Five new species of dictyostelid social amoebae (Amoebozoa) from Thailand.

BACKGROUND: Dictyostelid cellular slime molds (dictyostelids) are common inhabitants of the soil and leaf litter layer of fields and forests, along with animal dung, where they feed mostly on bacteria. However, reports on the species diversity of dictyostelids in South Asia, particularly Thailand, are limited. The research reported in this paper was carried out to increase our knowledge of the species diversity of this group of organisms in northern Thailand. RESULTS: Forty soil samples were collected at four localities in northern Thailand to assess the species richness of dictyostelids. These samples yielded five dictyostelid isolates that were not morphologically consistent with any described species. Based on molecular signatures, all five of these isolates were assigned to the family Cavenderiaceae, genus Cavenderia. All five share a number of morphological similarities with other known species from this family. The new taxa differ from previously described species primarily in the size and complexity of their fruiting bodies (sorocarps). This paper describes these new species (Cavenderia aureostabilis, C. bhumiboliana, C. protodigitata, C. pseudoaureostipes, and C. subdiscoidea) based on a combination of morphological characteristics and their phylogenetic positions. CONCLUSIONS: At least 15 taxa of dictyostelids were obtained from the four localities in northern Thailand, which indicates the high level of species diversity in this region. Five species were found to be new to science. These belong to the family Cavenderiaceae, genus Cavenderia, and were described based on both morphology and phylogeny.

New species of Polysphondylium from Madagascar.

Two series of samples collected for isolation of dictyostelid cellular slime molds (dictyostelids) in Madagascar yielded a relatively large number of isolates of Polysphondylium. Most of these turned out to be species new to science that show varying degrees of clustering from unclustered to coremiform as well as an ability to migrate. Migratory ability (phototaxis) is a common feature of species assigned to Group 2 of the Polysphondylia and is common in the new species from Madagascar. Another common feature, clustering, appears to be a strategy for keeping fruiting bodies erect for a longer time in a climate that is relatively dry, whereas migratory ability may function seasonally when there is more rainfall. Thirteen species are described herein. Each of these is characterized by a particular set of distinguishing features, and collectively they expand our concept of the genus Polysphondylium.

New small dictyostelids from seasonal rainforests of Central America.

Ten small dictyostelids isolated from samples collected from the surface humus layer of seasonal rainforests of Belize and Guatemala were studied morphologically, and nine were found to represent distinct species, all with an average height of < 2 mm (0.5-3.5 mm). Although their fruiting bodies (sorocarps) closely resemble one another, the nine species differ in their patterns of aggregation, stream pattern, branching development, formation of microcysts, spore shape, presence or absence of spore granules and their distribution, as well as in the shapes and behavior of their sorogens and myxamoebae. These stable morphological features were sufficient to recognize nine new species of small dictyostelids, one with two varieties. SSU rDNA sequences were generated for all these new isolates, and phylogenetic analyses of these sequences show these new isolates belong to Dictyostelid group 3. As a result of this and other recent studies, the concept of what constitutes a species in the dictyostelids has become much more restricted and well defined, in as much as some of the morphological and behavioral patterns now being observed were overlooked in the past. The extent, flow direction and conformation of streaming within the group varies from simple aggregation mounds with no streams to short streams, to somewhat longer streams and finally to well developed streams. Each of these is characterized by a particular set of distinguishing features.

Four New Species of Dictyostelids from Soil Systems in Northern Thailand.

Dictyostelid cellular slime molds (dictyostelids) are ubiquitous microorganisms found in the uppermost layers of most soils. Reports on the species diversity of dictyostelids in Southeast Asia, particularly Thailand, are few in number. A survey for dictyostelids performed in northern Thailand in 2008 recovered 15 distinctive forms, including several common species and a number of forms morphologically different from anything already described. Five of the latter were formally described as new to science in a previous paper. An additional five isolates appeared to be morphologically distinct, and this was supported by DNA sequence data and phylogenetic analysis. These isolates representing four species are described herein as species new to science. Detailed descriptions and illustrations of these new species are provided.

An expanded phylogeny of social amoebas (Dictyostelia) shows increasing diversity and new morphological patterns.

BACKGROUND: Social 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. RESULTS: Over 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. CONCLUSIONS: A 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.

Dictyostelid cellular slime molds associated with grasslands of the central and western United States.

Dictyostelid cellular slime molds (dictyostelids) associated with grassland ecosystems of the central and western United States were investigated at nine sites that included examples of the three major ecological types of grasslands (tall grass, mixed grass and short grass) generally recognized for the region. Samples of soil/humus collected from each site were examined with the Cavender method of isolating dictyostelids. For each of those six sites with well developed gallery forests present, an additional set of forest soil/humus samples was collected. A more intensive sampling effort was carried out at one site (Konza LTER) to assess the possible effects of burning and grazing on dictyostelid diversity and density. Twelve species of dictyostelids were recovered from grassland sites, whereas gallery forest sites yielded only nine species. Four cosmopolitan species (Dictyostelium giganteum, D. mucoroides, D. sphaerocephalum and Polysphondylium pallidum) were represented by the greatest densities of clones, with D. sphaerocephalum particularly common. The general pattern across all sites was that both species richness and density of dictyostelids decreased with decreasing precipitation. Samples collected from ungrazed grassland plots yielded higher numbers of both species and clones as compared to grazed plots, and the general pattern was for both values to increase as the interval between fires increased. For numbers of clones this correlation was statistically significant.

