Genome size and lifestyle in gnesiotrochan rotifers
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Gnesiotrochan rotifers display a variety of life styles ranging from taxa with free-swimming larval and sessile adult stages to those with motile adult stages and colonial habits. Several explanations for the C-value enigma posit that genome size is correlated with lifestyle. To investigate this, 13 gnesiotrochan species representing nine genera were measured by flow cytometry. Genome sizes (1C) within Gnesiotrocha ranged from 0.05 pg (Hexarthra mira and Hexarthra fennica) to 0.25 pg (Sinantherina ariprepes). Genome sizes varied within genera and species; e.g., the H. fennica (El Huérfano, Mexico) genome was estimated to be 15% larger than that of H. mira and H. fennica (Keystone Wetland, TX, USA). Gnesiotrochan genome sizes are similar to those reported within Ploima, which range from 0.06 pg (Brachionus rotundiformis, B. dimidiatus) to 0.46 pg (B. asplanchnoidis). Within Gnesiotrocha, genome size was found to be significantly smaller in sessile versus motile species as well as in solitary versus colonial species. To account for phylogenetic background, linear mixed models with hierarchical taxonomic ranks showed that there is a taxonomic component underlying genome size. This study provides the first estimates of genome size within the superorder, providing a baseline for genomic and evolutionary studies within the group.
KeywordsC-value Coloniality Flow cytometry Free-swimming Sessile
Funding was provided by NSF DEB-1257068 (EJW), National Institute of Health (NIH-NIMHD-RCMI 5G12MD007592), and UTEP’s Dodson research Grant (PDB). Samples were collected under permits TPWD 2016-03, CPDCNBSP-2016-32, and EMNRDSPD 2017. Support from CONABIO “Inventario Multitaxonómico del ANP Médanos de Samalayuca” PJ018, facilitated collections from El Huérfano, Chihuahua, MX (EJW, JRA; SEMARNAT SGPA/DGVS/04784/17). Travis LaDuc facilitated collection at Miller Ranch. Kevin Bixby provided access to La Mancha Wetland. Australian sediment samples were kindly provided by John Gilbert and Russell Shiel. Nic Lannutti, Rick Hochberg, Kevin Floyd, Sergio Samaniego, Enrique Garcia, Judith Ríos-Arana (JRA), and Robert L. Wallace provided plankton and/or vegetation samples. We thank Armando Varela for his help with flow cytometry (BBRC CSI Core Facility, funded by NIH-NIMHD-RCMI 5G12MD007592), Kyung-An Han for providing Drosophila and her students for help with rearing them, and Claus-Peter Stelzer for his advice on flow cytometry methods for rotifers. Robert L. Wallace, the guest editors of the rotifer symposium volume, and two anonymous reviewers made helpful suggestions that greatly improved this manuscript.
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