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Species-Specific Feeding Patterns Of Corixids (Hemiptera: Corixidae) As Indicated By Stable Isotope Analysis Stephen Srayko, Iain Phillips,Tim Jardine and Doug Chivers Outline ■ Introduction Corixid Ecology and Diet Stable Isotope Analysis Objectives ■ Methods ■ Results and Discussion Species Composition Isotopic Signatures Source Proportion Estimates Trophic Position Estimates Future Work ■ Conclusion Introduction: Corixid Ecology and Diet ■ Diverse family of aquatic Hemiptera >130 species in North America (Brooks and Kelton, 1967) ■ Wide range of aquatic habitats (Brooks and Kelton, 1967) ■ Potential for a variety of feeding strategies (Stonedahl and Lattin, 1986) Male corixid foretarsi (pala) ■ Knowledge so far: observational studies, gut content analyses Stable Isotope Analysis δ= heavy:light isotope/standard, in ‰ ■ δ13C : reflects carbon sources at food web base Δδ13C = 0.4 ‰ (Post, 2002) Pelagic vs benthic δ13C ■ δ15N : can be used to infer trophic position Δδ15N= 3.4 ‰ (Post, 2002) Hart and Lovvorn 2002 Objectives ■ To determine feeding patterns among different corixid species ■ Compare corixid δ13C and δ15N to primary consumer baselines: zooplankton=pelagic sources chironomids=benthic sources ■ δ13C: carbon source pathways ■ δ15N: trophic positions Methods: Sample Collection ■ Study sites: wetlands near Saskatoon, Saskatchewan Sample period: Aug 13-18, 2014 Saskatoon, SK ■ Corixids: D-net ■ Chironomids: D-net, Ekman dredge ■ Zooplankton: Wisconsin net Methods: Sample Processing ■ Corixids: identified to species ■ Chironomids: representative samples to genus or species ■ Zooplankton: phototaxis (Burian et al. 2014) ■ All samples: frozen ■ Stable isotope sample prep: dried at >50oC for 24 hrs, ground up, weighed and packed Methods: Data Analysis ■ Lipid correction and extraction (Braun et al., 2014; Smyntek et al. 2007) ■ Carbon source proportions: Stable Isotope Analysis in R (SIAR) (Parnell et al. 2010) ■ Trophic position: -Site specific values: SIAR source proportions, mixing model (Post, 2002) Δδ15N = 1.9 (Bunn et al., 2013) ■ Comparisons between species, and within species, between sites: 1-way ANOVAs Results and Discussion: Species Id Number Collected 350 300 250 200 150 100 50 0 ■ Chironomids: Mostly Chironomus plumosus, also Glyptotendipes sp ■ Notonectids: Notonecta borealis, N. kirbyi, N. undulata Male Female Isotope Values 12 Callicorixa audeni 11 Cenocorixa bifida Cenocorixa dakotensis 10 Cymatia americana δ15N 9 Hesperocorixa atopodonta 8 Hesperocorixa vulgaris Sigara bicoloripennis 7 Sigara decoratella 6 Notonecta borealis Notonecta kirbyi 5 Notonecta undulata 4 Chironomid 3 Zooplankton -36 -34 -32 -30 δ13C -28 ■ Average isotope values from all sites ± 1SD -26 -24 Baseline Isotope Values 12 10 y = 0.0076x2 + 0.3838x + 11.846 R² = 0.0456 δ15N 8 6 Zooplankton 4 Chironomids 2 0 -45 -40 -35 -30 δ13C -25 -20 -15 Source Proportion Estimates Proportion of Benthic Carbon ■ Mix of pelagic (POM), benthic (periphyton, detritus) pathways ■ More reliance on benthic (variable between sites) ■ H. atopodonta: complete pelagic reliance 1.2 1 0.8 0.6 0.4 0.2 0 Source Proportion Estimates ■ More reliance on benthic sources (variable between sites) ■ Benthic algae feeding: energy efficient, nutritious (Hecky and Hesslein, 1995; Bjorn and Winkelmann 2013) ■ Collectors: feed on benthic ooze: protozoa, metazoa, plant, animal material (Hungerford, 1917) ■ Predatory feeding: bottom trawl (Popham et al.1984) Trophic Position Estimates ■ Most species intermediate between primary consumer (trophic level=2) and secondary consumer (trophic level=3) positions 4 Trophic Level 3.5 3 2.5 2 1.5 1 0.5 0 Feeding Patterns Predation ■ Cymatia americana, Notonecta: predatory (Brooks and Kelton, 1967; Reynolds, 1975; Popham et al., 1984) ■ Low trophic fractionation in predatory invertebrates -High nitrogen use efficiency (Vanderklift and Ponsard, 2003; Cremona et al. 2010) ■ Suctorial predators: low trophic fractionation e.g. Cremona et al. 2010 δ15N values of different feeding groups: 1o Consumers= 8.31‰ Predators (all)= 9.53‰ Predators- suckers= 7.96‰ Cymatia americana pala (top) Feeding on chironomid (bottom) Feeding Patterns Omnivory ■ Assimilation of algal carbon in predatory taxa (Lancaster et al., 2005) ■ Feeding plasticity: adaptation to resource availability, important in variable habitat conditions (Bjorn and Winkelmann, 2013; Zah et al., 2001) ■ High overlap in δ15N signatures: possible lack of distinct trophic levels, generalist feeding (Beaudouin et al., 2001) Fry 1991 Future Work ■ Gut content analysis: gel electrophoresis (Giller, 1986) ■ Lab studies: -Rearing study: turnover rate, effects of development, corixid specific trophic fractionation factor (Ostrom et al. 1977; Tibbets et al. 2008; Jardine et al. 2008) -food choice experiments (Klecka, 2014) Conclusion ■ Corixid feeding patterns: variable within and between species ■ Mix of benthic/pelagic carbon source pathways, tending towards benthic sources ■ Potentially high prevalence of omnivory across different species ■ Widespread presence of corixids in different aquatic habitats possibly related to ability to utilize a variety of food resources Thanks! Stephen Srayko University of Saskatchewan [email protected] Special thanks to: Water Security Agency, Saskatoon Alix Schmidt Iona Tangri Dale Parker Myles Stocki