Traditional morphology-based taxonomy of dictyostelids is rejected by molecular phylogeny. A new classification is presented based on monophyletic entities with consistent and strong molecular phylogenetic support and that are, as far as possible, morphologically recognizable. All newly named clades are diagnosed with small subunit ribosomal RNA (18S rRNA) sequence signatures plus morphological synapomorphies where possible. The two major molecular clades are given the rank of order, as Acytosteliales ord. nov. and Dictyosteliales. The two major clades within each of these orders are recognized and given the rank of family as, respectively, Acytosteliaceae and Cavenderiaceae fam. nov. in Acytosteliales, and Dictyosteliaceae and Raperosteliaceae fam. nov. in Dictyosteliales. Twelve genera are recognized: Cavenderia gen. nov. in Cavenderiaceae, Acytostelium, Rostrostelium gen. nov. and Heterostelium gen. nov. in Acytosteliaceae, Tieghemostelium gen. nov., Hagiwaraea gen. nov., Raperostelium gen. nov. and Speleostelium gen. nov. in Raperosteliaceae, and Dictyostelium and Polysphondylium in Dictyosteliaceae. The "polycephalum" complex is treated as Coremiostelium gen. nov. (not assigned to family) and the "polycarpum" complex as Synstelium gen. nov. (not assigned to order and family). Coenonia, which may not be a dictyostelid, is treated as a genus incertae sedis. Eighty-eight new combinations are made at species and variety level, and Dictyostelium ammophilum is validated.

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BackgroundSocial Amoebae or Dictyostelia are eukaryotic microbes with a unique life cycle consisting of both uni- and multicellular stages. They have long fascinated molecular, developmental and evolutionary biologists, and Dictyostelium discoideum is now one of the most widely studied eukaryotic microbial models. The first molecular phylogeny of Dictyostelia included most of the species known at the time and suggested an extremely deep taxon with a molecular depth roughly equivalent to Metazoa. The group was also shown to consist of four major clades, none of which correspond to traditional genera. Potential morphological justification was identified for three of the four major groups, on the basis of which tentative names were assigned.ResultsOver the past four years, the Mycetozoan Global Biodiversity Survey has identified many new isolates that appear to be new species of Dictyostelia, along with numerous isolates of previously described species. We have determined 18S ribosomal RNA gene sequences for all of these new isolates. Phylogenetic analyses of these data show at least 50 new species, and these arise from throughout the dictyostelid tree breaking up many previously isolated long branches. The resulting tree now shows eight well-supported major groups instead of the original four. The new species also expand the known morphological diversity of the previously established four major groups, violating nearly all previously suggested deep morphological patterns.ConclusionsA greatly expanded phylogeny of Dictyostelia now shows even greater morphological plasticity at deep taxonomic levels. In fact, there now seem to be no obvious deep evolutionary trends across the group. However at a finer level, patterns in morphological character evolution are beginning to emerge. These results also suggest that there is a far greater diversity of Dictyostelia yet to be discovered, including novel morphologies.

The future existence of common ash (Fraxinus excelsior), an important tree species throughout temperate Europe, is threatened. An invasive fungal disease (ash dieback) has spread through much of the distribution area of common ash. The causal agent of the disease is Hymenoscyphus fraxineus, a necrotrophic ascomycete, most probably introduced from Asia in the early 1990s. Hymenoscyphus fraxineus infects ash trees and saplings through their leaves, from which it grows into the stem. The fungus was studied intensively in recent years but there is still a need to address the topic from an evolutionary perspective. In this overview, some key evolutionary aspects of ash dieback are discussed, from the Red Queen dynamics of host–pathogen interactions to the probable consequences for virulence evolution of multiple infections. The progression of ash dieback in Europe does not show spatial differences, but studies show variation in susceptibility within host populations, a probable consequence of genetic differences, thus providing material for evolution of disease resistance or tolerance. Breeding programmes need to maintain the genetic diversity of Fraxinus, to enable it to withstand further threats such as climate change and the emerald ash borer. Because H. fraxineus reproduces exclusively sexually, the pathogen is likely to overcome a narrow genetic resistance. The introduction of further strains of H. fraxineus to Europe and the movement of infected plant material should be avoided. This case study shows that the integration of evolutionary ecology considerations would benefit plant disease management and biosecurity in general.

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org. This content downloaded from 137.120.4.50 on Sat, 02 Jan 2016 20:57:58 UTC All use subject to JSTOR Terms and Conditions REVIEWS AND COMMENTS REVIEWS AND COMMENTS REVIEWS AND COMMENTS REVIEWS AND COMMENTSIn examining this monograph, I am again struck with regret that this beautiful analysis of a single specimen of a rare animal lacks any companion volumes containing equally careful morphological descriptions of more common turtles, for which adequate series of different growth stages would pose fewer curatorial and logistic problems.-CARL GANS, West Sylvania Ave., Neptune, New Jersey 07753. 224 pp., 108 illus., paperback, $12.95.-This is a well organized, clearly written review of fish parasite control and treatment methods. The authors, who are renowned specialists in the field, have drawn together more than 390 up-to-date references and over 440 treatments. The treatments are discussed for each major parasite group in a handy chart form that greatly facilitates the book's usefulness. Interspersed between the charts are full-page or half-page color plates illustrating the parasites and the appearance of their infections in fish. There are 108 illustrations (all but 2 in color) on 57 pages, constituting more than 25% of the book's length and resulting in a significantly higher than expected price for a paperback. The authors, by their own admission, made no attempt to evaluate the various works cited or to provide a systematic means for the reader to determine the identification of the specific pathogen involved. They do, however, cite major references that deal with diagnosis of the pathogen or comprehensively discuss treatment and control methods.Knowledge in the area of fish parasites and infectious diseases has been constantly growing ever since shortly after the turn of the century. Early pioneers like H. S. Davis, who eventually founded what is now known as the U. S. Dept. of Interior's Eastern Fish Disease Laboratory, laid the groundwork for subsequent development by investigators such as Fish, Gutsell, Rucker, Snieszko and Wolf. Yet, no matter how impressive the body of information has grown it has never kept pace or satisfied the demands from the many state and federal fish hatcheries, and especially in more recent years with those of the rapidly expanding aquarium In examining this monograph, I am again struck with regret that this beautiful analysis of a single specimen of a rare animal lacks any companion volumes containing equally careful morphological descriptions of more common turtles, for which adequate series of different growth stages would pose fewer curatorial and logistic problems.-CARL GANS,

During the period of February to April of 1998, soil/litter samples for isolation of dictyostelid cellular slime moulds were collected throughout New Zealand. Collecting sites included examples of main forest types found in the country and a range in latitude (35°S to 47°S) that encompassed most of New Zealand. Thirteen species of dictyostelids were recovered; all of these occurred at low frequencies and densities. This total included a number of species (e.g., Dictyostelium mucoroides and Polysphondylium violaceum) that are common and widespread throughout the Northern Hemisphere as well as several other species that have a more restricted distribution. Among the latter are Dictyostelium fasciculatum, not previously known outside of Europe, and D. rosarium, previously reported from only a few scattered localities in the Northern Hemisphere. Five of the species recovered (D. antarcticum, D. australe, D. leptosomum, D. quercibrachium, and P. anisocaule) are described for the first time. New Zealand is the most isolated land mass of its size in the world, and the assemblage of dictyostelids present is quite distinctive and seems to reflect this isolation.