Catchment drainage network scaling laws found experimentally in overland flow morphologies

The scaling relation between the drainage area and stream length (Hack's law), along with exceedance probabilities of drainage area, discharge, and upstream flow network length, is well known for channelized fluvial regions. We report here on a laboratory experiment on an eroding unconsolidated sediment for which no channeling occurred. Laser scanning was used to capture the morphological evolution of the sediment. High-intensity, spatially nonuniform rainfall ensured that the morphology changed substantially over the 16-hr experiment. Based on the surface scans and precipitation distribution, overland flow was estimated with the D8 algorithm, which outputs a flow network that was analyzed statistically. The above-mentioned scaling and exceedance probability relationships for this overland flow network are the same as those found for large-scale catchments and for laboratory experiments with observable channels. In addition, the scaling laws were temporally invariant, even though the network dynamically changed over the course of experiment

Assessment of Three Mitochondrial Genes (16S, Cytb, CO1) for Identifying Species in the Praomyini Tribe (Rodentia: Muridae)

The Praomyini tribe is one of the most diverse and abundant groups of Old World rodents. Several species are known to be involved in crop damage and in the epidemiology of several human and cattle diseases. Due to the existence of sibling species their identification is often problematic. Thus an easy, fast and accurate species identification tool is needed for non-systematicians to correctly identify Praomyini species. In this study we compare the usefulness of three genes (16S, Cytb, CO1) for identifying species of this tribe. A total of 426 specimens representing 40 species (sampled across their geographical range) were sequenced for the three genes. Nearly all of the species included in our study are monophyletic in the neighbour joining trees. The degree of intra-specific variability tends to be lower than the divergence between species, but no barcoding gap is detected. The success rate of the statistical methods of species identification is excellent (up to 99% or 100% for statistical supervised classification methods as the k-Nearest Neighbour or Random Forest). The 16S gene is 2.5 less variable than the Cytb and CO1 genes. As a result its discriminatory power is smaller. To sum up, our results suggest that using DNA markers for identifying species in the Praomyini tribe is a largely valid approach, and that the CO1 and Cytb genes are better DNA markers than the 16S gene. Our results confirm the usefulness of statistical methods such as the Random Forest and the 1-NN methods to assign a sequence to a species, even when the number of species is relatively large. Based on our NJ trees and the distribution of all intraspecific and interspecific pairwise nucleotide distances, we highlight the presence of several potentially new species within the Praomyini tribe that should be subject to corroboration assessments

Taxonomic hypotheses regarding the genus <em>Gerbillus</em> (Rodentia, Muridae, Gerbillinae) based on molecular analyses of museum specimens

International audienceMethodological improvements now allow routine analyses of highly degraded DNA samples as found in museum specimens. Using these methods could be useful in studying such groups as rodents of the genus Gerbillus for which i) the taxonomy is still highly debated, ii) collection of fresh specimens may prove difficult. Here we address precise taxonomic questions using a small portion of the cytochrome b gene obtained from 45 dry skin/skull museum samples (from 1913 to 1974) originating from two African and three Asian countries. The specimens were labelled G. gerbillus, G. andersoni, G. nanus, G. amoenus, G. perpallidus and G. pyramidum, and molecular results mostly confirmed these assignations. The close relationship between G. nanus (Asian origin) and G. amoenus (African origin) confirmed that they represent vicariant sibling species which differentiated in allopatry on either side of the Red Sea. In the closely related G. perpallidus and G. pyramidum, specimens considered as belonging to one G. pyramidum subspecies (G. p. floweri) appeared closer to G. perpallidus suggesting that they (G. p. floweri and G. perpallidus) may represent a unique species, distributed on both sides of the Nile River, for which the correct name should be G. floweri. Furthermore, the three other G. pyramidum subspecies grouped together with no apparent genetic structure suggesting that they may not yet represent genetically differentiated lineages. This study confirms the importance of using these methods on museum samples, which can open new perspectives in this particular group as well as in other groups of interest

Host cell/Orientia tsutsugamushi interactions: Evolution and expression of syndecan-4 in Asian rodents (Rodentia, Muridae)

Scrub typhus is an acute febrile zoonotic disease and worldwide more than a billion people may be at risk for infection. Orientia tsutsugamushi, the causative agent of scrub typhus, is an obligate intracellular bacterium. Rodents are reported to be the primary reservoir hosts of the disease and according to the most recent surveys, all species within the Rattus sensu lato complex of the tribe Rattini are carriers of scrub typhus. There is no evidence that any of mouse (Mus) species serves as the primary reservoir of the bacterium even when occurring in sympatry with wild infected rats. This contrast in the host/syndecan-4 interactions between Rattini and Asian Murini may be due to intrinsic (i.e., genetic) differences. Herein we compare the sequence and expression levels of syndecan-4 (the putative cell receptor of O. tsutsugamushi) between Rattini species that are known to be natural reservoirs for the typhus agents, and Murini species that are not. Although it was not possible to conclusively link the structural variations detected in syndecan-4 with carrier status in either Rattini and Murini, our findings indicate the absence of a strong Orientia-mediated selective regime acting on gene structure. In contrast, variable spleen-specific syndecan-4 expression levels show a strong correlation between under-expression of syndecan-4 in Murini and seropositive Rattini, compared to seronegative Rattini rodents. We postulate that two divergent responses may be at work in Murini and Rattini, both linked with differential expression of syndecan-4: (i) reduced syndecan-4 transcription in Murini decreases the likelihood that the host cells will become infected by the Orientia bacterium, while (ii) reduced syndecan-4 expression in seropositive Rattini limits the pathogenicity of Orientia and consequently improves the longevity of the rat hosts. These patterns may underpin the poor carrier status of wild mice on the one hand, and the effective role of wild rats as reservoir hosts on the other. © 2012 Elsevier B.V

