by Piter Kehoma Boll
Charles Darwin had already noticed that small animals, such as those found in zooplankton, are widely distributed around the world, even those that are found in small ponds of freshwater. This seemed to go against the speciation theories, but it was thought to be the result of passive transport by other animals, such as migratory birds. One of such species is the tiny rotifer Brachionus plicatilis, or the pliable brachionus, as I decided to call it, a 0.1 to 0.2 mm long species found worlwide in saline lakes.
The pliable brachionus is a euryhaline species, meaning it can tolerate a wide range of salinity. Recent molecular studies have shown that it is actually a complex of at least 22 different species, but as this was not yet taxonomically defined, I will continue to use the terms Brachionus plicatilis and plicate brachionus in the broad sense.
In the last half century, the pliable brachionus became a commercially important species, being raised as a food source for fish larvae. It may be fed with a variety of microorganisms, such as bacteria, algae and yeasts. In the natural environment, it is considered a generalist filter-feeding species.
As many rotifers, the pliable brachionus usually reproduces by parthenogenesis, where the so-called amictic females produce diploid eggs that originate other amictic females. Under certain conditions, however, they may produce eggs that originate mictic females, which only lay haploid eggs. Unfertilized haploid eggs originate males, while those that are fertilized originate new females. A bit complex, right?
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Gómez, A., Serra, M., Carvalho, G., & Lunt, D. (2002). Speciation in ancient cryptic species complexes: evidence from the molecular phylogeny of Brachionus plicatilis(Rotifera) Evolution, 56 (7) DOI: 10.1554/0014-3820(2002)056[1431:SIACSC]2.0.CO;2
Øie, G., Makridis, P., Reitan, K., & Olsen, Y. (1997). Protein and carbon utilization of rotifers (Brachionus plicatilis) in first feeding of turbot larvae (Scophthalmus maximus L.) Aquaculture, 153 (1-2), 103-122 DOI: 10.1016/S0044-8486(96)01514-1
Suatoni, E., Vicario, S., Rice, S., Snell, T., & Caccone, A. (2006). An analysis of species boundaries and biogeographic patterns in a cryptic species complex: The rotifer—Brachionus plicatilis Molecular Phylogenetics and Evolution, 41 (1), 86-98 DOI: 10.1016/j.ympev.2006.04.025
Walker, K. (1981). 13. A synopsis of ecological information on the saline lake rotifer Brachionus plicatilis Müller 1786 Hydrobiologia, 81-82 (1), 159-167 DOI: 10.1007/BF00048713
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