Frederick W. Spiegel

The New Higher Level Classification of Eukaryotes with Emphasis on the Taxonomy of Protists

Abstract. This revision of the classification of unicellular eukaryotes updates that of Levine et al. (1980) for the protozoa and expands it to include other protists. Whereas the previous revision was primarily to incorporate the results of ultrastructural studies, this revision incorporates results from both ultrastructural research since 1980 and molecular phylogenetic studies. We propose a scheme that is based on nameless ranked systematics. The vocabulary of the taxonomy is updated, particularly to clarify the naming of groups that have been repositioned. We recognize six clusters of eukaryotes that may represent the basic groupings similar to traditional “kingdoms.” The multicellular lineages emerged from within monophyletic protist lineages: animals and fungi from Opisthokonta, plants from Archaeplastida, and brown algae from Stramenopiles.

The revised classification of eukaryotes.

This revision of the classification of eukaryotes, which updates that of Adl et al. [J. Eukaryot. Microbiol. 52 (2005) 399], retains an emphasis on the protists and incorporates changes since 2005 that have resolved nodes and branches in phylogenetic trees. Whereas the previous revision was successful in re‐introducing name stability to the classification, this revision provides a classification for lineages that were then still unresolved. The supergroups have withstood phylogenetic hypothesis testing with some modifications, but despite some progress, problematic nodes at the base of the eukaryotic tree still remain to be statistically resolved. Looking forward, subsequent transformations to our understanding of the diversity of life will be from the discovery of novel lineages in previously under‐sampled areas and from environmental genomic information.

Diversity, Nomenclature, and Taxonomy of Protists

the origin of echolocation and flight in bats. Nature 403:188– 192. van Rheede, T., T. Bastiaans, D. N. Boone, S. B. Hedges, W. W. de Jong, and O. Madsen. 2006. The platypus in its place: nuclear genes and indels confirm the sister group relation of monotremes and therians. Mol. Biol. Evol. 23:587–597. Waddell, P. J., H. Kishino, and R. Ota. 2001. A phylogenetic foundation for comparative mammalian genomics. Genome Informatics 12:141– 154. Waddell, P. J., N. Okada, and M. Hasegawa. 1999. Towards resolving the interordinal relationships of placental mammals. Syst. Biol. 48:1–5. Waddell, P. J., and S. Shelley. 2003. Evaluating placental inter-ordinal phylogenies with novel sequences including RAG1, γ -fibrinogen, ND6, and mt-tRNA, plus MCMC-driven nucleotide, amino acid, and codon models. Mol. Phylogenet. Evol. 28:197–224.

Phylogeny of the “Forgotten” Cellular Slime Mold, Fonticula alba, Reveals a Key Evolutionary Branch within Opisthokonta

The shared ancestry between Fungi and animals has been unequivocally demonstrated by abundant molecular and morphological data for well over a decade. Along with the animals and Fungi, multiple protists have been placed in the supergroup Opisthokonta making it exceptionally diverse. In an effort to place the cellular slime mold Fonticula alba, an amoeboid protist with aggregative, multicellular fruiting, we sequenced five nuclear encoded genes; small subunit ribosomal RNA, actin, beta-tubulin, elongation factor 1-alpha, and the cytosolic isoform of heat shock protein 70 for phylogenetic analyses. Molecular trees demonstrate that Fonticula is an opisthokont that branches sister to filose amoebae in the genus Nuclearia. Fonticula plus Nuclearia are sister to Fungi. We propose a new name for this well-supported clade, Nucletmycea, incorporating Nuclearia, Fonticula, and Fungi. Fonticula represents the first example of a cellular slime mold morphology within Opisthokonta. Thus, there are four types of multicellularity in the supergroup-animal, fungal, colonial, and now aggregative. Our data indicate that multicellularity in Fonticula evolved independent of that found in the fungal and animal radiations. With the rapidly expanding sequence and genomic data becoming available from many opisthokont lineages, Fonticula may be fundamental to understanding opisthokont evolution as well as any possible commonalities involved with the evolution of multicellularity.

Eumycetozoa = Amoebozoa?: SSUrDNA Phylogeny of Protosteloid Slime Molds and Its Significance for the Amoebozoan Supergroup

Amoebae that make fruiting bodies consisting of a stalk and spores and classified as closely related to the myxogastrids have classically been placed in the taxon Eumycetozoa. Traditionally, there are three groups comprising Eumycetozoa: myxogastrids, dictyostelids, and the so-called protostelids. Dictyostelids and myxogastrids both make multicellular fruiting bodies that may contain hundreds of spores. Protostelids are those amoebae that make simple fruiting bodies consisting of a stalk and one or a few spores. Protostelid-like organisms have been suggested as the progenitors of the myxogastrids and dictyostelids, and they have been used to formulate hypotheses on the evolution of fruiting within the group. Molecular phylogenies have been published for both myxogastrids and dictyostelids, but little molecular phylogenetic work has been done on the protostelids. Here we provide phylogenetic trees based on the small subunit ribosomal RNA gene (SSU) that include 21 protostelids along with publicly available sequences from a wide variety of amoebae and other eukaryotes. SSU trees recover seven well supported clades that contain protostelids but do not appear to be specifically related to one another and are often interspersed among established groups of amoebae that have never been reported to fruit. In fact, we show that at least two taxa unambiguously belong to amoebozoan lineages where fruiting has never been reported. These analyses indicate that we can reject a monophyletic Eumycetozoa, s.l. For this reason, we will hereafter refer to those slime molds with simple fruiting as protosteloid amoebae and/or protosteloid slime molds, not as protostelids. These results add to our understanding of amoebozoan biodiversity, and demonstrate that the paradigms for understanding both nonfruiting and sporulating amoebae must be integrated. Finally, we suggest strategies for future research on protosteloid amoebae and nonfruiting amoebae, and discuss the impact of this work for taxonomists and phylogenomicists.

