Microbial symbioses in marine invertebrates are commonplace. However, characterizations of invertebrate microbiomes are vastly outnumbered by those of vertebrates. Protists and fungi run the gamut of symbiosis, yet eukaryotic microbiome sequencing is rarely undertaken, with much of the focus on bacteria. To explore the importance of microscopic marine invertebrates as potential symbiont reservoirs, we used a phylogenetic-focused approach to analyze the host-associated eukaryotic microbiomes of 220 animal specimens spanning nine different animal phyla.
A morphological and taxonomical account of the taxon Phaenocora is provided. An effort was made to locate and study all available material and, where possible, species are briefly re-described. We also describe two new species: Phaenocora gilberti sp. nov. from Cootes Paradise, Ontario, Canada and Phaenocora aglobulata sp. nov. from Prairie Grove, Alabama, USA. Species recognition is based on a combination of both male and female morphology. A comparison of and discussion on all species is given, resulting in a total of 28 valid species, three species inquirendae, five species dubiae, and one nomen nudum. An identification key is provided.
Improving our understanding of species responses to environmental changes is an important contribution ecologists can make to facilitate effective management decisions. Novel synthetic approaches to assessing biodiversity and ecosystem integrity are needed, ideally including all species living in a community and the dynamics defining their ecological relationships. Here, we present and apply an integrative approach that links high-throughput, multicharacter taxonomy with community ecology. The overall purpose is to enable the coupling of biodiversity assessments with investigations into the nature of ecological interactions in a community-level data set. We collected 1195 gastropods and crabs in British Columbia. First, the General mixed Yule-coalescent (GMYC) and the Poisson Tree Processes (PTP) methods for proposing primary species-hypotheses based on cox1 sequences were evaluated against an integrative taxonomic framework. We then used data on the geographic distribution of delineated species to test species co-occurrence patterns for nonrandomness using community-wide and pairwise approaches. Results showed that PTP generally outperformed GMYC and thus constitutes a more effective option for producing species-hypotheses in community-level data sets. Nonrandom species co-occurrence patterns indicative of ecological relationships or habitat preferences were observed for grazer gastropods, whereas assemblages of carnivorous gastropods and crabs appeared influenced by random processes. Species-pair associations were consistent with current ecological knowledge, thus suggesting that applying community assembly within a large taxonomical framework constitutes a valuable tool for assessing ecological interactions. Combining phylogenetic, morphological and co-occurrence data enabled an integrated view of communities, providing both a conceptual and pragmatic framework for biodiversity assessments and investigations into community dynamics.
Abstract Microturbellarians are abundant and ubiquitous members of marine meiofaunal communities around the world. Because of their small body size, these microscopic animals are rarely considered as hosts for parasitic organisms. Indeed, many protists, both free-living and parasitic ones, equal or surpass meiofaunal animals in size. Despite several anecdotal records of “gregarines”, “sporozoans”, and “apicomplexans” parasitizing microturbellarians in the literature—some of them dating back to the nineteenth century—these single-celled parasites have never been identified and characterized. More recently, the sequencing of eukaryotic microbiomes in microscopic invertebrates have revealed a hidden diversity of protist parasites infecting microturbellarians and other meiofaunal animals. Here we show that apicomplexans isolated from twelve taxonomically diverse rhabdocoel taxa and one species of proseriate collected in four geographically distinct areas around the Pacific Ocean (Okinawa, Hokkaido, and British Columbia) and the Caribbean Sea (Curaçao) all belong to the apicomplexan genus Rhytidocystis . Based on comprehensive molecular phylogenies of Rhabdocoela and Proseriata inferred from both 18S and 28S rDNA sequences, as well as a molecular phylogeny of Marosporida inferred from 18S rDNA sequences, we determine the phylogenetic positions of the microturbellarian hosts and their parasites. Multiple lines of evidence, including morphological and molecular data, show that at least nine new species of Rhytidocystis infect the microturbellarian hosts collected in this study, more than doubling the number of previously recognized species of Rhytidocystis , all of which infect polychaete hosts. A cophylogenetic analysis examining patterns of phylosymbiosis between hosts and parasites suggests a complex picture of overall incongruence between host and parasite phylogenies, and varying degrees of geographic signals and taxon specificity.
In this study we elaborate the phylogeny of Dalytyphloplanida based on complete 18S rDNA (156 sequences) and partial 28S rDNA (125 sequences), using a Maximum Likelihood and a Bayesian Inference approach, in order to investigate the origin of a limnic or limnoterrestrial and of a symbiotic lifestyle in this large group of rhabditophoran flatworms. The results of our phylogenetic analyses and ancestral state reconstructions indicate that dalytyphloplanids have their origin in the marine environment and that there was one highly successful invasion of the freshwater environment, leading to a large radiation of limnic and limnoterrestrial dalytyphloplanids. This monophyletic freshwater clade, Limnotyphloplanida, comprises the taxa Dalyelliidae, Temnocephalida, and most Typhloplanidae. Temnocephalida can be considered ectosymbiotic Dalyelliidae as they are embedded within this group. Secondary returns to brackish water and marine environments occurred relatively frequently in several dalyeliid and typhloplanid taxa. Our phylogenies also show that, apart from the Limnotyphloplanida, there have been only few independent invasions of the limnic environment, and apparently these were not followed by spectacular speciation events. The distinct phylogenetic positions of the symbiotic taxa also suggest multiple origins of commensal and parasitic life strategies within Dalytyphloplanida. The previously established higher-level dalytyphloplanid clades are confirmed in our topologies, but many of the traditional families are not monophyletic. Alternative hypothesis testing constraining the monophyly of these families in the topologies and using the approximately unbiased test, also statistically rejects their monophyly.
To date, sea slugs have been considered the only animals known to sequester functional algal plastids into their own cells, via a process called "kleptoplasty." We report here, however, that endosymbionts in the marine flatworms Baicalellia solaris and Pogaina paranygulgus are isolated plastids stolen from diatoms. Ultrastructural data show that kleptoplasts are located within flatworm cells, while algal nuclei and other organelles are absent. Transcriptomic analysis and rbcL amplicons confirm the absence of algal nuclear mRNA and reveal that the plastids originate from different species of diatoms. Laboratory experiments demonstrated photosynthetic activity and short-term retention of kleptoplasts in starved worms. This lineage of flatworms represents the first known case of functional kleptoplasty involving diatoms and only the second known case of kleptoplasty across the entire tree of animals.
Additional file 1: Supplementary Table 1. Number of Apicomplexa, Ciliophora and Fungi ASVs in each host phylum. n.pos = number of specimens positive for microeukaryote in question, spec.total = total number of specimens, prop.pos = proportion of positive specimens (%), n.uniq.ASVs = number of unique ASVs per host phylum.
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