6 results found
Wilson CG, Nowell R, Barraclough T, 2018, Cross-contamination explains "inter- and intraspecific horizontal genetic transfers" between asexual bdelloid rotifers, Current Biology, Vol: 28, Pages: 2436-2444.e14, ISSN: 1879-0445
A few metazoan lineages are thought to have persisted for millions of years without sexual reproduction. If so, they would offer important clues to the evolutionary paradox of sex itself [1, 2]. Most "ancient asexuals" are subject to ongoing doubt because extant populations continue to invest 17 in males [3–9]. However, males are famously unknown in bdelloid rotifers, a class of microscopic invertebrates comprising hundreds of species [10–12]. Bdelloid genomes have acquired an unusually high proportion of genes from non-metazoans via horizontal transfer [13–17]. This well-substantiated finding has invited speculation  that homologous horizontal transfer between bdelloid individuals also may occur, perhaps even "replacing" sex . In 2016, Current Biology published an Article claiming to supply evidence for this idea. Debortoli et al.  sampled rotifers from natural populations and sequenced one mitochondrial and four nuclear loci. Species assignments were incongruent among loci for several samples, which was interpreted as evidence of "interspecific horizontal genetic transfers". Here, we use sequencing chromatograms supplied by the authors to demonstrate that samples treated as individuals actually contained two or more highly divergent mitoc hondrial and ribosomal sequences, revealing cross-contamination with DNA from multiple animals of different species. Other chromatograms indicate contamination with DNA from conspecific animals, explaining genetic and genomic evidence for "intraspecific horizontal exchanges" reported in the same study. Given the clear evidence of contamination, the data and findings of Debortoli et al.  provide no reliable support for their conclusions that DNA is transferred horizontally between or within bdelloid species.
Barraclough TG, Nowell R, Wilson C, et al., 2018, Comparative genomics of bdelloid rotifers: insights from desiccating and nondesiccating species, PLoS Biology, Vol: 16, ISSN: 1544-9173
Bdelloid rotifers are a Class of microscopic invertebrates that have existed for millions of years apparently without sex or meiosis. They inhabit a variety of temporary and permanent freshwater habitats globally, and many species are remarkably tolerant of desiccation. Bdelloids offer an opportunity to better understand the evolution of sex and recombination, but previous work has emphasized desiccation as the cause of several unusual genomic features in this group. Here, we present high-quality whole genome sequences of three bdelloid species: Rotaria macrura and Rotaria magnacalcarata, which are both desiccation intolerant, and Adineta ricciae, which is desiccationtolerant. In combination with the published assembly of Adineta vaga, which is also desiccation tolerant, we apply a comparative genomics approach to evaluate the potential effects of desiccation tolerance and asexuality on genome evolution in bdelloids. We find that ancestral tetraploidy is conserved among all four bdelloid species, but homologous divergence in obligately aquatic Rotaria genomes is unexpectedly low. This finding is contrary to current models regarding the role of desiccation in shaping bdelloid genomes. In addition, we find that homologous regions in A. ricciaeare largely collinear and do not form palindromic repeats as observed in the published A. vaga assembly. Consequently, several features interpreted as genomic evidence for long-term ameiotic evolution are not general to all bdelloid species, even within the same genus. Finally, we substantiate previous 50 findings of high levels of horizontally transferred non-metazoan genes in both desiccating and non-desiccating bdelloid species, and show that this unusual feature is not shared by other animal phyla, even those with desiccation-tolerant representatives. These comparisons call
Wilson CG, Sherman PW, 2013, Spatial and temporal escape from fungal parasitism in natural communities of anciently asexual bdelloid rotifers, PROCEEDINGS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, Vol: 280, ISSN: 0962-8452
Wilson CG, 2011, Desiccation-tolerance in bdelloid rotifers facilitates spatiotemporal escape from multiple species of parasitic fungi, BIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Vol: 104, Pages: 564-574, ISSN: 0024-4066
Wilson CG, Sherman PW, 2010, Anciently Asexual Bdelloid Rotifers Escape Lethal Fungal Parasites by Drying Up and Blowing Away, SCIENCE, Vol: 327, Pages: 574-576, ISSN: 0036-8075
Wilson CG, 2008, Male genital mutilation: an adaptation to sexual conflict, Evolution and Human Behavior, Vol: 29, Pages: 149-164, ISSN: 1090-5138
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