Functional Ecology of Two Contrasting Freshwater Ciliated Protists in Relation to Temperature

Abstract

We conducted microcosm experiments with two contrasting freshwater ciliates on functional traits (FTs) related to their growth rate (numerical response, NR) and ingestion rate (functional response, FR) over a range of ecologically relevant temperatures. Histiobalantium bodamicum and Vorticella natans are common planktonic ciliates but their abundance, swimming behavior, and temperature tolerance are different. In contrast to most sessile peritrich species, the motile V. natans is not strictly bacterivorous but also voraciously feeds upon small algae. We observed three main alterations in the shape of NR of both species with temperature, that is, change in the maximum growth rate, in the initial slope and in the threshold food level needed to sustain the population. Similarly, maximum ingestion rate, gross growth efficiency (GGE), and cell size varied with temperature and species. These findings caution against generalizing ciliate performance in relation to the ongoing global warming. Our results suggest that V. natans is the superior competitor to H. bodamicum in terms of temperature tolerance and bottom-up control. However, the abundance of V. natans is usually low compared to H. bodamicum and other common freshwater ciliates, suggesting that V. natans is more strongly top-down controlled via predation than H. bodamicum. The taxonomic position of V. natans has been debated. Therefore, to confirm species and genus affiliation of our study objects, we sequenced their small subunit ribosomal RNA (SSU rDNA) gene. IT has been known for decades that protists represent central nodes in aquatic food webs (Fenchel 1987). As primary producers, predators, food, and parasites, they are structural elements of any aquatic food web and are of tremendous global and local significance for cycling of matter in the ocean and inland water bodies (

Top-down control of planktonic ciliates by microcrustacean predators is stronger in lakes than in the ocean

“…Surprisingly, we found no difference in the microcrustacean feeding rates on the slowly swimming species Vorticella natans and the similar-sized Histiobalantium bodamicum 66 , in contrast to the earlier conjecture that V. natans is more strongly top-down controlled by predation than H. bodamicum 67 . The latter species uses an intermittent swimming behaviour, with immotile floating periods interrupted by sudden, very fast jumps.…”

Dominant marine heterotrophic flagellates are adapted to natural planktonic bacterial abundances

“…Grazing rates directly depend on prey abundance. This dependence, named functional response, has been determined in a variety of marine and freshwater predators (Weisse et al ., 2016 ), including copepods (Henriksen et al ., 2007 ; Isari and Saiz, 2011 ), dinoflagellates (Kim and Jeong, 2004 ; Jeong et al ., 2005 ; Roberts et al ., 2011 ), ciliates (Jonsson, 1986 ; Jürgens and Simek, 2000 ; Gismervik, 2005 ; Lu et al ., 2021 ) and heterotrophic flagellates (Jeong et al ., 2008 ). Functional responses can be fitted to different mathematical models (Holling, 1959 ), being the most popular among ecologists the equivalent to the enzyme kinetic model developed in 1913 by Leonor Michaelis and Maude Menten.…”

Taxonomy and phylogeny of the freshwater tintinnid Tintinnopsis tubuformis Chiang, 1956 (Ciliophora, Oligotrichea) and a proposed synonymization of T. longa nom. corr. Chiang, 1956

“…CILIATES are a crucial component of the planktonic food web, linking the microbial loop with higher trophic levels (Jonsson et al, 2004; Liu et al, 2021; Lu et al, 2021; Romano & Pitta, 2021; Weisse & Montagnes, 2021; Worden et al, 2015; Zingel et al, 2019). The vast majority of described marine planktonic ciliates belong to the tintinnids, whose sampling is facilitated by their rather robust vase‐ or tube‐shaped loricae (shell) produced by the ciliates (Agatha et al, 2013).…”