Abstract
Summary Life-cycle theory predicts that a trade-off exists between somatic maintenance and reproduction. Short-lived semelparous organisms, with a high investment in reproduction, should have lower levels of somatic cell turnover leading to accelerated senescence and reduced post-reproductive survival, than long-lived iteroparous organisms. This model has been tested by intraspecific comparison of mitotic rates and rates of regeneration, taken as indexes of somatic cell population dynamics, between two different populations of a reportedly semelparous species of freshwater triclad, Dendrocoelum lacteum, and a population of the iteroparous species Dugesia(S)mediterranea. Mitotic activity and rate of regeneration were found to increase from northern (N) to southern (S) populations of D. lacteum and from the latter to D.(S)mediterranea; this trend is opposite to that found for reproductive investment in the same populations. Both features agree with reports of true semelparity for N populations and presumed iteroparity for S populations. The implications of these results as regards life-cycle theory and the cellular basis of cell renewal and regeneration in freshwater triclads are discussed.
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