Rapid turnover of tissue nitrogen of primary consumers in tropical freshwaters

Abstract

Stable isotopes are widely used as time-integrating tracers of trophic interactions, but turnover rates of isotopes in animal tissues remain poorly understood. Here, we report nitrogen (N) isotope turnover rates in tissues of four primary consumer species: Ancistrus triradiatus armored catfish (muscle, fins, and whole blood), Tarebia granifera snails (muscle), and Rana palmipes tadpoles (muscle) from a Venezuelan river, and Lavigeria grandis snails (muscle) from Lake Tanganyika, East Africa. Turnover was estimated from the dilution of a 15N label introduced into consumer tissues by feeding on 15N-enriched periphyton. Muscle turnover rates were rapid (0.5-3.8% per day), and were attributable to metabolic replacement of N as well as growth in catfish and snails. N turnover in catfish muscle decreased with size, and fin tissue turned over more rapidly than whole blood or muscle, though the difference was not significant. Our results indicate that stable isotope signatures of these tropical species could change markedly within weeks following a shift in diet. However, generalization across taxa or latitudes is complicated by the strong size-dependence of isotope turnover rates. The enrichment-dilution approach outlined here may facilitate measurement of isotopic turnover in a wide variety of consumers under field conditions.

Stable carbon and nitrogen incorporation in blood and fin tissue of the catfish Pterygoplichthys disjunctivus (Siluriformes, Loricariidae)

“…In conclusion, this study is one of the first to show that fractions of blood-plasma solutes and RBCscan be used as non-lethally sampled tissues for stable isotopic analyses in fish, and is one of a few to estimate isotopic turnover rates of fin tissue (Suzuki et al 2005;McIntyre and Flecker 2006). The results show the importance of estimating turnover times and discrimination factors in the laboratory before gathering data in the field.…”

“…However, recent investigations have shown that "non-lethally" sampled tissues, such as fin (Suzuki et al 2005) or mucus (Church et al 2009), can also be used for stable isotopic analyses of fish populations. Blood, which can also be sampled non-lethally from many fish species, has heretofore been used sparingly in fish stable isotopic investigations (e.g., McIntyre and Flecker 2006). This is despite the point that blood contains two "tissues" (red blood cells and plasma/serum) that turnover at different rates (Seminoff et al 2007;Reich et al 2008), providing important comparative data for understanding dietary variation over time (Perga and Gerdeaux 2005).…”

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…Other studies have, however, revealed that considerable differences in turnover rates can be apparent between fish tissues (Buchheister & Latour, 2010;Xia et al, 2013b), although their differences are often only minor (Hesslein et al, 1993;Sweeting et al, 2005;McIntyre & Flecker, 2006). Thus, tissue turnover differentiation, as well as the relative ordering of turnover rates among tissues, appears to be speciesspecific.…”

“…Turnover rates also differ between fish species and between different tissues of individual species (e.g. McIntyre & Flecker, 2006;Church et al, 2009;Carleton & Del Rio, 2010). Rather than relying on data collected in the wild, an alternative approach is the use of experimental diet-switch studies completed in controlled conditions (Heady & Moore, 2013;Xia et al, 2013a, b;Busst & Britton, 2016).…”

Importance of terrestrial subsidies for estuarine food webs in contrasting East African catchments

“…Since most fish captured in the present study were small growing juveniles, given the time lag between the end of the 2009/2010 wet season and the pre-wet sampling (;7 months), and between the beginning of the 2010/2011 wet season and the post-wet sampling period (;6 months), any seasonal change in ultimate sources of nutrition should be reflected on consumer stable isotope composition. For small aquatic invertebrates, half-lives are much shorter, and large shifts in stable isotope composition can be detected within weeks of a change in diet (McIntyre andFlecker 2006, Dubois et al 2007). If material transported from the catchment with the flood waters is important for estuarine food webs, then we would expect seasonal differences in importance of terrestrial organic matter for animal nutrition, which should agree with the type of surrounding vegetation (C3 vs. C4) and/or land use at each site.…”