Temporal sampling helps unravel the genetic structure of naturally occurring populations of a phytoparasitic nematode. 2. Separating the relative effects of gene flow and genetic drift

International audienceStudying wild pathogen populations in natural ecosystems offers the opportunity to better understand the evolutionary dynamics of biotic diseases in crops and to enhance pest control strategies. We used simulations and genetic markers to investigate the spatial and temporal population genetic structure of wild populations of the beet cyst nematode Heterodera schachtii on a wild host plant species, the sea beet (Beta vulgaris spp. maritima), the wild ancestor of cultivated beets. Our analysis of the variation of eight microsatellite loci across four study sites showed that (i) wild H. schachtii populations displayed fine-scaled genetic structure with no evidence of substantial levels of gene flow beyond the scale of the host plant, and comparisons with simulations indicated that (ii) genetic drift substantially affected the residual signals of isolation-by-distance processes, leading to departures from migration–drift equilibrium. In contrast to what can be suspected for (crop) field populations, this showed that wild cyst nematodes have very low dispersal capabilities and are strongly disconnected from each other. Our results provide some key elements for designing pest control strategies , such as decreasing passive dispersal events to limit the spread of virulence among field nematode populations

How Ebola Impacts Genetics of Western Lowland Gorilla Populations

12 pagesInternational audienceBackground: Emerging infectious diseases in wildlife are major threats for both human health and biodiversity conservation. Infectious diseases can have serious consequences for the genetic diversity of populations, which could enhance the species' extinction probability. The Ebola epizootic in western and central Africa induced more than 90% mortality in Western lowland gorilla population. Although mortality rates are very high, the impacts of Ebola on genetic diversity of Western lowland gorilla have never been assessed. Methodology/Principal Findings: We carried out long term studies of three populations of Western lowland gorilla in the Republic of the Congo (Odzala-Kokoua National Park, Lossi gorilla sanctuary both affected by Ebola and Lossi's periphery not affected). Using 17 microsatellite loci, we compared genetic diversity and structure of the populations and estimate their effective size before and after Ebola outbreaks. Despite the effective size decline in both populations, we did not detect loss in genetic diversity after the epizootic. We revealed temporal changes in allele frequencies in the smallest population. Conclusions/Significance: Immigration and short time elapsed since outbreaks could explain the conservation of genetic diversity after the demographic crash. Temporal changes in allele frequencies could not be explained by genetic drift or random sampling. Immigration from genetically differentiated populations and a non random mortality induced by Ebola, i.e., selective pressure and cost of sociality, are alternative hypotheses. Understanding the influence of Ebola on gorilla genetic dynamics is of paramount importance for human health, primate evolution and conservation biology

Feeding preference and seed dispersion by Roussetus madagascariensis Grandidier 1928 in North-western Madagascar

Experiments in a flight cage and observations in the field were carried out in North-western Madagascar to study the feeding preference of Rousettus madagascariensis (Family Pteropodidae) between an introduced fruit, jujube (Ziziphus jujuba, Family Rhamnaceae) and an endemic fig (Ficus sakalavarum, Family Moraceae) during the dry season, in May and June 2009. We also investigated quantitative aspects of seed dispersion by R. madagascariensis. Juvenile bats (13) fed intensively on F. sakalavarum, while adults (20) ate both fruit species but with a pronounced preference for unripe Z. jujube fruits. This preference for unripe (immature) fruit, the seeds of which are too large to swallow, suggested that R. madagascariensis does not affect seed dispersal in Z. jujuba. Almost half of the ingested seeds of F. sakalavarum were found in faeces of R. madagascariensis voided during the night in the flight cage, and the remainder was found in regurgitated ‘ejecta’ pellets. Rousettus madagascariensis is thought to be an effective seed disperser of F. sakalavarum, particularly for isolated trees or those in forest fragments where other frugivores are rareDes expériences dans une volière ou cage d'expérimentation et des observations in natura à proximité des arbres ont été réalisées dans la région nord-ouest de Madagascar pour étudier le choix de Rousettus madagascariensis (famille Pteropodidae) entre une espèce de fruit introduite le Jujubier (Ziziphus jujuba, famille Rhamnaceae) et une espèce de figuier endémique (Ficus sakalavarum, famille Moraceae) au cours de la saison sèche. L'aspect quantitatif de la dissémination des graines de cette dernière a également été étudié. Cette étude a été menée en mai et juin 2009. Rousettus madagascariensis utilise les deux espèces, mais la préférence entre les deux fruits varie en fonction de l'âge de l'animal. Les jeunes chauves-souris ont une préférence pour Ficus sakalavarum tandis que les adultes mangent aussi les jujubes qui ne sont généralement pas très mûrs et même si leur graine est trop volumineuse pour être avalée. Nous suggérons que cet animal n'assure pas la dissémination des graines de Z. jujuba. La dissémination des graines par cette espèce pourrait être moins favorable par rapport aux autres animaux qui avalent les graines. Presque la moitié des graines de F sakalavarum a été trouvée dans les fèces de R. madagascariensis laissés pendant la nuit dans la volière, le reste a été recraché sous forme de pelotes de régurgitation. Rousettus madagascariensis participe activement à la dissémination des graines de F. sakalavarum plus particulièrement celles de pieds isolés ou se trouvant dans des fragments d'habitats restreints où les autres animaux disséminateurs sont rares ou absents

