Effects of diet and laboratory rearing on demography of Dinophilus gyrociliatus (Polychaeta : Dinophilidae)

Life table response experiments were performed to evaluate the demographic consequences of: (1) the dietary regimes and (2) the length of laboratory rearing in strains of Dinophilus gyrociliatus, a small infaunal polychaete. The first experiment was performed using animals recently collected from the natural environment and fed either on spinach or on Tetramin (artificial fish food with high caloric content). Starting from this original group, two distinct laboratory strains were established: the first raised only with spinach, the second only with Tetramin. In the first experiment, the group fed on Tetramin exhibited greater population growth rate (lambda), shorter generation time (T) and reduced expectation of life (e(0)) with respect to the animals fed on spinach. The second experiment took place 2 years later to evaluate the difference in life history traits between these two laboratory strains. In the case of the group fed on Tetramin, population parameters exhibited marked variations; in fact, lambda and the net reproductive rate (R-0) were significantly higher and T and e(0) were shorter than the corresponding parameters observed in the first experiment. Conversely, the demographic variations induced by laboratory rearing on a spinach diet were limited to a reduction in the expectation of life. The decomposition analysis showed that the reduction in generation time and the increase in fecundity occurring during the first 4 weeks of life accounted for nearly all the differences in lambda. During the long breeding period at constant temperature, photoperiod and salinity, a continuous selection of the most precocious and fecund individuals may have taken place as a consequence of the abundance of resources and the lack of predation