Contrary to a general rule of stable isotope trophic discrimination, parasites show great variation in isotope discrimination from their host muscle tissues. One of the possible mechanisms is that isotopic variation among host tissues may cause apparent deviation from the actual isotope discrimination between a parasite and a given host tissue consumed by the parasite. To test this possibility, we measured δ¹⁵N and δ¹³C for some fish parasites and a variety of their host tissues to estimate their actual trophic discrimination factors (Δ). All of the trematodes investigated showed positive Δ¹⁵Ν values and nearly zero Δ¹³C values, which are comparable to those of free-living consumers. Cestodes and nematodes showed great variations in their Δ¹⁵Ν and Δ¹³C values when they were compared to a particular tissue/mucus of their infection site. Acanthocephalans showed negative Δ¹⁵Ν and Δ¹³C values in comparison with host intestinal mucus, and a crustacean had δ values similar to those of host blood. Even in parasites infected to intestine, Δ¹⁵Ν and Δ¹³C values varied among higher taxa. These results suggested that atypical ¹⁵N and ¹³C enrichment of parasites is not caused by the variation in δ values among host tissues, but possibly by metabolic processes unique to each parasite taxon.

中文翻译：

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寄生虫中非典型的15 N和13 C富集是否是由它们感染的宿主组织的同位素比率变化引起的吗？

与稳定同位素营养鉴别的一般规则相反，寄生虫显示出从其宿主肌肉组织中同位素鉴别的巨大变化。可能的机制之一是宿主组织之间的同位素变化可能导致明显偏离寄生虫与该寄生虫消耗的给定宿主组织之间的实际同位素区分。为了测试这种可能性，我们测量δ ¹⁵ N和δ ¹³ ℃下一些鱼类的寄生虫和各种它们的宿主组织的估算其实际营养因子歧视（Δ）。所有吸虫的调查显示阳性Δ ¹⁵ Ν值和几乎为零的Δ ¹³C值，与自由生活的消费者相当。在他们的绦虫和线虫表现出极大的变化Δ ¹⁵ Ν和Δ ¹³当它们进行比较，以特定的组织/粘液其感染部位的C值。棘呈现负Δ ^15个Ν和Δ ¹³ C值与宿主肠粘液比较，以及甲壳纲动物有δ值类似于那些的宿主血液。即使在寄生虫感染到肠，Δ ¹⁵ Ν和Δ ¹³ C值更高类群中变化。这些结果表明非典型的¹⁵ N和¹³寄生虫的C富集不是由宿主组织之间的δ值变化引起的，而是由每种寄生虫分类群特有的代谢过程引起的。