engleski

Hydra vs. turbellarians: who is the strongest constituent in a given micro-(eco)system? – preliminary observations

The goal of this research was to study interactions among carnivorous invertebrates: green hydra (Hydra viridissima Pallas, 1766), and turbellarians Dugesia gonocephala (Duges, 1830) and Polycelis felina (Dalyell, 1814). In ex situ microcosms experiment animals were exposed through the day-night rythm (8 h light/16 h dark) and different light and temperature (25 °C/13.5 °C) conditions, both separately with starved and fed animals. The results were recorded immediately after the experiment setup and every 1, 8 and 24 hs after the beginning of the experiment, including the controls. Experiment was set up with 1 and 5 animals of each species, 5 replicas for each setup. In the view of interference competition, behaviour indicated habitat separation: fed D. gonocephala was resting on the side and hydra on the bottom of microcosm, with partial migrations in water column. Starved D. gonocephala were agile and hydra was on the bottom of microcosm, with no migrations present. In microcosm with fed P. felina, hydra was budding and P. felina were mainly resting. Starved specimens of P. felina were active and hydras were relaxed. Interspecies predation occurred between D. gonocephala as a predator and P. felina as a prey, mainly observed with starved animals. P. felina used aggregation as the mechanism of protection. Results of this study suggested hydra as better-equipped predator, probably due to cnidocytes, than turbellarians. Two or more predatory groups can coexist, however closely related interspecies predation could appear.

Hydra ; planarians ; microcosm

ISSN 2459-8402