Changes in the population structure of the rotifer Brachionus plicatilis under controlled conditions

V. Kostopoulou, G. Katis, H. Miliou, G. Verriopoulos-2003

Abstract:

Two experiments, using 4-day rotifer batch cultures, were conducted in order to investigate possible changes in the population structure of Brachionus plicatilis in relation to feeding regimes and rotifer densities. All rotifer populations were fed on Tetraselmis suecica. The first experiment comprised two treatments (3 replicates): rotifer also supplied with yeast (A populations) and rotifers also supplied with Culture Selco (B populations). The second experiment comprised three treatments (3 replicates): rotifers also supplied with yeast (C populations) and rotifers also supplied with Culture Selco (D and E populations). Rotifer densities were significantly higher in A, C en E than in the B and D populations. The offered daily amount of phytoplankton per rotifer was about 20 times higher in the second experiment compared to the first (70 cells/rotifer/day). Samples were collected daily, morning and afternoon. The population structure was described as follows: eggs, immature females, mature females without eggs, females with sac, females with one, two, three or more eggs, post-reproductive females and degenerate rotifers. Multivariate analysis discriminated A from B populations in the first experiment and C from D and E populations in the second. A and C populations were characterizes by mature females without eggs, while B, D and E populations were characterized by females with 2 and 3 eggs and degenerate rotifers. A and C  populations showed significant diurnal variation; females with eggs dominated in the morning, and immature rotifers and females with sac in the afternoon. B, D and E populations showed significant daily variations, the most important being an increased number of females with eggs on the second and third day. Specific growth rate did not significantly vary amongst treatments. The results indicated number of females with eggs on the second and third day. Specific growth rate did not significantly vary amongst treatments. The results indicated that the observed changes in population structure could be attributed to the quality of food, but not to the quantity of phytoplankton or the density of rotifers.

(Depart of Zoology-Marine Biology, Faculty of Biology, National and Kapodistrian University of Athens, Panepistimiopolis, Athens 157 84, Greece, e-mail: vkostop@biol.uoa.gr)

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