Main Content

The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Ref ID : 672

Maria Cristina Marinone and Horacio E. Zagarese; A field and laboratory study on factors affecting polymorphism in the rotifer Keratella tropica. Oecologia (Berlin) 86:372-377, 1991

Reprint

In File

Notes

We present data on polymorphism of the rotifer Keratella tropica from an outdoor, mesoscale experiment and a series of laboratory induction assays. In the outdoor experiment the biomass of planktonic crustaceans was noticeably depressed by larval fish predation, and associated with this depression K. tropica underwent a striking reduction of caudal spines. Subsequent laboratory studies showed that the positive association between crustacean biomass and caudal spine length was a cause and effect relationship. This is the first record of rotifer morphological change as an indirect effect of fish predation. In laboratory experiments filtrates of monospecific cultures of a cyclopoid copepod, a calanoid copepod and 5 cladocerans induced a remarkable spine development. Morphological induction showed a direct relationship with the concentrations of crustaceans, both under field and laboratory conditions. Long spines were found to be strong deterrents against small predators (Acanthocyclops robustus copepodites), but were useless against large ones (females of the same species). The morphotypes of K. tropica obtained by experimental induction from a single clone encompass much of the worldwide variation of the species.