Les affects au coeur des préoccupations urbaines et urbanistiques : la réintroduction du sensible pour penser et concevoir la ville.

Les affects : un nouvel objet du savoir ? Les affects urbains (et leur corollaire le rapport affectif à la ville) mobilisent à côté des dimensions morphologiques, socio-démographiques et structuro-fonctionnelles, un nouveau référentiel en termes d'analyse urbaine : le registre socio-affectif. Notre propos vise ici à faire état de ce courant émergent et des perspectives de recherche s'y rapportant, à travers une explicitation des différents enjeux théoriques, pragmatiques et méthodologiques soulevés par la mobilisation de ce référentiel. Transversalement, il s'agira premièrement de proposer un modèle hypothétique de lecture des prises affectives potentielles offertes aux citadins pour tenter de modéliser conceptuellement la constitution des rapports affectifs des individus envers la ville. Deuxièmement, il s'agira de comprendre les relations parfois antagonistes que les citadins entretiennent avec leurs villes de manière à savoir si ce rapport peut être un moyen d'action susceptible d'améliorer ou de modifier la relation individu/ville et à terme les pratiques urbanistiques.

Cryptic recombination in the ever-young sex chromosomes of Hylid frogs.

Sex chromosomes are expected to evolve suppressed recombination, which leads to degeneration of the Y and heteromorphism between the X and Y. Some sex chromosomes remain homomorphic, however, and the factors that prevent degeneration of the Y in these cases are not well understood. The homomorphic sex chromosomes of the European tree frogs (Hyla spp.) present an interesting paradox. Recombination in males has never been observed in crossing experiments, but molecular data are suggestive of occasional recombination between the X and Y. The hypothesis that these sex chromosomes recombine has not been tested statistically, however, nor has the X-Y recombination rate been estimated. Here, we use approximate Bayesian computation coupled with coalescent simulations of sex chromosomes to quantify X-Y recombination rate from existent data. We find that microsatellite data from H. arborea, H. intermedia and H. molleri support a recombination rate between X and Y that is significantly different from zero. We estimate that rate to be approximately 10(5) times smaller than that between X chromosomes. Our findings support the notion that very low recombination rate may be sufficient to maintain homomorphism in sex chromosomes.

La structure de la carte géographique : approche épistémologique ternaire

Cet article prend pour objet les aspects pragmatiques de la carte géographique à travers un référentiel épistémologique ternaire explicite. Ainsi le regard sur la structure de la carte fait référence à une logique de juxtaposition|superposition/imbrication permettant d'aborder les questions d'échelle et de légende, les deux axes coordonnateurs structurant le champ de la représentation du territoire en carte. Leur interaction commande l'émergence, dans l'espace de l'entre-deux, du tiers concept diagonal, celui de l'implantation cartographique, la carte elle-même, obéissant à ses propres règles de représentation schématique.

Density, climate and varying return points: an analysis of long-term population fluctuations in the threatened European tree frog.

Experimental research has identified many putative agents of amphibian decline, yet the population-level consequences of these agents remain unknown, owing to lack of information on compensatory density dependence in natural populations. Here, we investigate the relative importance of intrinsic (density-dependent) and extrinsic (climatic) factors impacting the dynamics of a tree frog (Hyla arborea) population over 22 years. A combination of log-linear density dependence and rainfall (with a 2-year time lag corresponding to development time) explain 75% of the variance in the rate of increase. Such fluctuations around a variable return point might be responsible for the seemingly erratic demography and disequilibrium dynamics of many amphibian populations.

Genetic bottlenecks driven by population disconnection.

