Changes in carbon and nitrogen stable isotopes of chironomid larvae during growth, starvation and metamorphosis

Abstract

We conducted experiments to determine isotope changes in the deposit-feeding chironomid larvae Chironomus acerbiphilus during feeding, starvation and metamorphosis. Isotope changes in chironomid larvae occurred mainly during growth and rarely afterward. This finding indicates that chironomid isotope turnover mainly occurs in conjunction with growth and suggests that chironomid larvae only break down newly assimilated food for energy during periods of no growth. Chironomid delta(13)C values significantly increased throughout the starvation experiment, indicating that chironomids preferentially break down components with lower delta(13)C content during starvation. We found significant changes in chironomid isotope ratios ((15)N enrichment) during pupation. This evidence suggests that the physiological condition of animals (such as during an active growth phase or pre- or post-molting) is important to their stable isotope ratios.

15N/14N ratios of amino acids as a tool for studying terrestrial food webs: a case study of terrestrial insects (bees, wasps, and hornets)

“…For wasps, after the egg hatches, they feed mainly on caterpillars (hunted by adult worker wasps) during their larva stage, and do not feed during metamorphose in cocoons during their chrysalis stage (e.g., Takamizawa 2005). In a previous study on the Diptera Chironomus acerbiphilus (Doi et al 2007), metamorphosis resulted in an increase of between 0.7 and 1.6& in d 15 N values of bulk tissues from larva to adult. Similar increases in d 15 N values have been observed for Lepidoptera (McCutchan et al 2003;Tabbets et al 2008) and Neuroptera (Patt et al 2003).…”

Stable isotope addition reveals dietary importance of phytoplankton and microphytobenthos to saltmarsh infauna

“…Consumers with a larger body size are expected to reach tissue equilibrium more slowly than smaller organisms and may assimilate less 15 N label over a shortterm (14 d) experiment such as ours. We based our assumption of tissue equilibrium on the larger size but high level of enrichment in Nereis diversicolor during the experiment (mudflat; see Table 2) and rapid tissue turnover times reported (Doi et al 2007) for both C and N in deposit-feeding chironomids of a mass similar to the annelids studied here. In the Doi et al 2007 study, isotope equilibrium was reached at 12 d. To determine source contributions in the enrichment model, we used the natural abundance δ 13 C values averaged over the 21 d experiment plus δ E .…”

“…We based our assumption of tissue equilibrium on the larger size but high level of enrichment in Nereis diversicolor during the experiment (mudflat; see Table 2) and rapid tissue turnover times reported (Doi et al 2007) for both C and N in deposit-feeding chironomids of a mass similar to the annelids studied here. In the Doi et al 2007 study, isotope equilibrium was reached at 12 d. To determine source contributions in the enrichment model, we used the natural abundance δ 13 C values averaged over the 21 d experiment plus δ E . Sources were spatially distinct among habitats, and we therefore varied the primary producers used in mixing models depending on habitat.…”

Linking aboveground and belowground food webs through carbon and nitrogen stable isotope analyses

“…Because the trophic enrichment factor is key to determining consumer trophic level (Gannes et al 1997), many laboratory experiments have sought to identify potential factors that can affect trophic enrichment. These studies have shown that developmental stage (Doi et al 2007), quality of diet items (Oelbermann and Scheu 2002), diet isotopic ratios (Caut et al 2008), and type of body tissues used for the analyses (DeNiro and Epstein 1978;Tieszen et al 1983) can influence enrichment factors. Meta-analyses have demonstrated that taxon, the associated biochemical form of excreted N, and feeding habits are also important determinants of trophic enrichment (McCutchan et al 2003;Vanderklift and Ponsard 2003;Caut et al 2009).…”