Secondary contact and admixture between independently invading populations of the Western corn rootworm, diabrotica virgifera virgifera in Europe

The western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae), is one of the most destructive pests of corn in North America and is currently invading Europe. The two major invasive outbreaks of rootworm in Europe have occurred, in North-West Italy and in Central and South-Eastern Europe. These two outbreaks originated from independent introductions from North America. Secondary contact probably occurred in North Italy between these two outbreaks, in 2008. We used 13 microsatellite markers to conduct a population genetics study, to demonstrate that this geographic contact resulted in a zone of admixture in the Italian region of Veneto. We show that i) genetic variation is greater in the contact zone than in the parental outbreaks; ii) several signs of admixture were detected in some Venetian samples, in a Bayesian analysis of the population structure and in an approximate Bayesian computation analysis of historical scenarios and, finally, iii) allelic frequency clines were observed at microsatellite loci. The contact between the invasive outbreaks in North-West Italy and Central and South-Eastern Europe resulted in a zone of admixture, with particular characteristics. The evolutionary implications of the existence of a zone of admixture in Northern Italy and their possible impact on the invasion success of the western corn rootworm are discussed

Anatomy of a Dansgaard-Oeschger warming transition: High-resolution analysis of the North Greenland Ice Core Project ice core

Large and abrupt temperature oscillations during the last glacial period, known as Dansgaard‐Oeschger (DO) events, are clearly observed in the Greenland ice core record. Here we present a new high‐resolution chemical (2 mm) and stable isotope (20 mm) record from the North Greenland Ice Core Project (NGRIP) ice core at the onset of one of the most prominent DO events of the last glacial, DO‐8, observed ∼38,000 years ago. The unique, subannual‐resolution NGRIP record provides a true sequence of change during a DO warming with detailed annual layer counting of very high depth resolution geochemical measurements used to determine the exact duration of the transition. The continental ions, indicative of long‐range atmospheric loading and dustiness from East Asia, are the first to change, followed by the snow accumulation, the moisture source conditions, and finally the atmospheric temperature in Greenland. The sequence of events shows that atmospheric and oceanic source and circulation changes preceded the DO warming by several years

A horizontal ice core from Taylor Glacier, its implications for Antarctic climate history, and an improved Taylor Dome ice core time scale

Ice core records from Antarctica show mostly synchronous temperature variations during the last deglacial transition, an indication that the climate of the entire continent reacted as one unit to the global changes. However, a record from the Taylor Dome ice core in the Ross Sea sector of East Antarctica has been suggested to show a rapid warming, similar in style and synchronous with the Oldest Dryas—Bølling warming in Greenland. Since publication of the Taylor Dome record, a number of lines of evidence have suggested that this interpretation is incorrect and reflects errors in the underlying time scale. The issues raised regarding the dating of Taylor Dome currently linger unresolved, and the original time scale remains the de facto chronology. We present new water isotope and chemistry data from nearby Taylor Glacier to resolve the confusion surrounding the Taylor Dome time scale. We find that the Taylor Glacier record is incompatible with the original interpretation of the Taylor Dome ice core, showing that the warming in the area was gradual and started at ∼18 ka BP (before 1950) as seen in other East Antarctic ice cores. We build a consistent, up‐to‐date Taylor Dome chronology from 0 to 60 ka BP by combining new and old age markers based on synchronization to other ice core records. The most notable feature of the new TD2015 time scale is a gas age—ice age difference of up to 12,000 years during the Last Glacial Maximum, by far the largest ever observed

Spatially resolving polycyclic aromatic hydrocarbons in Herbig Ae disks with VISIR-NEAR at the VLT

We use the long-slit spectroscopy mode of the VISIR-NEAR experiment to perform diffraction-limited observations of eight nearby Herbig Ae protoplanetary disks. We extract spectra for various locations along the slit with a spectral resolution of R = 300 and perform a compositional fit at each spatial location using spectral templates of silicates and the four PAH bands. This yields the intensity vs. location profiles of each species. Results. We could obtain spatially-resolved intensity profiles of the PAH emission features in the N-band for five objects (AB Aurigae, HD 97048, HD 100546, HD 163296, and HD 169142). We observe two kinds of PAH emission geometry in our sample: centrally-peaked (HD 97048) and ring-like (AB Aurigae, HD 100546, HD 163296, and potentially HD 169142). Comparing the spatial PAH emission profiles with near-infrared scattered light images, we find a strong correlation in the disk sub-structure but a difference in radial intensity decay rate. The PAH emission shows a less steep decline with distance from the star. Finally, we find a correlation between the presence of (sub-) micron-sized silicate grains leading to the depletion of PAH emission within the inner regions of the disks. In this work, we find the following: (1) PAH emission traces the extent of Herbig Ae disks to a considerable radial distance. (2) The correlation between silicate emission within the inner regions of disks and the depletion of PAH emission can result from dust-mixing and PAH coagulation mechanisms and competition over UV photons. (3) For all objects in our sample, PAHs undergo stochastic heating across the entire spatial extent of the disk and are not saturated. (4) The difference in radial intensity decay rates between the PAHs and scattered-light profiles may be attributed to shadowing and dust-settling effects, which affect the scattering grains more than the PAHs