Effects of DDT on longevity and reproductive rate in Lepidodermellasquammata (Gastrotricha, Chaetonotida)

Demographic life history data are used as a means of assessing effects of increasing concs of DDT on the longevity and reproductive rate of L.squammata, a common aquatic micrometazoan. These obligate parthenogens were cultured individually in slide depressions, each juvenile being transferred to its own depression upon hatching. Life history data were collected at 0.5-day intervals for 57-69 individuals each under conditions of control, 0.05, 0.5, 5 and 50 ppm DDT in final solution. Data were assembled into life tables and values, of e Sub(x), R Sub(o) and r Sub(m) were calculated. Values of all 3 parameters decrease with increasing concs of DDT. Even at 0.05 ppm DDT, a conc too low to allow detection using data from lethal conc tests, the intrinsic rate of natural increase shows a 10% selective disadvantage associated with the presence of DDT. The method has great potential as an analytic tool, compared with the results of tolerance tests, because of its sensitivity to minute amounts of pollutants. Results are related to the Hutchinsonian concept of niche. It is shown, further, that while the same general relationships would be expected to occur in the field, mortality resulting from a pollutant would largely be masked under field conditions by mortality from other sources.