Activation of the mammalian heat shock transcription factor (HSF)1 by stress is a multistep process resulting in the transcription of heat shock genes. Coincident with these events is the rapid and reversible redistribution of HSF1 to discrete nuclear structures termed HSF1 granules, whose function is still unknown. Key features are that the number of granules correlates with cell ploidy, suggesting the existence of a chromosomal target. Here we show that in humans, HSF1 granules localize to the 9q11-q12 heterochromatic region. Within this locus, HSF1 binds through direct DNA–protein interaction with a nucleosome-containing subclass of satellite III repeats. HSF1 granule formation only requires the DNA binding competence and the trimerization of the factor. This is the first example of a transcriptional activator that accumulates transiently and reversibly on a chromosome-specific heterochromatic locus.

Histone macroH2A, which is a subtype of histone H2A, possesses a histone H2A-like portion fused to a relatively long non-histone portion. MacroH2A has been shown to associate preferentially with the inactive X chromosome [1]. To investigate the specificity of this association, the nuclear distribution of macroH2A was compared with that of regular core histones. In normal human female fibroblasts, all anti-histone antibodies that were tested (including anti-macroH2A antibody) preferentially labeled the inactive X chromosome. Moreover, when expressed as green fluorescent protein (GFP) fusions, both histone H2A and macroH2A were concentrated in the Barr body. These data clearly show the presence of a higher density of nucleosomes in the inactive X chromosome. Accordingly, the specificity of the macroH2A association with the inactive X chromosome should be reconsidered. While investigating the role of macroH2A, we found that the proximity of the non-histone region of macroH2A to a promoter could lead to a specific repression of transcription, suggesting that the incorporation of macroH2A into chromatin might help to establish the stable pattern of gene expression in differentiated cells.

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Quantifying the impacts of inbreeding and genetic drift on fitness traits in fragmented populations is becoming a major goal in conservation biology. Such impacts occur at different levels and involve different sets of loci. Genetic drift randomly fixes slightly deleterious alleles leading to different fixation load among populations. By contrast, inbreeding depression arises from highly deleterious alleles in segregation within a population and creates variation among individuals. A popular approach is to measure correlations between molecular variation and phenotypic performances. This approach has been mainly used at the individual level to detect inbreeding depression within populations and sometimes at the population level but without consideration about the genetic processes measured. For the first time, we used in this study a molecular approach considering both the interpopulation and intrapopulation level to discriminate the relative importance of inbreeding depression vs. fixation load in isolated and non-fragmented populations of European tree frog (Hyla arborea), complemented with interpopulational crosses. We demonstrated that the positive correlations observed between genetic heterozygosity and larval performances on merged data were mainly caused by co-variations in genetic diversity and fixation load among populations rather than by inbreeding depression and segregating deleterious alleles within populations. Such a method is highly relevant in a conservation perspective because, depending on how populations lose fitness (inbreeding vs. fixation load), specific management actions may be designed to improve the persistence of populations.

Whereas the consequences of global warming at population or community levels are well documented, studies at the cellular level are still scarce. The study of the physiological or metabolic effects of such small increases in temperature (between +2°C and +6°C) is difficult because they are below the amplitude of the daily or seasonal thermal variations occurring in most environments. In contrast, subterranean biotopes are highly thermally buffered (±1°C within a year), and underground water organisms could thus be particularly well suited to characterise cellular responses of global warming. To this purpose, we studied genes encoding chaperone proteins of the HSP70 family in amphipod crustaceans belonging to the ubiquitous subterranean genus Niphargus. An HSP70 sequence was identified in eight populations of two complexes of species of the Niphargus genus (Niphargus rhenorhodanensis and Niphargus virei complexes). Expression profiles were determined for one of these by reverse transcription and quantitative polymerase chain reaction, confirming the inducible nature of this gene. An increase in temperature of 2°C seemed to be without effect on N. rhenorhodanensis physiology, whereas a heat shock of +6°C represented an important thermal stress for these individuals. Thus, this study shows that although Niphargus individuals do not undergo any daily or seasonal thermal variations in underground water, they display an inducible HSP70 heat shock response. This controlled laboratory-based physiological experiment constitutes a first step towards field investigations of the cellular consequences of global warming on subterranean organisms.

No abstract

Introduced species are confronted with new environments to which they need to adapt. However, the ecological success of an introduced species is generally difficult to predict, especially when hybridizations may be involved in the invasion success. In western Europe, the lake frog Pelophylax ridibundus appears to be particularly successful. A reason for this species' success might be the presence of the invader's genetic material prior to the introduction in the form of a hybrid between P. ridibundus and a second indigenous water frog species. These hybrids reproduce by hybridogenesis, only transmitting the ridibundus genome to gametes and backcrossing with the indigenous species (i.e. P. lessonae). This reproductive system allows the hybrid to be independent from P. ridibundus, and allows the ridibundus genome to be more widely spread than the species itself. Matings among hybrids produce newly formed P. ridibundus offspring (N), if the genomes are compatible. Therefore, we hypothesize that hybridogenesis increases the invasiveness of P. ridibundus (1) by enhancing propagule pressure through N individuals, and/or (2) by increasing adaptation of invaders to the native water frogs' habitat through hybrid-derived ridibundus genomes that are locally adapted. We find support for the first hypothesis because a notable fraction of N tadpoles is viable. However, in our seminatural experiments they did not outperform ridibundus tadpoles in the native water frogs' habitat, nor did they differ physiologically. This does not support the second hypothesis and highlights ecological constraints on the invasion. However, we cannot rule out that these constraints may fall with ongoing selection, making a replacement of indigenous species highly probable in the future.

Taxonomy is undoubtedly complementary to other fields in biology such as ecology, and both ecologists and taxonomists increasingly acknowledge that they can profit from phylogenetic ecology or ecological phylogeny, respectively. However, such mutual relations between these disciplines are constrained by traditional focuses on different operational scales: taxonomists are more familiar with large scales (e.g., global, continental, many species of a given clade), whereas ecologists are more familiar with small scales (regional, ecosystems, habitats, few species of a given clade). To foster mutually fruitful, 2-way exchanges between taxonomy and ecology at such smaller scales requires assessments of the small-scale performance of taxonomic practices so far used at larger scales. Such assessments are the objective of this study. To combine quantified ecology and phylogeny at the smaller scale, we designed a research project using 9 species of Hydropsyche (Trichoptera) from the Loire River (i.e., we focus on the regional scale). Here, we tried to unravel the phylogenetic relationships of this regional set of species using (1) many different characters (molecular and morphological characters of larvae and adults), (2) taxonomic congruence instead of total evidence (as the former provides more opportunities for future research on links between different data sets), and (3) an explicit data matrix and analysis methods that are commonly recommended for phylogenetic studies (e.g., maximum parsimony, maximum likelihood, bootstrapping), and we also included traditional, parsimonious, phylogenetic reasoning. Combining these elements, we obtained the following information for the regional Hydropsyche representatives from the Loire: (1) phylogenetic clusters of the species, (2) phylogenetic distances among the species, and (3) phylogenetic polarities of characters (plesioto apomorphies) in the species tree. For our future ecological studies, this will enable (1) establishment of priorities in species selections for experimental approaches, (2) establishment of relationships between ecological and phylogenetic distances, and (3) interpretation of ecological response gradients across the species in the context of evolutionary processes such as adaptation, niche conservatism, or fitness. These future ecological studies will provide elements that in turn should be useful for taxonomists wishing to include small-scale ecological data into their analyses.