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Downy mildews caused by obligate biotrophic oomycetes result in severe crop losses worldwide. Among these pathogens, Pseudoperonospora cubensis and P. humuli, two closely related oomycetes, adversely affect cucurbits and hop, respectively. Discordant hypotheses concerning their taxonomic relationships have been proposed based on host–pathogen interactions and specificity evidence and gene sequences of a few individuals, but population genetics evidence supporting these scenarios is missing. Furthermore, nuclear and mitochondrial regions of both pathogens have been analyzed using microsatellites and phylogenetically informative molecular markers, but extensive comparative population genetics research has not been done. Here, we genotyped 138 current and historical herbarium specimens of those two taxa using microsatellites (SSRs). Our goals were to assess genetic diversity and spatial distribution, to infer the evolutionary history of P. cubensis and P. humuli, and to visualize genome-scale organizational relationship between both pathogens. High genetic diversity, modest gene flow, and presence of population structure, particularly in P. cubensis, were observed. When tested for cross-amplification, 20 out of 27 P. cubensis-derived gSSRs cross-amplified DNA of P. humuli individuals, but few amplified DNA of downy mildew pathogens from related genera. Collectively, our analyses provided a definite argument for the hypothesis that both pathogens are distinct species, and suggested further speciation in the P. cubensis complex.
The taxonomy of cyclostome bryozoans is founded on characters of the skeleton, but molecular sequence data have increasingly shown that established higher taxa are not monophyletic. Here we describe the skeletal morphology of a new species from Guadeloupe (French West Indies) with erect ramose colonies consisting of long, curved zooids that are typical of the suborder Cerioporina among living cyclostomes. However, molecular evidence from nuclear ribosomal RNA genes 18S and 28S places the new taxon in the suborder Rectangulata, where this colony-form has not been previously recorded. It nests firmly within the genus Disporella Gray, 1848, in a strongly supported clade that also includes Plagioecia patina (Lamarck, 1816) (Tubuliporina) and the sister taxa Doliocoitis cyanea Gordon & Taylor, 2001 (Rectangulata) and Favosipora rosea Gordon & Taylor, 2001 (Cerioporina). The short and robust branches of the new Guadeloupe cyclostome, here named Disporella guada Harmelin, Taylor & Waeschenbach sp. nov., are well adapted to life in shallow rocky sites exposed to severe wave action, which appear to be its exclusive habitat.
A new family, Electrocambalidae fam. nov. of the suborder Cambalidea is described from Cretaceous Burmese amber based on two new genera, Electrocambala gen. nov. and Kachincambala gen. nov. with four new species, Electrocambala ornata gen. et sp. nov., E. cretacea gen. et sp. nov., Kachincambala muelleri gen. et sp. nov. and K. distorta gen. et sp. nov. The specimens are described combining classical light microscopy with drawings and photography, and modern micro-computed tomography (μCT). Morphological characters otherwise obscured are examined and visualized by creating volume renderings and 3D-segmentations from μCT data. Electrocambalidae fam. nov. is characterized by the following character combination: (1) a forward shift of leg pair 3, resulting in an apparently legless 3rd body ring, (2) presence of metazonital setae, and (3) extensive pilosity on the head. Although some of these characters are shared with other Juliformia they are unique in this combination. The described fossils are the oldest and first Mesozoic Spirostreptida and Cambalidea known and ca 70 million years older than previous records of the group.