Diversité systématique des Didelphidae (Marsupialia) européens tertiaires

From the early Eocene to the middle Miocene,26 species of european Didelphidae are recognized. The diagnosis of 15 new species are stated (Peradectes louisi, russelli and multigniensis; Amphiperatherium brabantense, bourdellense, gothei, maximum, bastbergense and fontense; Peratherium matronense, sudrei, bretouense, lavergnense, monspeliense and perrierense). For the first time, the sub-family of Didelphinae is divided in two new tribes (Peradectini and Didelphini). In Europe, the story of this sub-family is briefly stated.     

Mitochondrial DNA reveals the genealogical history of the snake-eyed lizards (Ophisops elegans and O. occidentalis) (Sauria: Lacertidae)

The snake-eyed lizards of the genus Ophisops (Lacertidae) have been through a series of taxonomical revisions, but still their phylogenetic relationships remain uncertain. In the present study we estimate the phylogeographic structure of O. elegans across its distributional range and we evaluate the relationships between O. elegans and the sympatric, in North Africa, species O. occidentalis, using partial mtDNA sequences (16S rRNA, COI, and cyt b). All phylogenetic analyses produced topologically identical trees where extant populations of O. elegans and O. occidentalis were found polyphyletic. Taking into account all the potential causes of polyphyly (introgressive hybridization, incomplete lineage sorting, and imperfect taxonomy) we suggest the inaccurate taxonomy as the most likely explanation for the observed pattern. Our results stress the need for re-evaluation of the current taxonomical status of these species and their subspecies. Furthermore, our biogeographic analyses and the estimated time of divergences suggest a late Miocene diversification within these species, where the present distribution of O. elegans and O. occidentalis was the result of several dispersal and vicariant events, which are associated with climatic oscillations (the late Miocene aridification of Asia and northern Africa) and paleogeographic barriers of late Miocene and Pliocene period.     

Location of the first step transfer fragment and single-strand interruptions in T5stO bacteriophage DNA

When Escherichia coli F is infected with T5st0 phage and arrested at the first step of transfer (Lanni, 1968) then centrifuged, the phage capsids are liberated into the medium and the naked phage chromosome, linked to the bacterial membrane by its first step transfer end, is uncoiled without breakage. These statements are based on the study of the distribution of labelled phage DNA between the bacteria and the surrounding medium and have been confirmed by direct observation in the electron microscope. The attached and naked T5st0 chromosome may easily be broken by moderate shearing forces into a small number of precisely sized fragments. By sedimentation analysis on neutral sucrose gradients, it was possible to locate the preferential breaking points at distances of 8, 19, 35 and 60% of the total length of the molecule, measured from the first step transfer end. It is suggested that these weak points coincide with the single-strand breaks present on one of the two chains of the T5st0 chromosome. Evidence is also presented that the first step transfer fragment is (i) immediately attached after injection to a fast sedimenting bacterial component, possibly membrane, (ii) localized at only one end of the chromosome and (iii) possibly separated by a single-strand interruption from the rest of the DNA molecule. It is concluded that the precise location of the preferential breaking points implies that the viral chromosome must be injected into the host following a unique direction.     

Edge effect and structure of mixed-species bird flocks in an Afrotropical lowland forest

Avian mixed-species flocks are a dominant feature of tropical moist forests, yet their cost–benefit balance and habitat dependence in Africa are not fully documented. We recorded the composition of mixed-species bird flocks in a pristine Afrotropical lowland forest site in Salonga NP, DRC. Our data showed that at least four types of flock existed, one of which specialized on edge habitats. We used multivariate analyses to further characterize edge effect on the most documented mixed-species flock type and found a significant effect on flock composition. While neither species guild nor preferential foraging stratum played an important role in flock participation, the nucleus role was played by a different species at the edge and in the interior, and both species abundance and associations were habitat-dependant, suggesting “domino effects” on the structure of mixed-species flocks.     

New contact zone and assemblages among water frogs of Southern France

Water frogs are involved in several hybridogenetic complexes. However, investigations in Southern and Western France produced evidence of new hybridization events between R. lessonae and R. perezi (some new hybrids tadpoles were discovered), and the existence of new assemblages [R–G, L–P, R–P, P–R–G: (R,  ridibunda; G,  grafi; L, lessonae; P,  perezi )]. In respect to hybridogenesis, these assemblages offer opportunities for both primary and secondary hybridizations. Such peculiarities may be explained either by introductions or by relic populations and may influence water frog evolution.     

