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.     

Spatial variation in abundance of the junin virus hosts in endemic and nonendemic Argentine haemorrhagic fever zones

Abstract Argentine haemorrhagic fever (AHF) is caused by Junin (JUN) virus, which is hosted by the drylands vesper mouse (Calomys musculinus). In this work we monitored population abundance of C. musculinus and rodent assemblages for 3 years in and outside the AHF endemic zones (northern Buenos Aires, southern Córdoba and Santa Fe Provinces, Argentina). The study area was divided into endemic and nonendemic zones. In the endemic zone epidemic sites were recognized, characterized by recent emergence and maintenance of AHF cases, and also historical sites, characterized by decreased incidence or disappearance of AHF human cases. In the nonendemic zone AHF has never been recognized. Although differences were statistically significant only during some periods, population abundance of C. musculinus was usually lower in the nonendemic sites. The pattern and magnitude of seasonal fluctuations in C. musculinus populations were also distinct in the nonendemic sites as compared to endemic sites. The relative abundance of C. musculinus in rodent assemblage was lower in nonendemic sites than in the endemic sites. The lower population densities and dampened seasonal dynamics may be at least partly responsible for the absence of AHF cases in the nonendemic zone. It is suggested that the balance between intra and interspecific interactions might be the cause of the pattern of incidence and prevalence of pathogens in the host species.     

Phylogenetic analysis of Chloraeinae (Orchidaceae) based on plastid and nuclear DNA sequences

The phylogenetic relationships of subtribe Chloraeinae, a group of terrestrial orchids endemic to southern South America, have not been satisfactorily investigated. A previous molecular phylogenetic analysis based on plastid DNA supported the monophyly of Chloraeinae and Gavilea, but showed that Chloraea is non‐monophyletic and that the sole species of Bipinnula analysed is sister to Geoblasta. However, that analysis included only 18 of the 73 species belonging to this subtribe. Here, the phylogenetic relationships of Chloraeinae were assessed by analysing aproximately 7500 bp of nucleotide sequences from nuclear ribosomal internal transcribed spacer (ITS) and plastid DNA (rbcL, matK, trnL‐trnF, rpoB‐trnC) for 42 species representing all four currently accepted genera of Chloraeinae and appropriate outgroups. Nuclear and plastid data were analysed separately and in combination using two different methods, namely parsimony and Bayesian inference. Our analyses support the monophyly of Chloraeinae and their inclusion in an expanded concept of Cranichideae, but none of the genera of Chloraeinae that includes more than one species is monophyletic. Gavilea and Bipinnula are paraphyletic, with Chloraea chica nested in Gavilea and Geoblasta penicillata in Bipinnula. As currently delimited, Chloraea is polyphyletic. The taxonomic changes proposed recently are for the most part not justifiable on phylogenetic grounds, except for recognition of the monotypic genus Correorchis. The lack of resolution for the relationships among species of ‘core’Chloraea suggests a relatively recent diversification of this group. The current generic classification is in need or revision, but additional study is advisable before carrying out further taxonomic changes. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 258–277.     

Correlates and Consequences of Body Size in Nectar-Feeding Birds

Nectar-feeding birds are among the smallest birds and the largestpollinators. Energetic costs of maintenance, temperature regulation,foraging and reproduction increase in direct proportion to bodymass raised to fractional exponents, which may vary from 0.5to 1.0; overall costs probably vary with an exponent of 0.75.Avian nectarivores acquire most of their energy from flowernectar; in so doing they compete with other nectar feeders andpollinate plants. Larger pollinators are more reliable and movepollen greater distances, but to attract them plants must secretemore nectar and protect it from utilization by smaller animals.Minimum body size of avian nectarivores (2g) appears to reflectboth competition with insects and the limited capacity of thesmallest birds to acquire and store energy relative to the demandsof fasting, temperature regulation, and reproduction. Hummingbirdshave attained significantly smaller size than other nectar feedingbirds because lower metabolic rates and use of hypothermic torporreduce their energy expenditure relative to income. Maximumbody size of avian nectarivores (approximately 80g) apparentlyreflects the upper limit of plant energy expenditure for reliable,long distance pollination. Between these limits, size variationreflects divergence to reduce interspecific competition andcoevolution with plants to promote specificity     

The Stigma of Dendrobium speciosum Sm. (Orchidaceae): A New Stigma Type Comprising Detached Cells Within a Mucilaginous Matrix

The stigma of Dendrobium speciosum does not correspond to anymorphological category previously described. The stigma lieson the lower surface of the column as an oval, bowl-shaped depressioncontaining a wet, jelly-like, viscid material, which comprisesa large number of elongated, detached cells suspended in a matrix.The stigmatic cells are thick walled and have a vacuolated cytoplasmcontaining amyloplasts. These cells give a positive reactionto fluorescein diacetate indicating that the plasma membraneis intact; this evidence points to the conclusion that the stigmaticcells are not detached, senescent or necrotic papillae. Histochemical staining of the matrix shows high levels of acidicpolysaccharides with low levels of lipids and proteins. Biochemicalanalysis shows this matrix to comprise around 80 per cent uronicacids. This highly specialized stigma may be a further evolutionarydevelopment of the wet papillate stigma resulting from the specialneeds of both pollination and the nutritional support of thelarge number of developing pollen tubes. Stigma, Dendrobium speciosum, Orchidaceae