Adaptive motility and feeding strategies of deep-branching predatory protists
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Abstract
Heterotrophic flagellates play a major role in nutrient recycling and shaping aquatic microbial communities. Many motile species have evolved diverse predatory strategies to exploit microbial prey, from bacteria to small eukaryotes. Excavates, deep-branching eukaryotic lineages with distinctive biflagellate morphology and conserved cytoskeletal features, exhibit varied feeding behaviours, including grazing, raptorial feeding, and filter-feeding. However, the temporal dynamics of their motility, feeding, and spatial distribution in relation to bacterial population density remain under-explored. Here, we quantify the behavioural ecology of excavates using high-resolution, single-cell tracking and quantitative analysis. Focussing on two Discoba species – the marine Jakoba libera and freshwater Reclinomonas americana – we identify different behavioural patterns: J. libera swims, forages and feeds, while R. americana swims and feeds. Prey availability differentially affects motility: J. libera increases the number of swimming cells when food is scarce, while R. americana shows the opposite trend. Spatial statistics reveal fundamental differences in their feeding and redistribution strategies. J. libera acts as an active forager, whereas R. americana behaves as a strict filter feeder. A third species, the anaerobic Kipferlia bialata (from a different clade), adopts a foraging strategy similar to J. libera . Together, these results elucidate the adaptive relationship between prey availability, feeding modes, and motility in bacteriovorous excavate flagellates, offering new insights into the ecological and evolutionary dynamics of microbial predators.
Microbial hunters and predators that feed on other small organisms play an important role in aquatic food webs. Many species are motile, with seemingly adaptive behaviours that are difficult to quantify. Here, we focus on different species of early-diverging biflagellates that share a common morphology consisting of two flagella and a feeding groove, which it uses to feed on surface-associated bacterial prey. We demonstrate how the predator’s behavioural profiles shift as prey abundance changes over many days of a culture cycle, accompanied by evolving patterns of spatial distribution. Species-specific differences provide insights into the mechanisms of environmental adaptation in early eukaryotes.
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The strong dependence of the motility on prey availability, rather than prey density, hints at possible competition between predators. Cells may be vying to occupy the same bacterial hotspots (see Movie S6 and Fig. S8).
This is a really cool interaction. The cell that gets pushed off does not just wander away. It takes a long loop and comes back to the same patch from the other side, and the two swap again. I would love to know how often this happens, or whether this movie is the one time you caught it.
The patch is interesting too. The cultures carry their own bacteria, and Figure S2 looks like a mix of sizes and shapes rather than one cell type. Is that hotspot a thicker patch of the same bacteria, or could it be a different bug?
While a cell is feeding, the anterior flagellum is attached and the posterior one beats in the groove, …
The strong dependence of the motility on prey availability, rather than prey density, hints at possible competition between predators. Cells may be vying to occupy the same bacterial hotspots (see Movie S6 and Fig. S8).
This is a really cool interaction. The cell that gets pushed off does not just wander away. It takes a long loop and comes back to the same patch from the other side, and the two swap again. I would love to know how often this happens, or whether this movie is the one time you caught it.
The patch is interesting too. The cultures carry their own bacteria, and Figure S2 looks like a mix of sizes and shapes rather than one cell type. Is that hotspot a thicker patch of the same bacteria, or could it be a different bug?
While a cell is feeding, the anterior flagellum is attached and the posterior one beats in the groove, so I would not expect two cells to share one spot without those flagella crossing. Figure 6 puts neighboring Jakoba about a body length apart. Do they ever get closer than that, drop their flagella, and clump, or does the spacing stay?
Very cool work!
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