Phenotypic plasticity allows the Mediterranean parsley frog Pelodytes punctatus to exploit two temporal niches under continuous gene flow

Environmental changes, such as climate change, lead to the opening of new niches. In such situations, species that adapt to new niches can survive and/or expand their ranges. However, gene flow can hamper genetic adaptation to new environments. Alternatively, recent models have highlighted the importance of phenotypic plasticity in tracking environmental change. Here, we investigate whether phenotypic plasticity or genetic evolution (or both) allows an amphibian species to exploit two divergent climatic niches. In the Mediterranean region, the parsley frog Pelodytes punctatus breeds both in spring, as do most other species, and in autumn, a temporal niche not exploited by most other species, but which may become increasingly important with global warming. Conditions of development are dramatically different between the two seasons and deeply impact tadpole life-history traits. To determine whether these temporal niches are exploited by two genetically differentiated subpopulations, or whether the bimodal phenology arises in a panmictic population displaying plastic life-history traits, we use two complementary approaches. We measure both molecular genetic differentiation and quantitative-trait differentiation between spring and autumn cohorts, using microsatellites and common garden experiments, respectively. Seasonal cohorts were not genetically differentiated and differences in tadpole life history between cohorts were not maintained in laboratory conditions. We conclude that phenotypic plasticity, rather than genetic adaptation, allows Parsley frog to exploit two contrasting temporal niches.     

RNase L releases a small RNA from HCV RNA that refolds into a potent PAMP

Triggering and propagating an intracellular innate immune response is essential for control of viral infections. RNase L is a host endoribonuclease and a pivotal component of innate immunity that cleaves viral and cellular RNA within single-stranded loops releasing small structured RNAs with 5′-hydroxyl (5′-OH) and 3′-monophosphoryl (3′-p) groups. In 2007, we reported that RNase L cleaves self RNA to produce small RNAs that function as pathogen-associated molecular patterns (PAMPs). However, the precise sequence and structure of PAMP RNAs produced by RNase L is unknown. Here we used hepatitis C virus RNA as substrate to characterize RNase L mediated cleavage products [named suppressor of virus RNA (svRNA)] for their ability to activate RIG-I like receptors (RLR). The NS5B region of HCV RNA was cleaved by RNase L to release an svRNA that bound to RIG-I, displacing its repressor domain and stimulating its ATPase activity while signaling to the IFN-β gene in intact cells. All three of these RIG-I functions were dependent on the presence in svRNA of the 3′-p. Furthermore, svRNA suppressed HCV replication in vitro through a mechanism involving IFN production and triggered a RIG-I-dependent hepatic innate immune response in mice. RNase L and OAS (required for its activation) were both expressed in hepatocytes from HCV-infected patients, raising the possibility that the OAS/RNase L pathway might suppress HCV replication in vivo. It is proposed that RNase L mediated cleavage of HCV RNA generates svRNA that activates RIG-I, thus propagating innate immune signaling to the IFN-β gene.     

TESTING THE INFLUENCE OF FAMILY STRUCTURE AND OUTBREEDING DEPRESSION ON HETEROZYGOSITY‐FITNESS CORRELATIONS IN SMALL POPULATIONS

Theory predicts that positive heterozygosity‐fitness correlations (HFCs) arise as a consequence of inbreeding, which is often assumed to have a strong impact in small, fragmented populations. Yet according to empirical data, HFC in such populations seem highly variable and unpredictable. We here discuss two overlooked phenomena that may contribute to this variation. First, in a small population, each generation may consist of a few families. This generates random correlations between particular alleles and fitness (AFCs, allele‐fitness correlations) and results in too liberal tests for HFC. Second, in some contexts, small populations receiving immigrants may be more impacted by outbreeding depression than by inbreeding depression, resulting in negative rather than positive HFC. We investigated these processes through a case study in tadpole cohorts of Pelodytes punctatus living in small ponds. We provide evidence for a strong family structure and significant AFC in this system, as well as an example of negative HFC. By simulations, we show that this negative HFC cannot be a spurious effect of family structure, and therefore reflects outbreeding depression in the studied population. Our example suggests that a detailed examination of AFC and HFC patterns can provide valuable insights into the internal genetic structure and sources of fitness variation in small populations.