Journal Article

Intraspecific trait variation alters the outcome of competition in freshwater ciliates

Brinkhoff, Thorsten, Gaedke, Ursula, Yong, Joanne, Moorthi, Stefanie, Flöder, Sabine, Poprick, Tobias, Klauschies, Toni

2021

Overview

Trait variation among heterospecific and conspecific organisms may substantially affect community and food web dynamics. While the relevance of competition and feeding traits have been widely studied for different consumer species, studies on intraspecific differences are more scarce, partly owing to difficulties in distinguishing different clones of the same species. Here, we investigate how intraspecific trait variation affects the competition between the freshwater ciliates Euplotes octocarinatus and Coleps hirtus in a nitrogen‐limited chemostat system. The ciliates competed for the microalgae Cryptomonas sp. (Cry) and Navicula pelliculosa (Nav), and the bacteria present in the cultures over a period of 33 days. We used monoclonal Euplotes and three different Coleps clones (Col 1, Col 2, and Col 3) in the experiment that could be distinguished by a newly developed rDNA‐based molecular assay based on the internal transcribed spacer (ITS) regions. While Euplotes feeds on Cry and on bacteria, the Coleps clones cannot survive on bacteria alone but feed on both Cry and Nav with clone‐specific rates. Experimental treatments comprised two‐species mixtures of Euplotes and one or all of the three different Coleps clones, respectively. We found intraspecific variation in the traits “selectivity” and “maximum ingestion rate” for the different algae to significantly affect the competitive outcome between the two ciliate species. As Nav quickly escaped top‐down control and likely reached a state of low food quality, ciliate competition was strongly determined by the preference of different Coleps clones for Cry as opposed to feeding on Nav. In addition, the ability of Euplotes to use bacteria as an alternative food source strengthened its persistence once Cry was depleted. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition. Intraspecific variation in the traits “selectivity” and “maximum ingestion rate” for their prey significantly affected the competition between two freshwater ciliate species. Exclusion of either one of the ciliates or long‐term persistence depended on which of the competitors benefited more from feeding on a less abundant algal resource of high food quality, on severe nutrient limitation that affected the food quality of the dominant algal resource, and on the ability of one competitor to use bacteria as an alternative food source. Hence, trait variation at both trophic levels codetermined the population dynamics and the outcome of species competition.

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc,Wiley
• Subject: Algae / Bacteria / Biomass / Bioreactors / Carbon / ciliate predators / Ciliates / Cloning / Coleps / Competition / Euplotes / Experiments / Food / Food chains / Food quality / Food sources / Food webs / Freshwater organisms / Ingestion / intraspecific trait variation / microalgal resource / Organisms / Original Research / Population dynamics / predator trait variation / predator–prey systems / resource competition / Selectivity / Species / Trophic levels / Variation