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Enzyme Variability in Natural Populations of Daphnia magna. I. Population Structure in East Anglia

Paul D. N. Herbert
Evolution
Vol. 28, No. 4 (Dec., 1974), pp. 546-556
DOI: 10.2307/2407280
Stable URL: http://www.jstor.org/stable/2407280
Page Count: 11
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Enzyme Variability in Natural Populations of Daphnia magna. I. Population Structure in East Anglia
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Abstract

The low rates of evolutionary divergence among passively dispersing freshwater organisms have generally been related to high vagility. In contrast the present study shows that gene flow among populations of Daphnia magna in East Anglia is extremely limited. Highly significant differences in allelic frequencies are present between populations isolated by only a few metres, while allelic substitution is prevalent among populations separated by more than 100 metres. Genetic differentiation over large areas is not, however, significantly greater than that observed locally. The distribution pattern of allelic variation suggests that founder effects have played the major role in determining the allelic array of individual populations, although selective forces are implicated in the maintenance of variability. Fragmentation of a species gene pool into many isolated demes reduces the directional response to selection gradients and probably is a major factor in explaining the geographical uniformity of passively dispersing pond organisms.

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