The Relationship Between Ration, Reproductive Effort and Age-Specific Mortality in the Evolution of Life-History Strategies--Some Observations on Freshwater Triclads

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Abstract
The annual triclad Dendrocoelum lacteum preserved egg capsule output to a greater extent under conditions of nutritive stress than the perennial species, Dugesia lugubris and Polycelis tenuis. Under normal nutritive conditions reproductive effort was higher in D. lacteum than in P. tenuis. As food supply was reduced reproductive effort rose 10-fold in D. lacteum but only 3-fold in P. tenuis. There was a direct and significant relationship between adult mortality and the effort put into reproduction in D. lacteum. The hatchlings of D. lacteum were better able to cope with feeding disturbances than those of P. tenuis. Differences in the susceptibility of hatchlings to nutritive disturbance may have been instrumental in the evolution of differences in reproductive strategy between species.