r-and K-selection in soil ciliates: a field and experimental approach

Area of Science:

• Ecology
• Evolutionary Biology
• Microbiology

Background:

• The r/K selection theory, a model of reproductive strategies, has been suggested for terrestrial ciliates.
• Understanding ciliate distribution in diverse habitats is crucial for ecological studies.

Purpose of the Study:

• To investigate the species composition and abundance of Colpodea and Polyhymenophora in alpine and lowland sites.
• To compare the ecological and reproductive strategies of selected Colpodea and Polyhymenophora species under laboratory conditions.
• To determine if Colpodea exhibit r-selected traits compared to Polyhymenophora.

Main Methods:

• Field census of dominant ciliate groups (Colpodea, Polyhymenophora) in predictable (lowland) and unpredictable (alpine) sites.
• Laboratory experiments on representative species (Colpoda aspera, Grossglockneria acuta, Blepharisma undulans, Gonostomum affine) assessing fertility, environmental tolerance, and population growth.
• Analysis of the Colpodea/Polyhymenophora (C/P) index, opportunism, competitive ability, and body size.

Main Results:

• The C/P index was higher in unpredictable alpine sites compared to predictable lowland sites.
• Colpodea species (C. aspera, G. acuta) showed greater tolerance to temperature changes, faster population growth, and higher densities than Polyhymenophora species (B. undulans, G. affine).
• Colpodea's reproductive strategy, including quadripartition in cysts, contributes to rapid population increases.

Conclusions:

• Colpodea demonstrate characteristics of r-selected species, contrasting with the K-selected traits of Polyhymenophora.
• The r-selected nature of Colpodea provides a potential explanation for their widespread distribution and high abundance in challenging terrestrial environments.