Modeling and evaluating human-mediated dispersal mechanisms at landscape scale: a study of road network and invasion parameters for Lasius neglectus ants invasive species

International audienceAnts invasive species Biological invasions are considered, right after climate and land use changes, to be one of the principal causes of biodiversity erosion. This phenomenon is related to global change, since climate and land use modifications affect environmental conditions, and are partly responsible for the introduction and proliferation of exotic species into new environments. Furthermore, human-mediated dispersal acts as a dispersal vector for many exotic species, both at the introduction and secondary spread stages. On the one hand, introduction stage is a consequence of human-mediated long distance dispersal, due to human activities (and especially commercial exchanges), and is known to happen at large spatial scales (continental or global scales). On the other hand, secondary spread occurs at smaller spatial and time scales (like landscape scale) and can be provided by natural and human-mediated dispersal mechanisms, once the introduction had brought the exotic species into a novel environment, and after it has succeeded in establishing itself (i.e. survive and reproduce). Few works have pointed out the role of these second stages in small-scale invasive species spread. And yet, a lot of invasive species are susceptible to be partly or completely dispersed by local human processes happening at local spatial and time scales (materials transportation, for example). The lack of consideration for this potential important mode of dispersal seems to be the consequence of multiple factors: human-mediated dispersal is generally considered as a long distance dispersal process, more responsible for invasive species introduction than for secondary spread, it is difficult to qualify and quantify this mode of dispersal because of the multiplicity of potentially involved human activities being its vector, for a given organism that can disperse naturally, it is complicated to distinguish between natural and human-mediated dispersal, as they may occur at similar scale.In this paper, we study the spreading pattern of Lasius neglectus, an invasive ant species originated from Anatoly, which invaded Europe in the last decades and which is currently present in the Rhône valley, in France. We present a numerical model enabling the estimation of multiple human-mediated dispersal parameters, based on ground-truth sampling and minimizing a priori

Towards an understanding of isospin violation in pion-nucleon scattering

We investigate isospin breaking in low-energy pion-nucleon scattering in the framework of chiral perturbation theory. This work extends the systematic analysis of [1] to the energy range above threshold. Various relations, which identically vanish in the limit of isospin symmetry, are used to quantify isospin breaking effects. We study the energy dependence of the S- and P-wave projections of these ratios and find dramatic effects in the S-waves of those two relations which are given in terms of isoscalar quantities only. This effect drops rather quickly with growing center-of-mass energy.Comment: 12 pp, REVTeX, 8 figs, FZJ-IKP(TH)-2000-2

On the size of isospin violation in low-energy pion-nucleon scattering

We present an analysis of isospin-breaking effects in threshold pion-nucleon scattering due to the light quark mass difference and the dominant virtual photon effects. We discuss the deviation from various relations, which are exact in the isospin limit. The size of the isospin-violating effects in the relations involving the isovector $\pi N$ amplitudes is typically of the order of one percent. We also find a new remarkably large effect $(\sim 40$ in an isoscalar triangle relation connecting the charged and neutral pion scattering off protons.Comment: 10 pp, LaTeX, uses epsf, 2 fig

The observed link between urbanization and invasion can depend on how invasion is measured

Aim Cities are thought to promote biological invasions because invasive species are more often introduced in urban areas and because they are more successful in disturbed environments. However, the association is not as strongly supported by the literature as is generally assumed and might depend on how urbanization and invasion are measured. In this study, we test if the type of data used to assess the link between urbanization and invasion can affect a study's conclusions. Location Europe and middle Rhône valley (~5000 km2 in south-eastern France). Method We studied the spatial distribution of the invasive garden ant Lasius neglectus in its current introduced range in Europe and tested its association with urbanization using three measures of invasion (presence-only, presence–absence and population area) and two measures of urbanization (urban/nonurban land cover classification and proportion of impervious surfaces (buildings, road) per spatial unit). Results Based on presence-only data across Europe, L. neglectus occurred in urban areas 10 times more often than expected from a random geographical distribution. However, when controlling for spatial bias in sampling effort with presence–absence data (1870 sampling locations in the middle Rhône valley, France), the occurrence of the species was independent of urbanization. Moreover, the surface occupied by L. neglectus populations was negatively correlated with urbanization. Main conclusions These findings show that the type of occurrence data used to test the link between urbanization and invasion can strongly affect the conclusion of a study. This is particularly concerning because invasion studies often use presence-only data that are likely biased towards cities. Future urban invasions studies must be carefully designed to avoid this pitfall.Peer reviewe

Land-cover and climate factors contribute to the prevalence of the ectoparasitic fungus Laboulbenia formicarum in its invasive ant host Lasius neglectus

