Blood-specific isotopic discrimination factors in the Magellanic penguin (Spheniscus magellanicus)

Abstract

Having an accurate discrimination factor for the studied species is key in any trophic or food web isotopic study. Comparisons of estimated diet-to-blood discrimination factors with published values of aquatic piscivore birds showed that the (13) C discrimination factor is particularly variable, and therefore ecologists should be cautious when using a surrogate value from other species. In this study, the Magellanic penguin discrimination factor of a tissue that does not require euthanasia was obtained, a fundamental input for trophic isotopic modeling of the species. Copyright © 2016 John Wiley & Sons, Ltd.

Diet–tissue discrimination factors (δ15N and δ13C values) for blood components in Magellanic (Spheniscus magellanicus) and southern rockhopper (Eudyptes chrysocome) penguins

“…DTDFs were calculated separately for each species, blood component, and prey tissue type for δ 13 C and δ 15 N values (Table ). For both Magellanic and southern rockhopper penguins, our CC Δ 13 C values (1.22 ± 0.03, 1.26 ± 0.03) were higher than the whole blood values of those species from published studies (0.41 ± 0.12, −0.81), while our CC Δ 15 N values (2.54 ± 0.07, 2.43 ± 0.17) were similar (2.31 ± 0.17, 2.72; Table ). In contrast, our plasma Δ 13 C values (−0.63 ± 0.49, −0.27 ± 0.22) were lower than those from published studies on whole blood, while the Δ 15 N values were similar (2.60 ± 0.50, 2.78 ± 0.22; Table ).…”

“…Proper sample storage is important to eliminate biases of tissue decomposition, which affect δ 15 N and δ 13 C values . Preservation in 70% ethanol is typical for seabirds, but this may significantly increase the δ 13 C values ( ca 0.6‰), thereby affecting the Δ 13 C values. Alternatively, other storage methods, such as tubes coated in EDTA used in this study, appear to have a negligible effect on δ 13 C values of CC and plasma but may have some limited effects on plasma δ 15 N values (without EDTA: 16.5 ± 2.05‰; with EDTA: 15.6 ± 1.76‰).…”

“…As penguins are commonly held in zoological institutions, researchers have conducted controlled feeding experiments on gentoo ( Pygoscelis papua ), king ( Aptenodytes patagonicus ), rockhopper ( Eudyptes sp ), and Magellanic ( Spheniscus magellanicus ) penguins, resulting in three of six clades of the family having calculated DTDFs. All three previous studies published DTDF values for whole blood, but only one separated the blood components into the cellular component (CC) and plasma to calculate tissue‐specific DTDFs for Magellanic penguins .…”

“…), African ( Spheniscus demersus ), and Magellanic ( Spheniscus magellanicus ) penguins, resulting in three of six clades of the family having calculated DTDFs. All three previous studies published DTDF values for whole blood, but only one separated the blood components into the cellular component (CC) and plasma to calculate tissue‐specific DTDFs for Magellanic penguins . Indeed, this study is currently one of few measurements of plasma‐specific DTDF values published in the seabird literature …”

“…In contrast, the larger Magellanic penguin (3.2–4.7 kg) breeds in Chile and Argentina and includes more fish in its diet, typically the Argentine anchovy ( Engraulis anchoita ). Both species had DTDFs for whole blood published from controlled feeding studies, where Magellanic penguins were fed a diet of solely Argentine anchovy, while rockhopper penguins ( Eudyptes spp.) were fed a diet of capelin ( Mallotus villosus ).…”