Stream grazers determine their crawling direction on the basis of chemical and particulate microalgal cues

Abstract

This study aimed to determine the association between herbivore behavior and cues from producers. We used stream grazer Glossosoma larvae and determined their crawling direction in relation to chemical and visual cues from microalgae. The experimental treatments included control (no cue), particulate (chemical and particulate cues), and dissolved (chemical cue) cues from microalgae. The experimental water samples were randomly placed into either arm of a Y-shaped channel, and the crawling direction of the grazers was determined. Although the grazers crawled toward the arm containing either particulate or dissolved cues, they preferred the arm with particulate cues. This suggested that grazers responded well to both particulate (i.e., drifting algal cells) and chemical (algal smell) cues, and that particulate cues were more important for foraging. In natural habitats, grazers detect cues from producers and change their behaviors to maintain a balance between top-down and bottom-up cues.

Increased reliance of stream macroinvertebrates on terrestrial food sources linked to forest management intensity

“…Another solution was to use isotopic values of herbivores as proxies for the isotopic values of algae (Vander Zanden and Rasmussen , Finlay ), and we used the ubiquitous Glossosoma scrapers, which are known to selectively feed on the algal portion of biofilms (Oemke , McNeely et al. , Katano and Doi ), to reflect algal δ 13 C and δ 15 N. We acknowledge that this approach may have introduced some error in our estimates as it assumes 100% herbivory by Glossosoma across streams. That assumption is unlikely to be true, leading to an overestimation of autochthonous contributions.…”

“…To improve source separation, we first incorporated a third marker (d 2 H), since the addition of H isotopes to stream food web studies has been shown to increase the resolution of dietary sources (Doucett et al 2007, Jardine et al 2009, Finlay et al 2010), but the source overlap remained. Another solution was to use isotopic values of herbivores as proxies for the isotopic values of algae Rasmussen 1999, Finlay 2001), and we used the ubiquitous Glossosoma scrapers, which are known to selectively feed on the algal portion of biofilms (Oemke 1984, McNeely et al 2006, Katano and Doi 2014, to reflect algal d 13 C and d 15 N. We acknowledge that this approach may have introduced some error in our estimates as it assumes 100% herbivory by Glossosoma across streams. That assumption is unlikely to be true, leading to an overestimation of autochthonous contributions.…”

“…A potential solution for obtaining the isotopic value of primary producers is to use values of herbivores as proxies Rasmussen 1999, Finlay 2001). We estimated algal d 13 C and d 15 N from Glossosoma because this genus (1) had consistently the most negative d 13 C values, (2) was present in every stream, and (3) is known to feed selectively on microscopic algae on biofilms (Oemke 1984, McNeely et al 2006, Katano and Doi 2014. d 2 H values of algae were estimated by subtracting 170& AE 15& from stream water d 2 H, based on studies showing that primary producers fractionate against 2 H during photosynthesis, resulting in 160-170& more negative values than environmental water (Yakir and DeNiro 1990, Solomon et al 2011, Hondula et al 2014.…”

Effects of stream grazers with different functional traits on the spatial heterogeneity of periphyton mats

“…Periphytic algae are the most important primary producers in stream ecosystems (Minshall, 1978; Vannote et al, 1980; Lange et al, 2011). Grazer-periphyton interactions in stream environments have been used as model systems to understand more general producer-herbivore interactions (Hart & Robinson, 1990; Feminella & Hawkins, 1995; Doi, Katano & Kikuchi, 2006; Doi & Katano, 2008; Katano & Doi, 2014). The influence of resources and grazing on the composition of periphyton assemblages can be assessed both taxonomically and with regard to functional groups (Passy, 2008), two parameters that can be affected by light, nutrients, and grazing regimes (Johnson, Tuchman & Peterson, 1997; Hollingsworth & Vis, 2010; Lange et al, 2011).…”

Prediction of Glossosoma biomass spatial distribution in Valley Creek by field measurements and a three‐dimensional turbulent open‐channel flow model

“…The patterns of macroinvertebrate spatial distribution are governed by multiple fluid flow, biologic, geomorphic, and chemical variables acting both independently and in combination [ Statzner et al ., ; Nikora , ; Holomuzki et al ., ; Katano and Doi , ]. Among these variables, open‐channel fluid flow conditions represent a major hydraulic gradient along which the benthic macroinvertebrate community is organized [ Rempel et al ., ].…”