Subsidy Quality Affects Common Riparian Web‐Building Spiders: Consequences of Aquatic Contamination and Food Resource

Abstract

Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacent terrestrial food webs, serving as high‐quality subsidy to terrestrial consumers, such as spiders. While previous studies have demonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, the physiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to study the potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured in the absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticides paired with two basal resources (Spirulina vs. TetraMin®) of differing quality in terms of fatty acid (FA) composition. Basal resources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably due to the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligible effects on prey FA profiles but reduced the content of physiologically important polyunsaturated FAs, such as 20:4n‐6 (arachidonic acid) and 20:5n‐3 (eicosapentaenoic acid), in spiders by approximately 30% in Cu and Bti treatments. This may have contributed to the statistically significant decline (40%–50%) in spider growth. The observed effects in spiders are likely related to prey nutritional quality because biomass consumption by spiders was, because of our experimental design, constant. Analyses of additional parameters that describe the nutritional quality for consumers such as proteins, carbohydrates, and the retention of contaminants may shed further light on the underlying mechanisms. Our results highlight that aquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implications for terrestrial food webs. Environ Toxicol Chem 2023;42:1346–1358. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Detritivore physiology and growth benefit from algal presence during microbial leaf colonization

“…Therefore, future studies should not only focus on the impacts of autotrophic-heterotrophic interactions on energy pathways within aquatic ecosystems, but also delve into shifts in the physiology of merolimnic, detritivorous insects such as caddisflies, potentially influencing their quality as prey for riparian predators (cf. Pietz et al 2023). In this context, it seems crucial to consider biomolecules beyond FAs, such as amino acids and sterols, to obtain a more holistic understanding of the effects of food quality on consumers and the potential subsequent repercussions throughout the food web.…”

“…We conducted FA profile analyses for both the leaf litter used as food sources and the detritivore G. fossarum at the beginning and termination of the experiment. For the leaf material, we extracted lipids from lyophilized and weighed samples (26–35 mg; n = 3) using a chloroform/methanol mixture (2 : 1; v : v ) in the presence of the internal standard triacylglycerol with three deuterated 18:0 FAs, as described by Pietz et al (2023). The samples were stored at −20°C overnight, followed by lipid hydrolysis and FA methylation to obtain fatty acid methyl esters (FAMEs) using 3 N methanolic HCl (Sigma‐Aldrich) at 70°C for 20 min.…”

“…The neutral lipids were then hydrolyzed, and FAs were methylated to FAMEs using trimethylsulfonium hydroxide (Sigma‐Aldrich). Gas chromatography (GC) with flame‐ionization detection (Trace GC Ultra; Thermo Fisher Scientific), employing a Restek FAMEWAX capillary GC column (30 m × 0.25 mm, 0.25 μ m film thickness) and helium (1.4 mL min −1 ) as carrier gas, was utilized for the identification and quantification of FAMEs (Pietz et al 2023).…”

Bridging the Gaps: Exploring Aquatic–Terrestrial Connectivity through the Trait-Based Ecology of Riparian Predatory Arthropods

“…PUFAs and stoichiometric analyses promise to provide better insights into the way that riparian predatory arthropods function and should consequently receive increased attention. More research on the effects of poor nutrition on community structure and the behavioral responses of riparian predatory arthropods is also needed [115].…”