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Abstract Microbial eukaryotes, critical links in aquatic food webs, are unicellular, but some, such as choanoflagellates, form multicellular colonies. Are there consequences to predator avoidance of being unicellular vs. forming larger colonies? Choanoflagellates share a common ancestor with animals and are used as model organisms to study the evolution of multicellularity. Escape in size from protozoan predators is suggested as a selective factor favoring evolution of multicellularity. Heterotrophic protozoans are categorized as suspension feeders, motile raptors, or passive predators that eat swimming prey which bump into them. We focused on passive predation and measured the mechanisms responsible for the susceptibility of unicellular vs. multicellular choanoflagellates,Salpingoeca helianthica, to capture by passive heliozoan predators,Actinosphaerium nucleofilum, which trap prey on axopodia radiating from the cell body. Microvideography showed that unicellular and colonial choanoflagellates entered the predator's capture zone at similar frequencies, but a greater proportion of colonies contacted axopodia. However, more colonies than single cells were lost during transport by axopodia to the cell body. Thus, feeding efficiency (proportion of prey entering the capture zone that were engulfed in phagosomes) was the same for unicellular and multicellular prey, suggesting that colony formation is not an effective defense against such passive predators.
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Fluid mechanics of feeding determine the trophic niche of the hydromedusa Clytia gregaria
Abstract Phenotypic features define feeding selectivity in planktonic predators and therefore determine energy flow through food webs. In current‐feeding cnidarian hydromedusae, swimming and predation are coupled such that swimming also brings prey into contact with feeding structures. Fluid mechanical disturbances may initiate escape responses by flow‐sensing prey. Previous studies have not considered how fluid signals define the trophic niche of current‐feeding gelatinous predators. We used the hydromedusaClytia gregariato determine (1) how passive (sinking) and active (swimming) feeding behavior affects pre‐encounter responses of prey to the medusae‐induced fluid motion, and (2) how prey responses affect the medusae's ingestion efficiencies. Videography of the predation process showed that passive prey such as invertebrate larvae were ingested during both feeding behaviors, whereas flow‐sensing prey such as copepods escaped the predator's active feeding behavior, but were unable to detect the predator's passive sinking behavior and were ingested (KWX2= 19.8246, df = 4,p < 0.001). Flow visualizations using particle image velocimetry (PIV) showed fluid deformation values during passive feeding below threshold values that trigger escape responses of copepods. To address whether fluid signals mediate prey capture, we compared fluid signals produced by three hydromedusae with different diets.Aequorea victoriaandMitrocoma cellulariaproduced higher deformation thanC. gregaria(two‐way ANOVA,F2,52= 5.532,p= 0.007), which explains their previously documented negative selection for flow‐sensing prey like copepods. Through the analysis of hydromedusan feeding behaviors and pre‐encounter prey escapes, we provide evidence that fluid signatures shape the trophic niches of gelatinous predators.
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- Award ID(s):
- 1737364
- PAR ID:
- 10444142
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Limnology and Oceanography
- Volume:
- 66
- Issue:
- 3
- ISSN:
- 0024-3590
- Page Range / eLocation ID:
- p. 939-953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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