Phylogenetic significance of the flagellar apparatus in protostelids (eumycetozoa)

The ultrastructure of the flagellar apparatuses of four species of protostelids is described. All four species have the same three major groups of rootlet microtubules in common, microtubule arrays (MTA) 2, 3, and 4. Variation is found in the number of centrioles per flagellar apparatus, presence or absence of two other microtubule arrays, MTA 1 and MTA 5, types of connectives linking the centrioles to the MTAs, nature of the transitional elements of the flagella, and the association of the flagellar apparatus with the nucleus. It is concluded on the basis of this study and comparison with earlier studies on protostelids, myxomycetes, and other amoeboflagellates that the flagellate species of protostelids are monophyletic. The significance of this to the phylogeny of protostelids and related mycetozoans is discussed.

Evidence for mating between islates of Colletotrichum gloeosporioides with different host specificities

Individual isolates of the ibiquitous plant pathogen Colletotrichum gloeosporioides (teleomorph Glomerella cingulata) can have very restricted host ranges. Isolates that share the same host range are considered to be genetically discrete units, and sexual compatibility has been reported to be limited to individuals that share the same host range. However, we have recently observed that some isolates of C. gloeosporioides that are specifically pathogenic to different, distantly-related hosts are sexually compatible. Ascospore progeny from one such cross were randomly isolated and outcrossing was verified by the reassortment of several RFLP markers among the progeny. In addition, the progeny were analyzed for pathogenicity to parental hosts. The implications of sexual compatibility between C. gloeosporioides isolates with different host specificities on the evolution of Colletotrichum species are discussed.

Amoeba at Attention: Phylogenetic Affinity of Sappinia pedata

ABSTRACT. The genus Sappinia, a taxon of free‐living amoebae with trophozoites that typically have two closely appressed nuclei, contains two named species, Sappinia pedata, the type species, and S. diploidea. The amoebae of both species are essentially identical according to the literature. The two species are distinguished by S. pedata having a standing amoeba stage, incorrectly interpreted as a cyst, and S. diploidea having sessile, bicellular cysts. Using four isolates of S. pedata collected from around the world, we present detailed light micrographic illustrations of all stages of its life cycle. We confirm that the standing amoeba lacks a cell wall. In two isolates of S. pedata, there are bicellular cysts indistinguishable from those of S. diploidea. Using sequence data from the nuclear small subunit ribosomal RNA gene, we conclude that S. pedata and the published neotype of S. diploidea are congeneric but not conspecific. The genus branches within Thecamoebidae. Sequencing of the actin gene confirms the inclusion of Sappinia in Thecamoebidae. Resolving the taxonomy of Sappinia is gaining importance because it has recently been attributed as an opportunistic human pathogen.

A NEW TECHNIQUE FOR SAMPLING PROTOSTELIDS

A new technique has been designed to col- lect protostelids repeatedly on a standardized sub? strate that has been introduced into a habitat known to contain an assemblage of species of protostelids. Four species of protostelids were detected after 1 week of placing sterilized wheat straw into a leaf litter hab? itat. After 8 weeks, a total of eight species were found. All of these species were also present on samples of litter taken from the same site. Moreover, at least one species of protostelid fruited on 75 of the 80 straws examined. The most common species detected were Nematostelium ovatum, N. gracile, and Schizoplasmodiop? sis pseudoendospora. These species also appear most frequently when plating leaf litter from this site. This technique has potential use in the study of protostelid ecology.

Between a Pod and a Hard Test: The Deep Evolution of Amoebae

Abstract Amoebozoa is the eukaryotic supergroup sister to Obazoa, the lineage that contains the animals and Fungi, as well as their protistan relatives, and the breviate and apusomonad flagellates. Amoebozoa is extraordinarily diverse, encompassing important model organisms and significant pathogens. Although amoebozoans are integral to global nutrient cycles and present in nearly all environments, they remain vastly understudied. We present a robust phylogeny of Amoebozoa based on broad representative set of taxa in a phylogenomic framework (325 genes). By sampling 61 taxa using culture-based and single-cell transcriptomics, our analyses show two major clades of Amoebozoa, Discosea, and Tevosa. This phylogeny refutes previous studies in major respects. Our results support the hypothesis that the last common ancestor of Amoebozoa was sexual and flagellated, it also may have had the ability to disperse propagules from a sporocarp-type fruiting body. Overall, the main macroevolutionary patterns in Amoebozoa appear to result from the parallel losses of homologous characters of a multiphase life cycle that included flagella, sex, and sporocarps rather than independent acquisition of convergent features.