The Clonal Ecology of Heterocypris incongruens (Ostracoda)

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Abstract
A seasonal cycle in the frequency of electrophoretically distinguishable clones has been followed from late July 1985 to early August 1987 in an obligate parthenogenetic population of Heterocypris incongruens (Ramdohr) in a rice field located in the Po plain (Italy). Different clones predominate at different seasons. Summer and winter allozyme clones show size differences: otherwise the clones show no distinctive morphological features. The dimensional nature of the observed differences has been confirmed by multivariate analysis of 19 quantitative morphological traits. The electrophoretic clones reared in the laboratory at different temperatures (4.degree., 16.degree., 24.degree., 28.degree., 32.degree. C) have survival curves and relative abundances that vary with temperature. In the laboratory, the clone dominant in the field in winter fares better at low temperatures while the clone dominant in the summer does so at high temperatures. Temperature is a likely selective factor responsible for the observed seasonal cycles in the field.