Dynamical mechanism for sharp orientation tuning in an integrate-and-fire model of a cortical hypercolumn

Orientation tuning in a ring of pulse-coupled integrate-and-fire (IF) neurons is analyzed in terms of spontaneous pattern formation. It is shown how the ring bifurcates from a synchronous state to a non-phase-locked state whose spike trains are characterized by clustered but irregular fluctuations of the interspike intervals (ISIs). The separation of these clusters in phase space results in a localized peak of activity as measured by the time-averaged firing rate of the neurons. This generates a sharp orientation tuning curve that can lock to a slowly rotating, weakly tuned external stimulus. Under certain conditions, the peak can slowly rotate even to a fixed external stimulus. The ring also exhibits hysteresis due to the subcritical nature of the bifurcation to sharp orientation tuning. Such behavior is shown to be consistent with a corresponding analog version of the IF model in the limit of slow synaptic interactions. For fast synapses, the deterministic fluctuations of the ISIs associated with the tuning curve can support a coefficient of variation of order unity.<br/

Trypanosomatidae from wild mammals in the neotropical rainforest of French Guiana

The initial filling of the reservoir behind the Petit Saut hydro-electric dam, on the Sinnamary River in French Guiana, threatened the terrestrial and arboreal animals living in the neotropical rainforest from being flooded. During a rescue programme between 24 October and 12 November in 1994, many of these animals were checked for infection with trypanosomatids. Overall, 45 blood samples and 54 skin biopsies were collected from 53 mammals (of 13 species representing five orders) and blood samples were also taken from each of nine reptiles (six species from four families). When the skin biopsies and the buffy-coats from the blood samples were cultured in NNN medium, 10 of the cultures, each initiated with mammalian blood, were found to be positive for trypanosomatids. Multilocus enzyme electrophoresis (MLEE) on cellulose acetate plates, with 20 enzyme systems, was then used to investigate each of the positive cultures. The results were analysed by clustering from a genetic distance matrix, using the unweighted pair group method with arithmetic averages (UPGMA), and applying a bootstrap procedure to Wagner parsimony trees. A stock obtained from #Didelphis marsupialis was identified as a zymodeme of #Trypanosoma cruzi (Miles' zymodeme 1) known to cause Chagas disease in French Guiana. Five stocks (one each from #Bradypus tridactylus, #Tamandua tetradactyla and #Alouatta seniculus and two from #Saguinus midas) were of a single zymodeme close to #Trypanosoma rangeli reference stock RGB. This is the first confirmation of the presence of #Tr. rangeli in French Guiana, and the first time that it has been identified, by iso-enzyme analysis, in the neotropical primates #A. seniculus and #S. midas. Two other stocks, isolated from #Choloepus didactylus, were related to #Endotrypanum schaudinni reference stock LEM 2790... (D'après résumé d'auteur

Distribution of two sympatric species of sloths (Choloepus didactylus and Bradypus tridactylus) along the Sinnamary River, French Guiana

Dans le cadre de la mise en eau du barrage de Petit Saut en Guyane française, une opération de sauvetage de la faune s'est déroulée pendant 17 mois. Plus de 900 paresseux (#Bradypus tridactylus et #Chloepus didactylus) ont été capturés le long du fleuve Sinnamary dans une forêt tropicale primaire peu perturbée au départ. Les densités brutes ont été estimées à 1.7 #B. tridactylus/km2 et 0.9 #C. didactylus/km2. La distribution des captures le long des fleuves était relativement continue pour les deux espèces : les variations reflètent vraisemblablement des biais liés aux méthodes de capture. Les plus fortes densités de captures se situaient principalement dans des zones marécageuses. Au cours des premiers mois, et dû à des probabilités de repérage différentes entre les deux espèces, les captures de #B. tridactylus$ ont prédominé, nous avons capturé plus de 73 pour cent d'individus solitaires et 23-24 pour cent de femelles portant un jeune. Ceci amène le pourcentage des animaux capturés solitaires à 96 pour cent des animaux émancipés. (Résumé d'auteur

Testing a global standard for quantifying species recovery and assessing conservation impact.

Recognizing the imperative to evaluate species recovery and conservation impact, in 2012 the International Union for Conservation of Nature (IUCN) called for development of a "Green List of Species" (now the IUCN Green Status of Species). A draft Green Status framework for assessing species' progress toward recovery, published in 2018, proposed 2 separate but interlinked components: a standardized method (i.e., measurement against benchmarks of species' viability, functionality, and preimpact distribution) to determine current species recovery status (herein species recovery score) and application of that method to estimate past and potential future impacts of conservation based on 4 metrics (conservation legacy, conservation dependence, conservation gain, and recovery potential). We tested the framework with 181 species representing diverse taxa, life histories, biomes, and IUCN Red List categories (extinction risk). Based on the observed distribution of species' recovery scores, we propose the following species recovery categories: fully recovered, slightly depleted, moderately depleted, largely depleted, critically depleted, extinct in the wild, and indeterminate. Fifty-nine percent of tested species were considered largely or critically depleted. Although there was a negative relationship between extinction risk and species recovery score, variation was considerable. Some species in lower risk categories were assessed as farther from recovery than those at higher risk. This emphasizes that species recovery is conceptually different from extinction risk and reinforces the utility of the IUCN Green Status of Species to more fully understand species conservation status. Although extinction risk did not predict conservation legacy, conservation dependence, or conservation gain, it was positively correlated with recovery potential. Only 1.7% of tested species were categorized as zero across all 4 of these conservation impact metrics, indicating that conservation has, or will, play a role in improving or maintaining species status for the vast majority of these species. Based on our results, we devised an updated assessment framework that introduces the option of using a dynamic baseline to assess future impacts of conservation over the short term to avoid misleading results which were generated in a small number of cases, and redefines short term as 10 years to better align with conservation planning. These changes are reflected in the IUCN Green Status of Species Standard