International audienceUnderstanding the distribution of parasites is crucial for biodiversity conservation. Here, we studied the distribution of the ectoparasitic fungus Laboulbenia formicarum in native and invasive Lasius ants in a 2000 km2 area. We screened over 16,000 ant workers in 478 colonies of five different species. We found that Lab. formicarum was rare in native Lasius species but infected 58% of the colonies of the invasive species Las. neglectus. At landscape scale, Lab. formicarum presence could not be explained by geographic and genetic distances between Las. neglectus colonies but was associated with hotter and dryer climatic conditions and its prevalence in colonies increased with urbanization. Within infected colonies, fungal prevalence varied from 0 to 100 percent within meters and was negatively correlated with impervious ground cover. In a changing world, our findings emphasize the importance of land-use and climatic factors in shaping the distribution and prevalence of fungal parasites

CD4+ T Cell Count Recovery in HIV Type 1-Infected Patients Is Independent of Class of Antiretroviral Therapy

Background. In recent years, treatment options for human immunodeficiency virus type 1 (HIV-1) infection have changed from nonboosted protease inhibitors (PIs) to nonnucleoside reverse-transcriptase inhibitors (NNRTIs) and boosted PI-based antiretroviral drug regimens, but the impact on immunological recovery remains uncertain. Methods. During January 1996 through May 2007, all patients in the Swiss HIV Cohort were included if they received the first combination antiretroviral therapy (cART) and had known baseline CD4+ T cell counts and HIV-1 RNA values (n=3293). The mean (±SD) duration of follow-up was 26.8±20.5 months. The follow-up time was limited to the duration of the first cART. CD4+ T cell recovery was analyzed in 3 different treatment groups: nonboosted PI, NNRTI, or boosted PI. The end point was the absolute increase of CD4+ T cell count in the 3 treatment groups after the initiation of cART. Results. Two thousand five hundred ninety individuals (78.7%) initiated a nonboosted-PI regimen, 452 (13.7%) initiated an NNRTI regimen, and 251 (7.6%) initiated a boosted-PI regimen. Absolute CD4+ T cell count increases at 48 months were as follows: in the nonboosted-PI group, from 210 to 520 cells/µL; in the NNRTI group, from 220 to 475 cells/µL; and in the boosted-PI group, from 168 to 511 cells/µL. In a multivariate analysis, the treatment group did not affect the response of CD4+ T cells; however, increased age, pretreatment with nucleoside reverse-transcriptase inhibitors, serological tests positive for hepatitis C virus, Centers for Disease Control and Prevention stage C infection, lower baseline CD4+ T cell count, and lower baseline HIV-1 RNA level were risk factors for smaller increases in CD4+ T cell count. Conclusion. CD4+ T cell recovery was similar in patients receiving nonboosted PI-, NNRTI-, and boosted PI-based cAR

Invasiveness of an introduced species: the role of hybridization and ecological constraints

International audienceIntroduced 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 semi-natural 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

Characteristics, Determinants, and Clinical Relevance of CD4 T Cell Recovery to <500 Cells/µL in HIV Type 1—Infected Individuals Receiving Potent Antiretroviral Therapy

Background. The CD4 T cell count recovery in human immunodeficiency virus type 1 (HIV-1)—infected individuals receiving potent antiretroviral therapy (ART) shows high variability. We studied the determinants and the clinical relevance of incomplete CD4 T cell restoration. Methods. Longitudinal CD4 T cell count was analyzed in 293 participants of the Swiss HIV Cohort Study who had had a plasma HIV-1 RNA load .05). Older age (adjusted odds ratio [aOR], 1.71 per 10-year increase; 95% confidence interval [CI], 1.21-2.43), lower baseline CD4 T cell count (aOR, 0.37 per 100-cell increase; 95% CI, 0.28-0.49), and longer duration of HIV infection (aOR, 2.39 per 10-year increase; 95% CI, 1.19-4.81) were significantly associated with a CD4 T cell count <500 cells/µL at 5 years. The median increases in CD4 T cell count after 3-6 months of ART were smaller in incomplete responders (P < .001) and predicted, in conjunction with baseline CD4 T cell count and age, incomplete response with 80% sensitivity and 72% specificity. Conclusion. Individuals with incomplete CD4 T cell recovery to <500 cells/µL had more advanced HIV-1 infection at baseline. CD4 T cell changes during the first 3-6 months of ART already reflect the capacity of the immune system to replenish depleted CD4 T lymphocyte

Extraction of the pion-nucleon sigma-term from the spectrum of exotic baryons

The pion nucleon sigma-term is extracted on the basis of the soliton picture of the nucleon from the mass spectrum of usual and the recently observed exotic baryons, assuming that they have positive parity. The value found is consistent with that inferred by means of conventional methods from pion nucleon scattering data. The study can also be considered as a phenomenological consistency check of the soliton picture of baryons.Comment: 8 pages, 2 figures, references added, discussion extended, to appear in Eur.Phys.J.

Scholarship and security policy: a review of recent literature

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68058/2/10.1177_002200275900300408.pd