Connectivity among populations plays a crucial role in maintaining genetic variation at a local scale, especially in small populations affected strongly by genetic drift. The negative consequences of population disconnection on allelic richness and gene diversity (heterozygosity) are well recognized and empirically established. It is not well recognized, however, that a sudden drop in local effective population size induced by such disconnection produces a temporary disequilibrium in allelic frequency distributions that is akin to the genetic signature of a demographic bottleneck. To document this effect, we used individual-based simulations and empirical data on allelic richness and gene diversity in six pairs of isolated versus well-connected (core) populations of European tree frogs. In our simulations, population disconnection depressed allelic richness more than heterozygosity and thus resulted in a temporary excess in gene diversity relative to mutation drift equilibrium (i.e., signature of a genetic bottleneck). We observed a similar excess in gene diversity in isolated populations of tree frogs. Our results show that population disconnection can create a genetic bottleneck in the absence of demographic collapse.

Stronger transferability but lower variability in transcriptomic- than in anonymous microsatellites: evidence from Hylid frogs.

A simple way to quickly optimize microsatellites in nonmodel organisms is to reuse loci available in closely related taxa; however, this approach can be limited by the stochastic and low cross-amplification success experienced in some groups (e.g. amphibians). An efficient alternative is to develop loci from transcriptome sequences. Transcriptomic microsatellites have been found to vary in their levels of cross-species amplification and variability, but this has to date never been tested in amphibians. Here, we compare the patterns of cross-amplification and levels of polymorphism of 18 published anonymous microsatellites isolated from genomic DNA vs. 17 loci derived from a transcriptome, across nine species of tree frogs (Hyla arborea and Hyla cinerea group). We established a clear negative relationship between divergence time and amplification success, which was much steeper for anonymous than transcriptomic markers, with half-lives (time at which 50% of the markers still amplify) of 1.1 and 37 My, respectively. Transcriptomic markers are significantly less polymorphic than anonymous loci, but remain variable across diverged taxa. We conclude that the exploitation of amphibian transcriptomes for developing microsatellites seems an optimal approach for multispecies surveys (e.g. analyses of hybrid zones, comparative linkage mapping), whereas anonymous microsatellites may be more informative for fine-scale analyses of intraspecific variation. Moreover, our results confirm the pattern that microsatellite cross-amplification is greatly variable among amphibians and should be assessed independently within target lineages. Finally, we provide a bank of microsatellites for Palaearctic tree frogs (so far only available for H. arborea), which will be useful for conservation and evolutionary studies in this radiation.

Recombination is suppressed and variability reduced in a nascent Y chromosome.

Several hypotheses have been elaborated to account for the evolutionary decay commonly observed in full-fledged Y chromosomes. Enhanced drift, background selection and selective sweeps, which are expected to result from reduced recombination, may all share responsibilities in the initial decay of proto-Y chromosomes, but little empirical information has been gathered so far. Here we take advantage of three markers that amplify on both of the morphologically undifferentiated sex chromosomes of the European tree frog (Hyla arborea) to show that recombination is suppressed in males (the heterogametic sex) but not in females. Accordingly, genetic variability is reduced on the Y, but in a way that can be accounted for by merely the number of chromosome copies per breeding pair, without the need to invoke background selection or selective sweeps.

Buccal swabs allow efficient and reliable microsatellite genotyping in amphibians

Buccal swabs have recently been used as a minimally invasive sampling method in genetic studies of wild populations, including amphibian species. Yet it is not known to date what is the level of reliability for microsatellite genotypes obtained using such samples. Allelic dropout and false alleles may affect the genotyping derived from buccal samples. Here we quantified the success of microsatellite amplification and the rates of genotyping errors using buccal swabs in two amphibian species, the Alpine newt Triturus alpestris and the Green tree frog Hyla arborea, and we estimated two important parameters for downstream analyses, namely the number of repetitions required to achieve typing reliability and the probability of identity among genotypes. Amplification success was high, and only one locus tested required two to three repetitions to achieve reliable genotypes, showing that buccal swabbing is a very efficient approach allowing good quality DNA retrieval. This sampling method which allows avoiding the controversial toe-clipping will likely prove very useful in the context of amphibian conservation.