James C. Cavender

Geographical distribution of Acrasieae

The frequency of occurrence of Acrasieae was determined in 28 temperate and tropical countries on five continents. Twenty-nine different cellular slime molds, including five new to science, were is...

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

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.

Genetic Heterogeneity in Wild Isolates of Cellular Slime Mold Social Groups

This study addresses the issues of spatial distribution, dispersal, and genetic heterogeneity in social groups of the cellular slime molds (CSMs). The CSMs are soil amoebae with an unusual life cycle that consists of alternating solitary and social phases. Because the social phase involves division of labor with what appears to be an extreme form of “altruism”, the CSMs raise interesting evolutionary questions regarding the origin and maintenance of sociality. Knowledge of the genetic structure of social groups in the wild is necessary for answering these questions. We confirm that CSMs are widespread in undisturbed forest soil from South India. They are dispersed over long distances via the dung of a variety of large mammals. Consistent with this mode of dispersal, most social groups in the two species examined for detailed study, Dictyostelium giganteum and Dictyostelium purpureum, are multi-clonal.

Dictyostelid cellular slime moulds in the forests of New Zealand

Abstract 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.

Taxonomy, slime molds, and the questions we ask.

Taxonomic treatments often influence the way we both ask and attempt to answer certain biological questions. The classical taxonomy of the dictyostelid cellular slime molds (Dictyosteliales) involves a convenient set of categories that were developed independent of phylogeny. In order to test whether the characters supporting the classical taxonomy hold any phylogenetic signal, we subjected 19 described taxa belonging to two families (Acytosteliaceae and Dictyosteliaceae) and three genera (Acytostelium, Dictyostelium, and Polysphondylium) to rooted cladistic analyses using PAUP* v 4.0b4a. Neither family nor any of the three genera were found to represent monophyletic groups. These results confirm that the classical taxonomy used to delineate families and genera within these slime molds carries very little phylogenetic signal. Taxonomic character sets should be scrutinized phylogenetically in order to determine what information they provide about the relatedness of taxa within a group. Because taxonomy often drives the nature of biological inquiry, caution should be exercised when drawing conclusions regarding the evolution of developmental systems in Dictyostelium.

CELLULAR SLIME MOLDS OF JAPAN. I. DISTRIBUTION AND BIOGEOGRAPHICAL CONSIDERATIONS

Dictyostelid slime molds were isolated from forest soils of the three main islands of Japan, Honshu, Shikoku and Hokkaido. Twenty-six species were recovered, including three undescribed. Dictyostel...

Cellular slime molds of the Rocky Mountains

Soil populations of cellular slime molds (CSM) are generally smaller and less diverse in soils of Rocky Mountain forests than in eastern deciduous forests. CSM were found at all elevations and habitats sampled, including desert scrub, pinyon-juniper, ponderosa pine, spruce-fir and tundra. Of these, which exist along an altitudinal gradient, the subalpine sprucefir belt, the most humid of the forest belts in this relatively dry region, had the largest and most diverse populations. Almost all sites were dominated by Dictyostelium mucoroides and D. sphaerocephalum. Since Rocky Mountain soils are exposed to severe environmental fluctuations these two species are the most tolerant of the dictyostelids, particularly to moisture and temperature stresses. Dictyostelium septentrionalis was the only rare species discovered.

Cellular Slime Molds of the Southern Appalachians

The occurrence and distribution of cellular slime molds were studied in relation to altitude of Southern Appalachian forest sites. Nineteen sites were sampled in seven forest types at elevations between 230 and 1,800 m. The diversity of cellular slime molds was greater than in other geographical areas of temperate North America. Twelve described dictyostelid slime molds and one acrasid slime mold were isolated in addition to a new species of the genus Polysphondylium, and a naturally occurring mutant of uncertain affinity. One species, Acytostelium subglobosum, was isolated for the first time in North America. Optimum forest habitats in terms of acrasian diversity were between 590 and 820 m. Segregation of species by altitude was similar to that by latitude, again indicating a strong climatic influence on distribution.

New species of dictyostelids from Patagonia and Tierra del Fuego, Argentina

In late Jan and early Feb 2005 samples for isolation of dictyostelid cellular slime molds (dictyostelids) were collected in five different provinces and from six national parks (all located 39–55°S) in Patagonia and Tierra del Fuego, Argentina. Southern beech (Nothofagus) forests represented the primary vegetation type investigated, but some samples were obtained from Patagonian steppe, alpine meadows, Valdivian temperate rainforests and coniferous forests dominated by Araucaria, Austrocedrus and Fitzroya. Among the dictyostelids isolated from the samples we collected were seven species new to science. These species (Dictyostelium austroandinum, D. chordatum, D. fasciculoideum, D. gargantuum, D. leptosomopsis, D. valdivianum and Polysphondylium patagonicum) are described herein on the basis of both morphology and molecular (SSU rDNA) data. One of the new species, D. gargantuum, is one of the largest representatives of the group reported to date. Another unusual species, D. chordatum, produces long interwoven sorocarps that do not appear to respond to a spacing gas similar to the condition first noted in D. implicatum.

A new species of cellular slime mold from southern Portugal based on morphology, ITS and SSU sequences

Sampling soils to look for dictyostelids in southern Portugal we found an isolate that has a morphology that differed from any previously described species of the group. We sequenced the internally transcribed spacer (ITS) and small subunit (SSU) genes of the nuclear ribosomal RNA and found that both sequences are distinct from all previously described sequences. Phylogenetic analyses place the new species in dictyostelid Group 3 (Rhizostelids) together with D. potamoides, with which it shares 65.8% identity for ITS and 96.6% for SSU. In this paper we describe a new species of cellular slime mold, Dictyostelium ibericum, based on morphological and molecular characters. It is a small species with polar granules in its spores.