A field and laboratory study on factors affecting polymorphism in the rotifer Keratella tropica

CRISTINA MARINONE, MARÍA; HORACIO ZAGARESE

OECOLOGIA

Año: 1991 vol. 86 p. 372 - 377

0029-8549

Summary. We present data on polymorphism of therotifer Keratella tropica from an outdoor, mesoscale experimentand a series of laboratory induction assays. Inthe outdoor experiment the biomass of planktonic crustaceanswas noticeably depressed by larval fish predation,and associated with this depression K. tropica underwenta striking reduction of caudal spines. Subsequentlaboratory studies showed that the positive associationbetween crustacean biomass and caudal spinelength was a cause and effect relationship. This is the firstrecord of rotifer morphological change as an indirecteffect of fish predation. In laboratory experiments filtratesof monospecific cultures of a cyclopoid copepod,a calanoid copepod and 5 cladocerans induced a remarkablespine development. Morphological inductionshowed a direct relationship with the concentration ofcrustaceans, both under field and laboratory conditions.Long spines were found to be strong deterrents againstsmall predators (Acanthocyclops robustus copepodites),but were useless against large ones (females of the samespecies). The morphotypes of K. tropica obtained byexperimental induction from a single clone encompassmuch of the worldwide variation of the species.