Brachionus is a genus of planktonic rotifers occurring in freshwater, alkaline and brackish water.
Species The following species are recognised in the genus Brachionus:
Brachionus adisi Brachionus africanus Brachionus ahlstromi Brachionus amazonicus Brachionus amsterdamensis Brachionus angularis Brachionus araceliae Brachionus asplanchnoidis Brachionus austrogenitus Brachionus baylyi Brachionus bennini Brachionus bidentatus Brachionus budapestinensis Brachionus calyciflorus Brachionus caudatus Brachionus charini Brachionus chelonis Brachionus dichotomus Brachionus dimidiatus Brachionus diversicornis Brachionus dolabratus Brachionus donneri Brachionus dorcas Brachionus durgae Brachionus elevatus Brachionus falcatus Brachionus fernandoi Brachionus forficula Brachionus gessneri Brachionus gillardi Brachionus havanaensis Brachionus huangi Brachionus ibericus Brachionus incertus Brachionus josefinae Brachionus keikoa Brachionus koreanus Brachionus kostei Brachionus kultrum Brachionus leydigii Brachionus lyratus Brachionus macrocanthus Brachionus manjavacas Brachionus mirabilis Brachionus mirus Brachionus murphyi Brachionus nilsoni Brachionus novaezealandiae Brachionus paranguensis Brachionus pinneenaus Brachionus plicatilis Brachionus postcurvatus Brachionus pseudodolabratus Brachionus pseudonilsoni Brachionus pterodinoides Brachionus quadridentatus Brachionus rotundiformis Brachionus rubens Brachionus satanicus Brachionus schwoerbeli Brachionus sericus Brachionus sessilis Brachionus spatiosus Brachionus srisumonae Brachionus urceolaris Brachionus variabilis Brachionus zahniseri
Use Rotifers such as Brachionus calyciflorus are favored test animals in aquatic toxicology because of their sensitivity to most toxicants. They also are used as model organisms in various other biological fields e.g. due to their interesting reproductive mode in evolutionary ecology. Brachionus spp. are easily reared in large numbers and because of this are used to substitute for wild zooplankton for feeding hatchery reared larval fish. However, the composition of rotifers generally does not satisfy the nutritional requirements of fish larvae, and large amounts of research have been invested in improving the lipid, vitamin and mineral composition of rotifers to better meet the requirements of fish larvae
Reproduction Brachionus species can normally reproduce sexually and asexually (cyclical parthenogenesis). Sexual reproduction (termed Mixis) is usually induced when population density increases. Mixis in Brachionus plicatilis has been shown to be induced by a density-dependent chemical cue.Induction of sexual reproduction in Brachionus plicatilis (Monogononta, Rotifera) by a density-dependent chemical cue CP Stelzer, TW Snell - Limnology and Oceanography, 2003
Transitions to obligate parthenogenesis have been described in Brachionus calyciflorus. In this species, obligate parthenogenesis can be inherited by a recessive allele, which leads to loss of sexual reproduction in homozygous offspring.C.-P. Stelzer, J. Schmidt, A. Wiedlroither, and S. Riss (2010). Loss of Sexual Reproduction and Dwarfing in a Small Metazoan. PLoS ONE 5(9): e12854. Scheuerl, T., Riss, S., Stelzer, C.P. (2011). Phenotypic effects of an allele causing obligate parthenogenesis in a rotifer. Journal of Heredity 102(4): 409-415. http://jhered.oxfordjournals.org/cgi/reprint/esr036?ijkey=94jzFn7JvmYfQyM&keytype=ref In Brachionus manjavacas rotifers, offspring's survival and its cell's ability to growth and division decrease with advancing age of mother.
Genome size Haploid '1C' genome sizes in Brachionus species range at least from 0.056 to 0.416 pg.Stelzer, C.P., Riss, S., Stadler, P. (2011) Genome size evolution at the speciation level: The cryptic species complex Brachionus plicatilis (Rotifera) BMC Evolutionary Biology 11: 90.
Genome sequencing The complete mitochondrial genome of B. plicatilis sensu stricto NH1L has been sequenced.Koushirou Suga, David B. Mark Welch, Yukari Tanaka, Yoshitaka Sakakura, and Atsushi Hagiwara (2008). Two Circular Chromosomes of Unequal Copy Number Make Up the Mitochondrial Genome of the Rotifer Brachionus plicatilis Mol Biol Evol (2008) 25(6): 1129-1137
Cryptic species Brachionus plicatilis has been demonstrated to be a large cryptic species complex consisting of several different species. It has a worldwide diversity of at least 14 - 22 cryptic taxa.Extreme levels of hidden diversity in microscopic animals (Rotifera) revealed by DNA taxonomy D Fontaneto, M Kaya, EA Herniou… - Molecular Phylogenetics …, 2009 - ElsevierDiversity of the rotifer Brachionus plicatilis species complex (Rotifera: Monogononta) in Iran through integrative taxonomy Reza Malekzadeh-Viayeh1,*, Razieh Pak-Tarmani1, Nasim Rostamkhani2 and Diego Fontaneto3 Article first published online: 7 JAN 2014 DOI: 10.1111/zoj.12106
Brachionus calyciflorus also seems to be a cryptic species complex.Brachionus calyciflorus is a species complex: mating behavior and genetic differentiation among four geographically isolated strains JJ Gilbert, EJ Walsh - Rotifera X, 2005 - Springer
References
Huang, L. "Effectof Aldrin on Life History Characteristics of Rotifer Brachionus calyciflorus Pallas." Bull Environ Contam Toxicol no5 N 2007