Rodent host cell/Lassa virus interactions : evolution and expression of alpha-Dystroglycan, LARGE-1 and LARGE-2 genes, with special emphasis on the Mastomys genus

Arenaviruses are usually rodent-borne viruses that constitute a major threat for human health. Among them, Lassa Fever Virus (LFV) occurs in Western Africa where it infects hundreds of thousands of people annually. According to the most recent surveys, LFV is hosted by one of the multimammate rats, Mastomys natalensis, but has never been detected in its sibling and sometimes sympatric species Mastomys erythroleucus. This pattern suggests that intrinsic, i.e. genetic properties underlie such a drastic epidemiological difference (M. natalensis as a reservoir vs. M. erythroleucus as a non-reservoir species). Here we investigate genomic differences between these two closely related rodent species by focusing on three genes that have recently been described as pivotal for LFV/human cell interactions: Dystroglycan (the LFV cellular receptor). LARGE-1 and LARGE-2 (two enzymes that are essential to Dystroglycan functioning). For all three genes, sequence analyses showed that amino-acid chains undergo extremely strong purifying selective pressures, and indicated that no nucleotide (therefore no tertiary structure) change can be advocated to explain species-specific differences in LFV-cellular mediation. Nevertheless, preliminary studies of kidney-specific expression profiles suggested that important species-specific differences exist between Mastomys species. Taking into account current knowledge about LFV-human cell interactions, our results may point towards a possible role for LARGE-1 and LARGE-2 enzymes at the intracellular replication level of the virus, rather than at the LFV-host cell receptor binding step

Consequences of organ choice in describing bacterial pathogen assemblages in a rodent population

International audienceHigh-throughput sequencing technologies now allow for rapid cost-effective surveys of multiple pathogens in many host species including rodents, but it is currently unclear if the organ chosen for screening influences the number and identity of bacteria detected. We used 16S rRNA amplicon sequencing to identify bacterial pathogens in the heart, liver, lungs, kidneys and spleen of 13 water voles (Arvicola terrestris) collected in Franche-Comté, France. We asked if bacterial pathogen assemblages within organs are similar and if all five organs are necessary to detect all of the bacteria present in an individual animal. We identified 24 bacteria representing 17 genera; average bacterial richness for each organ ranged from 1·5 ± 0·4 (mean ± standard error) to 2·5 ± 0·4 bacteria/organ and did not differ significantly between organs. The average bacterial richness when organ assemblages were pooled within animals was 4·7 ± 0·6 bacteria/animal; Operational Taxonomic Unit accumulation analysis indicates that all five organs are required to obtain this. Organ type influences bacterial assemblage composition in a systematic way (PERMANOVA, 999 permutations, pseudo-F 4,51 = 1·37, P = 0·001). Our results demonstrate that the number of organs sampled influences the ability to detect bacterial pathogens, which can inform sampling decisions in public health and wildlife ecology

Comparative population genetics of a parasitic nematode and its host community: The trichostrongylid Neoheligmonella granjoni and Mastomys rodents in southeastern Senegal

Contact: fax: +33 4 9962 3345. E-mail address: [email protected] audienceContrasting host and parasite population genetic structures can provide information about the population ecology of each species and the potential for local adaptation. Here, we examined the population genetic structure of the nematode Neoheligmonella granjoni at a regional scale in southeastern Senegal, using 11 microsatellite markers. Using the results previously obtained for the two main rodent species of the host community, Mastomys natalensis and Mastomys erythroleucus, we tested the hypothesis that the parasite population structure was mediated by dispersal levels of the most vagile host. The results showed similar genetic diversity levels between host and parasite populations, and consistently lower levels of genetic differentiation in N. granjoni, with the exception of one outlying locus with a high F. The aberrant pattern at this locus was primarily due to two alleles occurring at markedly different frequencies in one locality, suggesting selection at this locus, or a closely linked one. Genetic differentiation levels and isolation by distance analyses suggested that gene flow was high and random in N. granjoni at the spatial scale examined. The correlation between pair-wise genetic differentiation levels in the parasite and its main host was consistent with the hypothesis tested. Models of local adaptation as a function of the dispersal rates of hosts and parasites suggest that opportunities for local adaptation would be low in this biological system. (C) 2011 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved