COMPARISON OF THE EFFICIENCY OF PAIR, DUO-TRIO AND TRIANGLE TESTS

The pair, duo-trio and triangle tests were compared, using three levels of instructions with orange drink as medium and sucrose as stimulus. If the subjects know only the nature of the test, the pair test cannot be performed and the frequencies of correct responses above chance of the two other tests do not differ significantly, in this case the triangle test is the more efficient. If the subjects know the nature of the test and the nature of the stimulus, the frequency of correct responses above chance obtained for the pair test is significantly higher than those of the two other tests, in this case the pair test is more efficient. Finally, if the subjects know the nature of the test, the nature of the stimulus and whether or not the sample to be selected contains the stimulus, the conclusions are more difficult to achieve but the triangle test seems to be the more efficient.     

Microsatellite markers reveal two admixed genetic groups and an ongoing displacement within the French population of the invasive plant pathogen Phytophthora infestans

Potato late blight is an example of a re‐emerging disease of plants. Phytophthora infestans was first introduced into Europe during the 19th century, where it caused the Irish potato famine. During the 20th century several additional introduction events have been suspected, especially in the mid‐70s due to the import of large quantities of potato needed after the shortage caused by drought in 1976. Here, we investigate the genetic population structure of Phytophthora infestans, at the first stages of a recent invasion process in France. A total of 220 isolates was collected from 20 commercial fields of the potato susceptible cultivar Bintje, during two consecutive years (2004 and 2005). Clustering analyses based on eight recently developed microsatellite markers reveal that French P. infestans populations are made of two differentiated genetic clusters of isolates (F_ST = 0.19). This result suggests multiple introductions of P. infestans into France, either through the introduction of a composite population of isolates or through the successive introduction of isolates having differentiated genetic backgrounds. Both clusters identified have a strong clonal structure and are similar regarding genetic diversity and mating type composition. The maintenance of differentiation between the two genetic clusters should result from the low or non‐existent contribution of sexual reproduction in French P. infestans populations.     

Patterns of morphological evolution in the mandible of the house mouse Mus musculus (Rodentia: Muridae)

The worldwide distributed house mouse, Mus musculus, is subdivided into at least three lineages, Mus musculus musculus, Mus musculus domesticus, and Mus musculus castaneus. The subspecies occur parapatrically in a region considered to be the cradle of the species in Southern Asia (‘central region’), as well as in the rest of the world (‘peripheral region’). The morphological evolution of this species in a phylogeographical context is studied using a landmark‐based approach on mandible morphology of different populations of the three lineages. The morphological variation increases from central to peripheral regions at the population and subspecific levels, confirming a centrifugal sub‐speciation within this species. Furthermore, the outgroup comparison with sister species suggests that M. musculus musculus and populations of all subspecies inhabiting the Iranian plateau have retained a more ancestral mandible morphology, suggesting that this region may represent one of the relevant places of the origin of the species. Mus musculus castaneus, both from central and peripheral regions, is morphologically the most variable and divergent subspecies. Finally, the results obtained in the present study suggest that the independent evolution to commensalism in the three lineages is not accompanied by a convergence detectable on jaw morphology. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 635–647.     

Dieback and mortality of South African fynbos shrubs is likely driven by a novel pathogen and pathogen‐induced hydraulic failure

We examined whether extensive dry season dieback and mortality in a South African fynbos community were due to drought or pathogen attack. Plant dieback and mortality have been reported elsewhere in similar plant communities suggesting potential for a widespread climatic or biotic threat to this community. We collected tissue samples from Brunia noduliflora, the dominant plant in the community, and cultured them for potential plant pathogens. We also measured dry season predawn and midday water potentials of healthy and stressed plants and constructed pressure‐volume curves to assess turgor loss point. Plant stress and mortality were monitored over a 2‐year study period. Both healthy plants and plants that displayed moderate signs of stress had dry season predawn water potentials well above their turgor loss point suggesting plants were not water stressed. However, plants displaying >60% crown dieback had much lower water potentials (as low as ?12 MPa). A previously undescribed fungus (Pythium sp.) was isolated from the root vascular tissue of all stressed plants and was not present in healthy plants. The proximate cause of plant stress was likely pathogen‐induced, while the ultimate cause of plant death appears to be extreme water stress. The present study suggests that Brunia (Bruniceae), Leucadendron (Proteaceae) and Erica (Ericaceae), all emblematic and dominant genera within the diverse fynbos community, may be susceptible to Pythium infection. This may pose a serious threat to communities already threatened by climate change.     

La Genèse des Mérozoïtes chez la Coccidie Eimeria necatrix. Etude Ultrastructurale*

RESUME. Les schizontes de 2 ème génération d'Eimeria necatrix ont étéétudiés au microscope électronique. La différenciation des mérozoïtes est associée à la dernière mitose, qui ne semble pas différer essentiellement des précédentes. Les mérozoïtes se développent à la périphérie du schizonte. Le conoide et 22 microtubules sous pelliculaires, probablement induits par les centrioles, et le complexe membranaire interne ainsi que les précurseurs des rhoptries, qui semblent issus de l'appareil de Golgi, apparaissent auprès de chaque pôle nucléaire, sous la membrane du schizonte. Ces organites sont les premiers inclus dans les ébauches de mérozoïtes. Puis, le noyau, le dictyosome et les vésicules multimembranaires pénètrent dans les futurs mérozoïtes. Les micronèmes, probablement formés par l'appareil de Golgi, et les grains d'amylopectine sont produits plus tard, quand les mérozoïtes se séparent du reliquat cytoplasmique. Le mode de genèse de ces divers organites et les relations entre le dernière mitose et la différenciation sont discutés. SYNOPSIS. Second generation schizonts of Eimeria necatrix were studied with the aid of the electron microscope. Differentiation of daughter merozoites is associated with the last mitosis, which is not significantly different from the earlier ones. The merozoites develop at the periphery of the schizont. The conoid and 22 subpellicular microtubules, probably induced by centrioles, and the inner membranes complex and the rhoptry anlagen which seem to be produced by the Golgi apparatus, appear close to each nuclear pole, just near the schizont membrane. These organelles are the first to appear in the merozoite anlagen. Then, nucleus, dictyosome and multimembranous vesicles enter the budding merozoites. Micronemes, probably originating from Golgi apparatus, and amylopectin granules are produced later, when daughter merozoites separate from the residuum. The genesis of these various organelles and the relation between the last mitosis and differentiation are discussed.     

Population subdivision and gene flow in Danish house mice

Genetic subdivision in local populations of the European house mice, Mus musculus domesticus and M. m. musculus, was analysed to study patterns of gene flow. The data consisted of frequencies of microsatellite alleles in 16 samples (250 individuals) from a total of 11 sites in Jutland, which included successive samples from three sites. Sequences of the control region of mitochondrial DNA in three successive samples from one site were also analysed. Microsatellite genotype frequencies within samples were close to Hardy-Weinberg expectations. Levels of microsatellite differentiation among samples (θ= 0.05–0.21) corresponded to limited gene flow at migration-drift equilibrium (N_m= 1–5). Weak isolation by distance for microsatellites in M. m. musculus suggested that gene flow tends to occur among neighbouring sites. Estimates of effective population size over a few generations were much lower than those corresponding to the long periods needed for arrival at mutation-drift equilibrium. This suggested that subpopulations had been influenced by gene flow since formation, or had originated recently from genetically diverse founders.