Lipid content and carbon assimilation in Collembola: implications for the use of compound-specific carbon isotope analysis in animal dietary studies

Abstract

In an effort to understand the relationships between both the lipid content and delta13C values of Collembola and their diet, isotopically labelled (C3 and C4) bakers' yeasts were cultured and fed to two Collembolan species, Folsomia candida and Proisotoma minuta. The fatty acid composition of Collembola generally reflected that of the diet with the addition of the polyunsaturated components 18:2(n-6), 20:4(n-6) and 20:5(n-3), which appeared to be biosynthesised by the Collembola. Whilst ergosterol was the only sterol detected in the yeast diets, only cholesterol was detected in Collembola, and although the delta13C values of diet and consumer sterols differed by >2 per thousand, the delta13C values indicated that cholesterol was derived entirely from dietary sterol. The bulk delta13C values of Collembola were similar to those of the diets, but fatty acid delta13C values did not necessarily reflect those of the dietary fatty acids, indicating significant de novo biosynthesis of fatty acids within Collembola. Switching the Collembola from C3 to C4 yeast enabled the determination of the rates of incorporation of dietary carbon into Collembolan lipids, and showed that half-lives of the incorporation of dietary carbon varied between 1.5 and 5.8 days at 20 degrees C. Cholesterol exhibited the slowest rate of incorporation in both species, while bulk carbon in F. candida possessed an intermediate rate. These results demonstrate that an understanding of the sources of isotopic fractionation and the role of biochemistry in regulating the delta13C values of individual compounds is important in the application of compound-specific isotopic analysis to the study of animal trophic activities.

Changes in δ 13C stable isotopes in multiple tissues of insect predators fed isotopically distinct prey

“…This variation has been used to infer changes in diets in migratory birds over a time period of 2-3 weeks (Podlesak et al 2005). In contrast, studies of invertebrates, such as beetles, springtails, and moths, have often found rapid changes in isotope values (5-10 days for 75% isotope change) in whole-body assays (Ostrom et al 1997) as well as more specific fractions (Chamberlain et al 2004;O'Brien et al 2000, this study). It remains to be seen if there are any tissues within arthropods that reflect dietary intake over longer periods (e.g., months).…”

“…Interpreting patterns of stable isotopes in consumers to determine diet sources requires an understanding of the isotopic signature of potential food items, how those molecules fractionate once they are assimilated, and how isotopes become incorporated into different tissues over time. Laboratory experimentation needed for interpreting isotopes' patterns has advanced rapidly in vertebrate systems (Ayliffe et al 2004;Hobson and Clark 1992;Ogden et al 2004;Tieszen et al 1983) and is increasing in intensity for invertebrates (Chamberlain et al 2004;Oelbermann and Scheu 2002;Ostrom et al 1997;Rothe and Gleixner 2000;Ruess et al 2004;Scheu and Folger 2004) although few studies have examined isotope changes in more than one tissue (Webb et al 1998). …”

Nutritional importance of minor dietary sources for leaping grey mullet Liza saliens (Mugilidae) during settlement: insights from fatty acid δ13C analysis

“…Nevertheless, essential FAs are not always specific, as they can be simultaneously present in more than one source, hence limiting their value as biomarkers. However, by characterizing these compounds isotopically (compoundspecific isotopic analysis [CSIA]), it is possible to determine whether all essential FAs have common or distinct sources, and also to obtain specific information on their origins (Murphy & Abrajano 1994, Pond et al 1997a,b, Rieley et al 1999, Chamberlain et al 2004, Van den Meersche et al 2009). Moreover, the rapid isotopic turnover of FAs compared to other biochemical fractions makes analysis of their δ 13 C a very reactive proxy for fast dietary change (Meier-Augenstein 2002, Lau et al 2009).…”

Thresholds for Sterol-Limited Growth of Daphnia magna: A Comparative Approach Using 10 Different Sterols

“…Besides dihydrocholesterol (Δ 0 ) and cholesterol (Δ 5 ), comparatively The different conversions may involve additional intermediate products not shown here. For instance, the conversion of C28 sterols, such as 22-dihydrobrassicasterol, to desmosterol presumably involves the formation of a Δ 24,(28) double bond to yield 24-methylenecholesterol and subsequently the formation of an epoxide prior to the loss of the C24 methyl group as it is found in various insects and decapod crustaceans (Chamberlain et al 2004;Ikekawa et al 1993;Kanazawa 2001;Svoboda 1999). Likewise, epoxidation prior to the actual dealkylation process is expected to be involved in the conversion of C29 sterols, such as stigmasterol or sitosterol, to desmosterol.…”