Two new species of dictyostelid cellular slime molds from Alaska.

In sampling soils to survey dictyostelid cellular slime molds in Alaska we encountered two groups of isolates that have morphologies that differ from any previously described species within their group. We sequenced the nuclear small subunit ribosomal RNA gene (SSU rDNA) of selected isolates from the two groups and found sequences from both groups to be distinct from all previously described dictyostelid sequences. Phylogenetic analyses place one novel species in dictyostelid Group 2 and the other in Group 4 (Schaap et al. 2006). In this paper we formally describe as new these two species of cellular slime molds, Dictyostelium ammophilum sp. nov. and Dictyostelium boreale sp. nov., based on the combination of morphological and molecular characters.

Additional new species suggest high dictyostelid diversity on Madagascar.

Dictyostelids are a monophyletic group of sorocarp-forming social amoebae in the major eukaryotic division Amoebozoa. Members of this taxon, which is made up of almost 200 described species, are common in terrestrial soils globally. Still, the alpha diversity is not well known in many areas, and new species are frequently recovered. The highest species richness is found in the tropics. Here, five new species are described from soil samples collected in Madagascar. These species-Cavenderia basinodulosa, C. canoespora, Heterostelium radiatum, H. versatile, and Raperostelium stabile-are described based on both morphological characteristics and molecular data, with sequence data from the rDNA small subunit (SSU). The five new species are morphologically disparate, ranging from relatively small, robust taxa such as R. stabile to taxa with variable morphologies such as the larger H. radiatum and H. versatile and the yellow-tinted and irregularly branched species C. canoespora and C. basinulosa. These new species, together with earlier work where 13 other species were described from the island, suggest that there is a range of genetically diverse and highly morphologically variable dictyostelid taxa occurring on Madagascar, suggesting biogeographic patterns even within these very small organisms.

A New Classification of the Dictyostelids.

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.

Distribution and ecology of dictyostelid cellular slime molds in Great Smoky Mountains National Park.

Great Smoky Mountains National Park encompasses an area of 2080 km2 in eastern Tennessee and western North Carolina between 35 degrees 28' and 35 degrees 47' N. Elevations are 270-2000 m above sea level, and the topography and vegetation are as diverse as any region of eastern North America. In 1998-2004 soil/litter samples for isolation of dictyostelid cellular slime molds were collected throughout the park. Collecting sites included examples of all major forest types along with the more common types of nonforest vegetation. More than 2300 clones of dictyostelids were recovered from 412 samples. These clones included representatives of 20 described species together with at least 10 species new to science. This total is higher than those reported for other temperate regions of the world. In general both numbers of species and numbers of clones/g of sample material decreased with increasing elevation and several species displayed a distinct preference for either the low or high end of the elevation gradient. The relatively high number of new species recovered from samples collected at high elevations is an important new finding for dictyostelid ecology and distribution.

New species of small dictyostelids from the Great Smoky Mountains National Park.

Ten new species of small dictyostelids, five belonging to Acytostelium (A. anastomosans, A. longisorophorum, A. magnisorum, A. serpentarium and A. singulare) and five to Dictyostelium (D. amphisporum, D. naviculare, D. oculare, D. potamoides and D. stellatum), were isolated from forest soils in the Great Smoky Mountains National Park. These species were recovered mostly from acidic soils and at higher elevations. They represent a large group of dictyostelids of small stature (<2 mm total height) on which we are beginning to accumulate more information.

The effects of dictyostelids on the formation and maturation of myxomycete plasmodia.

Dictyostelids (cellular slime molds) and myxomycetes (plasmodial slime molds) are two groups of mycetozoans usually present and often abundant in the soil and litter microhabitats of terrestrial ecosystems. Because they utilize the same food resource and occur together in a spatially limited and clearly defined microhabitat, the potential for ecological interactions would seem to exist. However, relatively few previous studies have considered this aspect of mycetozoan ecology. In the present study twenty-eight isolates (8 species) of dictyostelids were co-cultured in all possible pair-wise combinations with fourteen isolates (7 species) of myxomycetes to determine if there were any effects on the production of fruiting bodies. Dictyostelids showed little or no delay in culmination and only random and inconsistent reductions in sorocarp abundance when co-cultured with myxomycetes. In contrast, myxomycetes displayed a number of specific effects. The heterothallic isolates exhibited delays in plasmodial formation and/or maturation, with some pairings showing little to no effect, while others displayed nearly complete inhibition of plasmodial formation or maturation. Apomictic isolates, in general, were much less affected, with only a few combinations displaying significant delays in both formation and maturation of plasmodia.