Ref ID : 3232
Birger Pejler; On the variation of the Rotifer Keratella cochlearis (Gosse). Zool.Bidr.,Upps. 35:1-17, 1962
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1. The local variation of K. cochlearis is described and analysed on the basis of a material from lakes in Central Sweden. There are strong allometric correlations between the three characters measured, viz. body length, length of posterior spine and body breadth. 2. In lakes with low transparency values the K. cochlearis forms are invariably smaller and more short-spined (often lacking the posterior spine) than in other waters. Transparency is here taken as a crude indicator of biological production, and spine-length and body size thus appear to be correlated with production. 3. As seasonal variation is considered to be induced mainly by temperature changes, and the present local variation largely by primary production, it is natural to look for a common denominator for these two factors. The growth-rate seems to be such a denominator, as other authors have found that it accelerates with rising temperature as well as with an increasing amount of food. 4. The differences in viscosity between the waters of different types of lakes are proved to be extremely small. Thus Ostwald's viscosity theory cannot explain the local variation in the present material. Nor can it explain the seasonal variation, as this has a course reversed to that expected if the viscosity theory held true. 5. The variation in spine-length is considered to have the advantage mainly of compensating for the strongly altered weight resulting from a relatively slight change in body length. The body size is thus regarded as the primary phenomenon, the spine-length as secondary.