Leur extension géographique, des Appalaches à la Birmanie, et leur diversification spécifique (225 espèces environ), ont subi des variations pendant cette période. La comparaison des changements de paléoenvironnement avec l'évolution des Asteropyginae, en particulier sur la base des courbes de variations eustatiques, montre la possibilité de relations entre les deux phénomènes. Après une période lente de diversification des Asteropyginae au Lochkovien-Praguien en Europe el en Afrique du Nord, le processus s'accélère au cours de l'Emsien conduisant au nombre maximal de genres et d'espèces. Au passage Emsien-Eifelien. une phase transgressive provoque une crise importante au sein de ce groupe, Pendant le Givetien et le Frasnien inférieur se produit une deuxième phase de développement, moins importante que la précédente, mais qui est accentuée par la radiation adaptative liée à la migration du groupe vers les Appalaches et l'Afghanistan. Cette phase est interrompue au Frasnien supérieur. Le groupe décline alors et ne franchit pas la limite Frasnien-Famennien, l'extinction se situe juste sous l'événement ‘Kellwasser supérieur’, phase de transgression maximale. *Trilobites, Asteropyginae, Devonien, Evolution, Environnement. The subfamily Asteropyginae brings together trilobites of the family Dalmanitidae, which developed for about 40 million years from the Lochkovian to the Frasnian (Devonian). Their geographical extension, from the Appalachian Mountains to Burma, and their specific diversification (about 225 species) underwent variations during that time. The comparison of the palaeoenvironmental changes with the evolution within Asteropyginae, particularly on the basis of eustatic variation curves, shows possible relations between the two phenomena. After a slow diversification period of the Asteropyginae in Europe and North Africa during the Lochkovian and the Pragian, the process accelerates in the course of the Emsian, thus leading to the maximum number of genera and species. Near the Emsian-Eifelian boundary, a transgressive phase produces a dramatic crisis within the group. During the Givetian and the Lower Frasnian a second phase occurs, less important than the former, but which is accentuated by the adaptive radiation linked with the group's migration toward the Appalachians and Afghanistan. An important change occurs during the Upper Frasnian. The group declines and fails to cross the Frasnian-Famennian boundary; its extinction takes place just beneath the Upper Kellwasser event, the phase of maximum transgression.     

Androgen Regulation of Avian Premigratory Hyperphagia and Fattening: From Eco-Physiology to Neuroendocrinology

In many high latitude-breeding avian species, reproductive andwintering seasons are separated by migratory periods that involvedramatic physiological and behavioral adjustments such as hyperphagiaand fat deposition. The endocrine mechanisms responsible forthese adjustments have been extensively studied, yet remainonly partly understood. The currently available informationindicates that food consumption and/or fattening can be experimentallymodulated by multiple hormones including testosterone, prolactin,glucocorticoids, and opioids. These hormones may control migratoryfunctions through mutual interactions rather than independently.Little is known, however, concerning the nature of these interactionsand their relative importance in the control of annual cyclesin natural conditions. This paper focuses on the role of gonadalandrogens in the control of migratory functions, and it summarizesthe information which is available on the physiological andbehavioral interactions between these androgens and other hormones.     

NADH and NADPH Dependent Malate Dehydrogenases of Phaseolus vulgaris

French bean (Phaseolus vulgaris L. cv. Contender) leaf extracts catalyse the reduction of oxaloacetate to malate in the presence of NADH and NADPH. Under the experimental conditions used, the optimum pH values are 8 and 6 respectively. After chromatography on diethylaminoethyl cellulose, two principal forms of NADH-MDH (L-malate: NAD⁺ oxidoreductase, E.C. 1.1.1.37) upon which NADPH activities are superposed, can be characterized. This result is confirmed by electrophoresis on polyacrylamide gel. On the other hand, after filtration on Ultrogel 34, NADH-MDH is eluted as a single peak; once again, NADPH activity is associated with it. When PtCl^2?₄, a powerful inhibitor of MDH, is added to the reaction medium, the degree of inhibition is the same irrespective of the cofactor employed. When root extracts are submitted to chromatography on diethylaminoethyl cellulose, activity profiles are identical to those obtained with leaves. These results suggest that the NAD dependent enzymes can also utilize NADP to reduce oxaloacetate. After addition of dithiothreitol, another NADPH-MDH activity manifests itself in the leaf extracts; it differs from the foregoing ones in its optimum pH, its chromatographic properties and its response to PtCl^2?₄ action. Root extracts do not exhibit this activity thus showing a specific localization of this enzyme in the green part of the plant.     

