Trophic Discrimination Factors of Stable Carbon and Nitrogen Isotopes in Hair of Corn Fed Wild Boar

Abstract

Stable isotope measurements are increasingly being used to gain insights into the nutritional ecology of many wildlife species and their role in ecosystem structure and function. Such studies require estimations of trophic discrimination factors (i.e. differences in the isotopic ratio between the consumer and its diet). Although trophic discrimination factors are tissue- and species- specific, researchers often rely on generalized, and fixed trophic discrimination factors that have not been experimentally derived. In this experimental study, captive wild boar (Sus scrofa) were fed a controlled diet of corn (Zea mays), a popular and increasingly dominant food source for wild boar in the Czech Republic and elsewhere in Europe, and trophic discrimination factors for stable carbon (Δ13C) and nitrogen (Δ15N) isotopes were determined from hair samples. The mean Δ13C and Δ15N in wild boar hair were –2.3 ‰ and +3.5 ‰, respectively. Also, in order to facilitate future derivations of isotopic measurements along wild boar hair, we calculated the average hair growth rate to be 1.1 mm d-1. Our results serve as a baseline for interpreting isotopic patterns of free-ranging wild boar in current European agricultural landscapes. However, future research is needed in order to provide a broader understanding of the processes underlying the variation in trophic discrimination factors of carbon and nitrogen across of variety of diet types.

Case Study: Atypical δ13C values of urinary norandrosterone

“…[21][22][23][24] According to these studies, δ 13 C values for mammalian hair of −15 ‰ can be attributed to an almost completely corn-based diet. 21,22,24 On the other hand, δ 13 C values of −24 ‰ and lower are attributed to exclusively C 3 -plants in the diet. 21,22,24…”

“…7 The endogenous-like carbon isotopic signature of urinary NorA after consumption of "castrated pig edible parts" was reported in the past, although no δ 13 C values were presented proving the validity of this statement. 24 The bristles analyzed showed that several months before, the dietary source of the animal had been completely different, with δ 13 C values of −24 ‰ and thus without a major contribution of corn in the diet. This has been determined, for example, using hair [25][26][27][28][29][30] was shot mid-January 2018, thus plausibly matching the carbon isotopic signature of an animal that was completely fed on corn.…”

“…The growth rate for wild boars bristles is about 1.1 mm per day, 24 leading to a time span of approximately three months being covered FIGURE 1 Retrospective analysis of the wild boar's diet by EA-IRMS of the boar's bristles. The first 40 mm (youngest part) is clearly dominated by C4-plants (corn) in the diet, whereas the older segments (>45 mm) represent an almost exclusive C3-forage by the analyzed bristles.…”

“…different bristles with lengths of 60 and 70 mm were analyzed per EA-IRMS. According to these studies, δ 13 C values for mammalian hair of −15 ‰ can be attributed to an almost completely corn-based diet 21,22,24. Younger segments close to the skin yielded the most enriched δ 13 C values compared to segments from the bristle tips.The results supported the conclusion that at some point a complete change of the boar's primary forage occurred.…”

“…It is known that the δ 13 C values of mammalian (and human) body protein, either hair keratin or muscle protein, rapidly adapts towards a change in the 13 C content of the diet [21][22][23][24]. δ 13 C values ranged from −14.5 ‰ to −23.8 ‰ (Figure 1).…”