Waterbugs (Heteroptera: Nepomorpha and Gerromorpha) as sources of essential n‐3 polyunsaturated fatty acids in Central Siberian ecoregions

Abstract

Summary Aquatic systems are considered to be a main source of essential long‐chain n‐3 polyunsaturated fatty acids (PUFA), which are preferentially synthesized by microalgae and transferred along food chains to terrestrial consumers. Emerging aquatic insects comprise a significant part of this transfer of the essential PUFA from water to land. Quantitative data on PUFA content and composition are available mainly for rheophilic insects while taxa that are characteristic of wetlands and stagnant water bodies, such as aquatic Heteroptera, remain relatively unstudied. We investigated the role of various waterbug taxa (Heteroptera: Nepomorpha and Gerromorpha) inhabiting different ecoregions in temperate Central Siberia (Russia) as potential sources of PUFA. The ecoregions were steppe, forest‐steppe, hemiboreal forest and montane coniferous forest. Although these waterbugs insects are aquatic in both larval and adult stages, they can disperse through the landscape and transfer essential PUFAs from water to land so making them potentially available to terrestrial consumers. Species of Naucoridae, Notonectidae and Corixidae were generally dominant in all ecoregions, attaining maximum biomass in the steppe. We showed that habitat or ecoregion played a major role in the variability of fatty acid composition of Notonectidae and Gerridae but not Corixidae. In contrast, the biochemical composition of the only naucoridae, Ilyocoris cimicoides, was largely affected by life stage. Both the dominant families and species within them differed with respect to their mass‐specific contents of essential long‐chain PUFA of the n‐3 family, namely eicosapentaenoic and docosahexaenoic acids. Corixid species had the highest content of these two essential PUFAs among the waterbug studies, and relative to literature reports for other aquatic insects. Corixids thus appear to be a potentially important vector for transfer of the essential biochemical compounds from water to land, especially in steppe ecoregions with numerous ephemeral water bodies.

Subsidies of long‐chain polyunsaturated fatty acids from aquatic to terrestrial environments via amphibian emergence

“…EPA was lower but DHA and ARA were higher in amphibians compared to Gammaridae, Ephemeropera, Trichoptera, and Chironomidae sampled from the Yenisei River, Siberia, Russia (Sushchik et al., ). ARA and DHA were within the ranges reported for Gerridae, Naucoridae, and Corixidae from central Siberia (Sushchik et al., ). We hesitate to make direct comparisons between these strikingly different environments and taxa, but there is a dearth of fatty acid compositional information in the literature for amphibians.…”

“…Omnivory by tadpoles may at least partially explain why anurans had significantly higher levels of LC‐PUFAs than salamanders. Salamanders are predators, and would consequently be expected to bioaccumulate LC‐PUFAs due to the low degree of modification and high selective retention and trophic transfer efficiency (Gladyshev, Sushchik, et al., ; Iverson, ), although whole‐body content of ARA, EPA, and DHA are not always related to trophic position (Heissenberger, Watzke, & Kainz, ; Hixson et al., ; Sushchik et al., ). Many larval anuran taxa are often characterised as grazers and primary consumers, but there is increasing evidence of omnivory among tadpoles (Altig, Whiles, & Taylor, ; Whiles et al., ).…”

“…Total export of EPA+DHA from the aquatic ecosystem by amphibians in our study was greater than values reported for three anurans emerging from a Russian lake (1.47 mg/m 2 ; Yermokhin et al., ). Amphibians exported LC‐PUFAs to the terrestrial ecosystem at levels comparable to aquatic insect emergence in several systems (Borisova et al., ; Gladyshev, Kharitonov, et al., ; Gladyshev, Sushchik, Yurchenko, et al., ), but the amount of EPA, DHA, and ARA exported from aquatic systems may be driven by the community composition of emerging taxa, and hydroperiod (Martin‐Creuzburg, Kowarik, & Straile, ; Moyo et al., ; Sushchik et al., , ). The importance of emerging aquatic insects for riparian predators has been well documented (as reviewed by Baxter et al., ; Richardson, Zhang, & Marczak, ).…”

“…Furthermore, subsidy quality and impact is not driven only by caloric content, macronutrient amounts or ratios, or refractory materials, but also the presence of essential organic compounds and consumers’ ability (or lack thereof) to synthesise the compounds from biochemical precursors (Brett et al., ; Karasov & Del Rio, ; Twining, Brenna, Hairston, & Flecker, ; Warne, ). However, most studies have focused on the transport of bulk nutrients such as nitrogen (N) and phosphorous (P) (Anderson & Polis, ; Capps, Berven, & Tiegs, ; Fritz & Whiles, ; Hogg & Morton, ; Jonsson & Jonsson, ), whereas the flux of critical nutrients such as long‐chain polyunsaturated fatty acids (LC‐PUFAs: at least double bonds and ≥20 carbon atoms) has received less attention (but for a comprehensive list see: Borisova, Makhutova, Gladyshev, & Sushchik, ; Gladyshev, Kharitonov, et al., ; Gladyshev, Sushchik, & Makhutova, ; Gladyshev, Sushchik, Yurchenko, Belevich, & Kalacheva, ; Moyo, Chari, Villet, & Richoux, ; Sushchik et al., ; Yermokhin et al., ).…”

“…The direct consumption of aquatic prey such as fish and invertebrates by terrestrial predators such as water birds (Gladyshev et al., ) and certain mammals (Koussoroplis et al., ) provides a vector for export of LC‐PUFAs from aquatic to terrestrial food webs. Another mechanism of transport may be post‐metamorphic emergence of animals with complex life cycles such as insects and amphibians (Borisova et al., ; Gladyshev, Arts, & Sushchik, ; Gladyshev, Kharitonov, et al., ; Gladyshev, Sushchik, Yurchenko, et al., ; Lam et al., ; Moyo et al., ; Sushchik et al., ; Yermokhin et al., ). For example, riparian swallows (Hirundinidae) and raccoons ( Procyon lotor ) obtained 41% and 48% of their energy, respectively, from aquatic primary producer pathways (Kautza & Sullivan, ).…”