Nitrogen stress causes unpredictable enrichments of 15N in two nectar-feeding bat species

Abstract

SUMMARY We estimated the effect of nitrogen stress on the nitrogen isotope enrichments in wing membrane and blood of two nectar-feeding bats(Glossophaga soricina and Leptonycteris curasoae) by offering a nitrogen-poor diet with a high δ15N andδ 13C. Before the experiment, bats were sustained on a normal diet with a low δ15N and δ13C. Under this first food regime, the fractionation of nitrogen isotopes averaged 3.1‰δ 15N for blood and 4.4‰ δ15N for wing membrane, which was almost twice as high as the corresponding fractionation of carbon isotopes. After switching to the nitrogen-poor diet, the enrichment of heavy isotopes increased for both elements in all tissues under study. The recently published estimates of half-life of carbon isotopes indicated a low turnover rate of carbon in wing membrane and blood and an almost constant half-life over varying losses of body mass. The estimates of half-life of nitrogen were two to six times higher than those of carbon. We argue that this discrepancy was caused by the mixing of nitrogen isotopes from internal and external sources. The mixing effect was probably negligible for carbon as the amount of ingested carbon outweighed the amount of mobilized carbon from internal sources. A correlation between the estimated turnover rates of nitrogen and losses of body masses was probably obscured by the additional fractionation of nitrogen isotopes in catabolic animals. We conclude that the interpretation of nitrogen isotope data of free-ranging animals is difficult when the animal's diet is changing to a critical nitrogen content.

Origins and migratory patterns of bats killed by wind turbines in southern Alberta: evidence from stable isotopes

“…We examined the correlations between isotope value and date for evidence of differential migration (e.g., Mazerolle and Hobson 2007, Paxton et al 2007, Langin et al 2009 (Hobson et al 1993, Kelly 2000, Voigt and Matt 2004, Smith et al 2010). Thus, it may be that bats arriving earlier in the season were either foraging at a higher trophic level, or were more water or nutritionally stressed at the time their fur was grown, than bats arriving later in the season.…”

“…Fortunately, we know the dietary ecology of hoary bats and silver-haired bats summering in Canada (Barclay 1985, Reimer et al 2010 and that diet-to-tissue discrimination in bats is similar to that for other vertebrates (Voigt et al 2003, Voigt and Matt 2004, Mirón et al 2006, PopaLisseanu et al 2007. Stable-isotope analysis of bat tissue has been used in numerous dietary studies (Fleming et al 1993, Voigt and Kelm 2006, Popa-Lisseanu et al 2007, Painter et al 2009, Cryan et al 2012, and also to investigate the origins and migratory movements of bats.…”

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

“…A good example of the effect of diet composition on isotope discrimination and turnover rate was recently reported in two species of nectarivorous bats, Glossophaga soricina and Leptonycteris curasoae (Voigt et al, 2003;Voigt and Matt, 2004). These bats were switched to an extremely low nitrogen diet (0.1%N).…”

“…Slow carbon turnover rate in bat blood was explained as a result of presumably long-lived erythrocytes (Voigt et al, 2003). In the case of nitrogen, slow turnover rates were explained as the result of the effect of the mixing of internal and external sources of nitrogen, additional fractionation of nitrogen isotopes and individual metabolic rates (Voigt and Matt, 2004).…”

“…Nectarivorous bats were fed a diet of corn syrup, cane sugar, agave syrup and Opuntia fruits in previous discrimination and turnover experiments (Voigt et al, 2003;Voigt and Matt, 2004). These diets were high in carbohydrates but extremely low in nitrogen (fruits were the main source of nitrogen and contained 0.7% nitrogen).…”