Ichthyosporea: a window into the origin of animals.

Ichthyosporea is an underexplored group of unicellular eukaryotes closely related to animals. Thanks to their phylogenetic position, genomic content, and development through a multinucleate coenocyte reminiscent of some animal embryos, the members of Ichthyosporea are being increasingly recognized as pivotal to the study of animal origins. We delve into the existing knowledge of Ichthyosporea, identify existing gaps and discuss their life cycles, genomic insights, development, and potential to be model organisms.

Current ecological understanding of fungal-like pathogens of fish: what lies beneath?

Despite increasingly sophisticated microbiological techniques, and long after the first discovery of microbes, basic knowledge is still lacking to fully appreciate the ecological importance of microbial parasites in fish. This is likely due to the nature of their habitats as many species of fish suffer from living beneath turbid water away from easy recording. However, fishes represent key ecosystem services for millions of people around the world and the absence of a functional ecological understanding of viruses, prokaryotes, and small eukaryotes in the maintenance of fish populations and of their diversity represents an inherent barrier to aquatic conservation and food security.

Comparative morphology and genealogical delimitation of cryptic species of sympatric isolates of Sphaeroforma (Ichthyosporea, Opisthokonta).

Of the ancient clades of unicellular relatives of the multicellular animals, ichthyosporea are among the easiest to collect, cultivate, and analyze at the population level. Once identified, species can be correlated with their animal hosts and geographical ranges. However, the spherical stages common to many ichthyosporea provide little basis for morphological species identification.

Molecular phylogeny of unikonts: new insights into the position of apusomonads and ancyromonads and the internal relationships of opisthokonts.

The eukaryotic supergroup Opisthokonta includes animals (Metazoa), fungi, and choanoflagellates, as well as the lesser known unicellular lineages Nucleariidae, Fonticula alba, Ichthyosporea, Filasterea and Corallochytrium limacisporum. Whereas the evolutionary positions of the well-known opisthokonts are mostly resolved, the phylogenetic relationships among the more obscure lineages are not. Within the Unikonta (Opisthokonta and Amoebozoa), it has not been determined whether the Apusozoa (apusomonads and ancyromonads) or the Amoebozoa form the sister group to opisthokonts, nor to which side of the hypothesized unikont/bikont divide the Apusozoa belong.

Facing unknowns: living cultures (Pirum gemmata gen. nov., sp. nov., and Abeoforma whisleri, gen. nov., sp. nov.) from invertebrate digestive tracts represent an undescribed clade within the unicellular Opisthokont lineage ichthyosporea (Mesomycetozoea).

During a culture-based survey of opisthokonts living in marine invertebrate digestive tracts, we isolated two new eukaryotes that differed from described taxa by more than 10% in their small subunit ribosomal DNA sequences. Phylogenetic analysis showed that the two isolates represented a divergent clade of ichthyosporeans known previously only from environmental clone sequences. We used light and electron microscopy to describe the isolates as new genera and species Pirum gemmata and Abeoforma whisleri.

Population-level analyses indirectly reveal cryptic sex and life history traits of Pseudoperkinsus tapetis (Ichthyosporea, Opisthokonta): a unicellular relative of the animals.

We use population genetics to detect the molecular footprint of a sexual cycle, of a haploid vegetative state, and of lack of host specificity in Pseudoperkinsus tapetis, a marine unicellular relative of the animals. Prior to this study, complete life cycles were not known for any of the unicellular lineages sharing common ancestry with multicellular animals and fungi. We established the first collection of conspecific cultures of any member from the unicellular opisthokont lineage ichthyosporea, isolating 126 cultures of P.

Labyrinthulomycetes phylogeny and its implications for the evolutionary loss of chloroplasts and gain of ectoplasmic gliding.

The labyrinthulomycetes, also known as the 'Labyrinthulomycota' are saprotrophic or less frequently parasitic stramenopilan protists, usually in marine ecosystems. Their distinguishing feature is an 'ectoplasmic net,' an external cytoplasmic network secreted by a specialized organelle that attaches the cell to its substrate and secretes digestive enzymes for absorptive nutrition. In this study, one of our aims was to infer the phylogenetic position of the labyrinthulomycetes relative to the non-photosynthetic bicoeceans and oomycetes and the photosynthetic ochrophytes and thereby evaluate patterns of change from photosynthesis to saprotrophism among the stramenopiles.

Multiple isolations of a culturable, motile Ichthyosporean (Mesomycetozoa, Opisthokonta), Creolimax fragrantissima n. gen., n. sp., from marine invertebrate digestive tracts.

A fragrant, spherical, osmotrophic eukaryote was isolated 27 times from the digestive tracts of marine invertebrates collected from the Northeast Pacific. The isolates were cultured from 7 animal collections over a 2-year period, most from the peanut worm, Phascolosoma agassizii. A small subunit ribosomal DNA phylogeny placed the spherical organism within the ichthyosporea, closest to Sphaeroforma arctica and Pseudoperkinsus tapetis.

Phylogeny of marine Gregarines (Apicomplexa)--Pterospora, Lithocystis and Lankesteria--and the origin(s) of coelomic parasitism.

Gregarines constitute a large group of apicomplexans with diverse modes of nutrition and locomotion that are associated with different host compartments (e.g. intestinal lumena and coelomic cavities).