Metal Exposure and Sex Shape the Fatty Acid Profile of Midges and Reduce the Aquatic Subsidy to Terrestrial Food Webs

Abstract

Aquatic micropollutants can be transported to terrestrial systems and their consumers by emergent aquatic insects. However, micropollutants, such as metals, may also affect the flux of physiologically important polyunsaturated fatty acids (PUFAs). As certain PUFAs have been linked to physiological fitness and breeding success of terrestrial consumers, reduced fluxes from aquatic systems could affect terrestrial populations and food webs. We chronically exposed larvae of the aquatic insect Chironomus riparius to a range of environmentally relevant sediment contents of cadmium (Cd) or copper (Cu) in a 28-day microcosm study. Since elevated water temperatures can enhance metals' toxic effects, we used two temperature regimes, control and periodically elevated temperatures (heat waves) reflecting an aspect of climate change. Cd and Cu significantly reduced adult emergence by up to 95% and 45%, respectively, while elevated temperatures had negligible effects. Both metal contents were strongly reduced (∼90%) during metamorphosis. Furthermore, the chironomid FA profile was significantly altered during metamorphosis with the factors sex and metal exposure being relevant predictors. Consequently, fluxes of physiologically important PUFAs by emergent adults were reduced by up to ∼80%. Our results suggest that considering fluxes of physiologically important compounds, such as PUFAs, by emergent aquatic insects is important to understand the implications of aquatic micropollutants on aquatic-terrestrial meta-ecosystems.

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

“…Consistent with our hypothesis, sex was an important discriminating factor for the FA profiles of chironomids and spiders, explaining 13% and 16% of the total variation, respectively. The differences in the FA profiles of females and males match previous studies focusing on insects (Meier et al, 2000; Pietz et al, 2023; Scharnweber et al, 2020) but may also occur in spiders, presumably because of sex‐specific life‐history strategies. Indeed, sexual dimorphism in terms of morphology (i.e., females being larger than males) and reproductive investment strategies (i.e., energy storage in females and mating success in males) seem to be similar in both groups (Cordellier et al, 2020; Servia et al, 2006).…”

“…Indeed, contaminants in aquatic ecosystems (e.g., metals and synthetic pesticides) have been linked to the decline of aquatic insect emergence (Kraus et al, 2014; Stepanian et al, 2020) and declines in terrestrial consumers (Graf et al, 2019; Kraus et al, 2014). The latter may at least partly be attributed to reduced fluxes, and hence availability, of physiologically important nutrients (Pietz et al, 2023; Twining et al, 2019). Metals, for example, can alter the fatty acid (FA) composition and content of aquatic midges and reduce their emergent biomass (Pietz et al, 2023).…”

“…The latter may at least partly be attributed to reduced fluxes, and hence availability, of physiologically important nutrients (Pietz et al, 2023; Twining et al, 2019). Metals, for example, can alter the fatty acid (FA) composition and content of aquatic midges and reduce their emergent biomass (Pietz et al, 2023). Some of these FAs, such as the polyunsaturated FAs (PUFAs) eicosapentaenoic acid (EPA; 20:5n‐3) and arachidonic acid (ARA; 20:4n‐6), promote immune function, growth, and breeding success in terrestrial consumers (Fritz et al, 2017; Twining, Shipley, & Winkler, 2018; Twining et al, 2019).…”

“…israelensis (Bti), and a mixture of synthetic pesticides were used as model stressors because of their wide application to, or frequent detection in, freshwaters (Becker et al, 2018; Brühl et al, 2020; Feiler et al, 2013; Halbach et al, 2021). In addition, they affect the lipid profile of invertebrates (Pietz et al, 2023; Zubrod et al, 2011), or their mode of action compromises lipid membranes in the gut of nematocerous dipterans (Vachon et al, 2012). The selection of chironomids is motivated by their quantitative importance for aquatic emergence and as prey for many terrestrial consumers (Leeper & Taylor, 1998; Martin‐Creuzburg et al, 2017; Ohler, Schreiner, Link, et al, 2023; Regester et al, 2008).…”

Impact across ecosystem boundaries – Does Bti application change quality and composition of the diet of riparian spiders?

“…Vice versa, high-nutrient prey is expected to increase survival, reproductive success as well as the tolerance towards toxic substances and to accelerate juvenile growth (Mayntz and Toft, 2001). Thus, the observed temporal fluctuations in macronutrient and glycogen levels of aquatic insects and their relevance for terrestrial predators should be addressed furtherparticularly in situations in which disturbances in aquatic systems are affecting besides the quantity also the quality of this subsidy (Pietz et al, 2023).…”