Effect of diet quality on carbon and nitrogen turnover and isotopic discrimination in blood of a New World nectarivorous bat

Abstract

SUMMARY Diet composition of carbon and nitrogen (C:N) could affect diet-tissue isotopic discrimination and elemental turnover rate in consumers but studies that test the nature of these changes are scarce. We compared carbon and nitrogen isotopic discrimination and turnover rates in individuals of Pallas'long-tongued bats Glossophaga soricina fed diets with protein soya isolate or amaranth grains as their main source of protein. Diets were of similar protein biological value but the soya diet had higher nitrogen content(2.2%N) and lower C:N ratio (39.6) than the amaranth diet (1.3%N, C:N=40.5). Most bats on the soya diet gained body mass whereas most bats on the amaranth diet lost body mass. Half-lives of carbon (24.3±3.8 days) and nitrogen(25.6±4.4 days) in bats switched to the soya diet were very similar. In contrast, in the bats switched to the amaranth diet, carbon half-life(39.7±3.4 days) was longer than that of nitrogen (25.0±6.0 days). The enrichment in 15N between diet and blood was higher when bats were fed the amaranth diet (4.4±0.2‰) than when they were fed the soya diet (3.3±0.2‰). Similarly, bats on the amaranth diet had higher 13C enrichment (2.0±0.2‰) than bats on the soya diet (0.1±0.1‰). Our results support recent hypotheses of the effect of nutrition on diet-tissue isotopic discrimination and turnover rate, and further shows that blood stable isotope analysis is an adequate approach to track seasonal dietary shifts in wild bats.

Divergent trophic levels in two cryptic sibling bat species

“…In a follow-up study to Voigt et al (2003), Miron et al (2006) found lower D 15 N values in the same nectar-feeding bat species when the animals were fed a nitrogen-rich diet. The fact that D 15 N is lower in consumers feeding on a nitrogen-rich diet might help explain the lower D 15 N of M. myotis consuming protein-rich mealworms, but it fails to explain the larger D 15 N of M. nattereri feeding on the same diet.…”

“…The stepwise enrichment of heavy in relation to light isotopes between consumer and diet is called discrimination (del Rio et al 2009) and amounts to about 3.5% for 15 N in relation to 14 N and to only 1-2% for 13 C in relation to 12 C (DeNiro andEpstein 1978, 1981). For bats, the only published data on discrimination stem from neotropical phyllostomid nectar-feeding bats (Voigt et al 2003;Miron et al 2006). As they are both phylogenetically distant and very dissimilar in feeding ecology from our study species, we conducted controlled laboratory experiments to measure the discrimination of isotopes in the tissue of one of our study species and a closely related congener.…”

The impact of protein quality on stable nitrogen isotope ratio discrimination and assimilated diet estimation

“…Thus far, current mixing models treat the assigned discrimination value for each food as a constant that is frequently determined with captive animals (e.g., Hobson and Clark 1992a;Hilderbrand et al 1996;Felicetti et al 2003;Robbins et al 2005;Caut et al 2008a). Such discrimination values vary with some characteristic of the food (e.g., protein quality or quantity) or animal (e.g., speciWc tissue, level of intake, growth rate, or metabolic rate; Fantle et al 1999;Roth and Hobson 2000;Gaye-Siessegger et al 2004;Robbins et al 2005;Miron et al 2006;Gaye-Siessegger et al 2007;Caut et al 2008a;Martinez del Rio et al 2009). …”

“…2 The relationships between the 15 N of the diet and a 15 N of the animal or b 15 N between the diet and animal for whole blood, plasma or serum of mammals and birds. The values are for when mixed diets with multiple protein sources were fed (Hobson and Clark 1992b;Hilderbrand et al 1996;Roth and Hobson 2000;Ben-David and Schell 2001;Jenkins et al 2001;Haramis et al 2001;Felicetti et al 2003;Pearson et al 2003;Ogden et al 2004;Cherel et al 2005;Arneson and MacAvoy 2005;Miron et al 2006;Darr and Hewitt 2008;Tsahar et al 2008;this study). Dashed lines are the regressions from Fig.…”

Tracing prey origins, proportions and feeding periods for predatory beetles from agricultural systems using carbon and nitrogen stable isotope analyses

“…Diet composition of carbon and nitrogen could affect diet-tissue isotopic discrimination and elemental turnover rate in consumers (Miron et al, 2006). In the dietary shift experiment, the d 13 C values in the wing and abdomen of P. japonica adults indicated that individual beetles shifting from a C 3 -to a C 4 -based diet of aphids fed on maize or cotton, respectively, would start to reflect the carbon stable isotope ratios of their new C 4 substrates within 7 days.…”