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

摘要

Anthropogenic stressors can affect the emergence of aquatic insects. These insects link aquatic and adjacentterrestrial food webs, serving as high‐quality subsidy to terrestrial consumers, such as spiders. While previous studies havedemonstrated that changes in the emergence biomass and timing may propagate across ecosystem boundaries, thephysiological consequences of altered subsidy quality for spiders are largely unknown. We used a model food chain to studythe potential effects of subsidy quality: Tetragnatha spp. were exclusively fed with emergent Chironomus riparius cultured inthe absence or presence of either copper (Cu), Bacillus thuringiensis var. israelensis (Bti), or a mixture of synthetic pesticidespaired with two basal resources (Spirulina vs. TetraMin?) of differing quality in terms of fatty acid (FA) composition. Basalresources shaped the FA profile of chironomids, whereas their effect on the FA profile of spiders decreased, presumably dueto the capacity of both chironomids and spiders to modify (dietary) FA. In contrast, aquatic contaminants had negligibleeffects 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 mayhave contributed to the statistically significant decline (40–50) in spider growth. The observed effects in spiders are likelyrelated 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 thataquatic contaminants can affect the physiology of riparian spiders, likely by altering subsidy quality, with potential implicationsfor terrestrial food webs.