Diagnosing the environmental causes of the decline in Grey Partridge Perdix perdix survival in France

We studied Grey Partridge Perdix perdix mortality during breeding to identify the environmental causes of a long‐term decline in adult survival. We radiotagged and monitored daily from mid‐March to mid‐September 1009 females on ten contrasting study sites in 1995‐97. Simultaneously, we recorded habitat features and estimated the abundance of Hen and Marsh Harriers Circus cyaneus and C. aeruginosus Red Fox Vulpes vulpes and mustelids. We experimentally tested whether scavenging could have biased predation rates. We also examined, through the necropsy of 80 carcasses of Grey Partridge, whether disease, parasites or poisoning could have been ultimate causes of high predation rates. The survival rate of radiotagged females during spring and summer ranged from 0.25 to 0.65 across study areas. Mortality peaked in May, June and July when females were laying and incubating. The direct negative impact of farming practices was low (6%). Predation was the main proximate cause of female mortality during breeding (73%) and determined the survival rate, suggesting no compensation by other causes of mortality. Ground carnivores were responsible for 64% of predation cases, and raptors for 29%, but this proportion varied across study sites. Disease and poisoning did not appear to favour predation, and scavenging was not likely to have substantially overestimated predation rates. The predation rate on breeding females was positively correlated with the abundance of Hen and Marsh Harriers, suggesting an additional mortality in areas where harriers were abundant. The proportion of raptor predation was linearly related to harrier abundance. The predation rate was not correlated with the abundance of the Red Fox and mustelids. A potential density‐dependent effect on the predation rate was confounded by the abundance of harriers. We found no convincing relationship between the predation rate and habitat features, but we observed a positive relationship between the abundance of Hen and Marsh Harriers and the mean field size. This suggested that habitat characteristics may contribute to high predation rates through predator abundance or habitat‐dependent predation.     

Multi-scale analysis of responses of stream macrobenthos to forestry activities and environmental context

1. Forestry activities can greatly modify the structure and function of invertebrate communities in streams, but the ability to detect effects of forestry may depend on the spatial scale considered, the choice of response metric and the environmental context. In this study, a multi‐scale, multi‐metric approach was used to compare the usefulness of proximate and larger‐scale measurements of forestry activity for understanding the impacts of forestry on stream macrobenthos. 2. Site‐specific responses of macrobenthic communities to forestry activities measured at four spatial scales (sub‐basin and 8‐, 2‐ and 0.5‐km radii upstream of study sites) were examined for 90 riffle sites distributed among 22 tributary streams (Strahler order 1–5) of the Cascapedia River basin, Quebec, Canada. 3. Multiple regression models and canonical correspondence analysis were used to relate six biological metrics (taxonomic richness, numerical density, biomass density, normalised biomass spectrum, individual body mass and community structure) to variables quantifying logging 1–19 years prior to the study and road density. Environmental predictors (variables quantifying local habitat or landscape features) were included in all analyses to statistically account for environmental context and increase the likelihood of detecting potentially subtle forestry impacts. 4. Forestry activities measured at the larger (sub‐basin and 8 km) scales were linked to decline in taxonomic richness, increase in numerical and biomass densities and shift in size structure of benthic macroinvertebrates, indicating that analyses encompassing larger areas, up to the full basin, may allow for more sensitive detection of effects than those of more limited span. 5. These responses primarily reflected marked increases in the abundance of chironomids and decline in the number of trichopteran taxa with increasing areal coverage of recent (≤2–4 years) cuts, suggesting that larger, longer‐lived and possibly more specialised taxa were more vulnerable to forestry impacts than smaller, multivoltine, generalist invertebrates. After partialling out the influence of other variables, rapid decline in richness occurred even when <1% of the basin had been clear cut in the year prior to the study. 6. Effects of forestry were detected after statistically accounting for natural environmental variability, which may have otherwise concealed those effects. The combined use of multiple biological metrics, partialling out of environmental effects and measurement of impacts at multiple spatial scales may be a broadly applicable approach for enhancing sensitivity and facilitating interpretation in studies of anthropogenic effects on macroinvertebrate communities.