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The Effect of Temperature on the Life-Cycle of Four Species of Lake-Dwelling Triclads

T. B. Reynoldson, J. O. Young and Margaret C. Taylor
Journal of Animal Ecology
Vol. 34, No. 1 (Feb., 1965), pp. 23-43
DOI: 10.2307/2367
Stable URL: http://www.jstor.org/stable/2367
Page Count: 21
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The Effect of Temperature on the Life-Cycle of Four Species of Lake-Dwelling Triclads
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Abstract

1. The effect of constant temperatures on cocoon production, incubation period, development of young to maturation and the complete cycle of Polycelis nigra (Müll.), P. tenuis (Ijima), Dugesia lugubris (O. Schmidt) and Dendrocoelum lacteum (Müll.) has been studied over a range of 1.5-25 degrees C. 2. D. lacteum is the species most tolerant of cold and least tolerant of heat, and can complete more generations per year than the others below 10 degrees C. Dugesia lugubris is least tolerant of cold and most tolerant of heat, and can complete more generations than the others above 10 degrees C. The Polycelis species are intermediate with P. nigra slightly more tolerant of cold than P. tenuis. 3. Failure to breed at low temperatures was in part due to retardation in testis development. At high temperatures both testes and ovaries were adversely affected. But failure to copulate, to produce cocoons, to develop and mature at low and high temperatures also determined the thermal ecology of the species. 4. The temperature thresholds for breeding in these triclad species as determined by laboratory experiments agreed with field data on this parameter and was further confirmed by outdoor experiments with P. tenuis and Dugesia lugubris. 5. Comparison of the thermal ecology of these organisms with the climate of their areas of distribution suggested that temperature may be a contributory factor in determining distribution except for Dendrocoelum lacteum in Britain.

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