Die ursachen der Temporalvariation von Brachionus calyciflorus Pallas (Rotatoria)

Abstract

1. In the rotifer Brachionus calyciflorus a pair of posterolateral spines (PL) is subjected to extensive temporal variation. The length of these spines may vary from complete absence to more than lorica length. Production of spines is induced by starvation, low temperature, and a substance produced by the predatory rotifer Asplanchna. The aim of this study was, by comparing the effectiveness of these factors, to gain insight into the physiological mechanisms involved, and to assess their relative significance in natural populations. 2. The other spines of the lorica vary in accordance with PL (Fig. 1), however, they never disappear. In the absence of PL, they continue to vary in the same sense (Table 2). 3. In the laboratory starvation and low temperature induce only short PL. To elicit long spines the Asplanchna-substance is always necessary (Fig. 2). The effects of the three factors are additive. High temperature seems to inhibit spine production. The type of the inducing factor has no recognizable influence on the variability of the reaction (Figs. 3 and 4); even under conditions where the reaction is maximal no reduction of the standard deviation is found. 4. There is no clearly recognizable short-term inheritance of spine length: almost the full reaction to each of the inducing factors is realized in the first generation following induction (Fig. 5). 5. Low temperature increases body size. Analysis shows that this temperature effect consists of two components, one acting on egg size, the other on the animals growth after hatching (Figs. 6 and 7). 6. The final spine length is always determined before hatching (Fig. 5). The inducing factors determine the body proportions of the neonates; after hatching the spine length grows allometrically. The average growth rate of the PL relative to that of the body was k=0.54, i.e. the growth rate of the spines is smaller than that of the body (negative allometry). The value of k appears to be a constant, at least it is not influenced by the type of spine induction, the initial spine length, and the conditions after hatching (Table 4 and Fig. 9). 7. Using the allometric relation, an index of spine length (I ) was defined, which is independent of body size. ID permits the quantitative comparison of populations with different age structures, and of age (size) classes within the same sample. Differences between the I -values of the age classes of a sample indicate fluctuations of spine inducing factors (Fig. 10). It is thus possible to estimate the strength of spine inducing factors during previous periods by studying a single plankton sample (Figs. 11 and 12). 8. A reproducible bio-assay was developed to test the spine inducing activity of the medium. A relative unit of Asplanchna-substance (as) was defined. The quantity of substance produced per unit volume and per unit time is proportional to Asplanchna density and is influenced by temperature (within 10 to 25\dg C: Q =4). The amount of substance produced by 1 Asplanchna in 25 sec at 20\dg C in 1 ml medium will induce just...

Rotifers from diapausing, fertilized eggs: Unique features and emergence

“…In the absence of the Asplanchna kairomone, these spines may be completely lacking in some clones or long in other clones. Longer spines can be produced at low temperatures and food concentrations (Halbach 1970;Stemberger 1990). The length of the anterior and posteromedian spines increases with that of the posterolateral spines.…”

Food limitation. spination, and reproduction in Brachionus calyciflorus

“…Although the effect of starvation was recognized in Europe (Buchner et al 1957;Erman 1962;Rauh 1963;Halbach 1970), its ecological significance was not understood. Interest in chemical induction and predation, furthermore, overshadowed the starvation-induced phenomenon.…”

“…The extensive variation in spination and body size of the rotifer BracGonus calyciflorus was noted as early as 1850 (Hudson and Gosse 1886) and has since been the focus of numerous morphological and ecological studies (see Gilbert 1967;Halbach 1970). Explanations of the adaptive significance of the elongation or de novo development of posterolateral spines in the species have included decreased settling velocity (Wesenberg-Lund 1930), enhanced filtration rates (Erman 1962), and predator defense (Beauchamp 1952;Gilbert 1966;Halbath 1970).…”

“…In light of the long history of study on this wellknown polymorphism, I was motivated to redo and expand on key experiments using a single clone of Brachionus and a well-defined Iculture method. I first tested Schneider's ( 1937) finding that low-food conditions induced spine elongation and that low food and Asplanchna-factor together enhanced the degree of spine elongation as reported by Halbach (1970). Analysis of variance of these factors affecting spine length would indicate if they were additive or synergistic and would reveal their relative importance in the polymorphism.…”

“…This argument assumes that the longer spines in Brachionus populations acclimated to low food protect against Asplanchna predation. Because spines become longer when Asplanchna factor is present (Halbach 1970) they must not be long enough to provide complete protection against predation. If long spines are otherwise beneficial during starvation, such as by enhancing feeding rates or reducing swimming costs, then we should expect the defensive (long spined) phenotype irrespective of the presence of Asplanchna factor and food level.…”