Tracking cats: problems with placing feline carnivores on δO, δD isoscapes

Abstract

Background: Several felids are endangered and threatened by the illegal wildlife trade. Establishing geographic origin of tissues of endangered species is thus crucial for wildlife crime investigations and effective conservation strategies. As shown in other species, stable isotope analysis of hydrogen and oxygen in hair (δD(h), δ(18)O(h)) can be used as a tool for provenance determination. However, reliably predicting the spatial distribution of δD(h) and δ(18)O(h) requires confirmation from animal tissues of known origin and a detailed understanding of the isotopic routing of dietary nutrients into felid hair.

Methodology/findings: We used coupled δD(h) and δ(18)O(h) measurements from the North American bobcat (Lynx rufus) and puma (Puma concolor) with precipitation-based assignment isoscapes to test the feasibility of isotopic geo-location of felidae. Hairs of felid and rabbit museum specimens from 75 sites across the United States and Canada were analyzed. Bobcat and puma lacked a significant correlation between H/O isotopes in hair and local waters, and also exhibited an isotopic decoupling of δ(18)O(h) and δD(h). Conversely, strong δD and δ(18)O coupling was found for key prey, eastern cottontail rabbit (Sylvilagus floridanus; hair) and white-tailed deer (Odocoileus virginianus; collagen, bone phosphate).

Conclusions/significance: Puma and bobcat hairs do not adhere to expected pattern of H and O isotopic variation predicted by precipitation isoscapes for North America. Thus, using bulk hair, felids cannot be placed on δ(18)O and δD isoscapes for use in forensic investigations. The effective application of isotopes to trace the provenance of feline carnivores is likely compromised by major controls of their diet, physiology and metabolism on hair δ(18)O and δD related to body water budgets. Controlled feeding experiments, combined with single amino acid isotope analysis of diets and hair, are needed to reveal mechanisms and physiological traits explaining why felid hair does not follow isotopic patterns demonstrated in many other taxa.

Figure 1. Map of sampling sites.

Sample locations for both felines bobcat (n = 45) and puma (n = 30) as well as their preferred prey species eastern cottontail rabbit (n = 13) and white-tailed deer* (n = 31), respectively, plotted on the δ¹⁸O precipitation map of North America** (*data from ; **from http://www.waterisotopes.org).

Figure 2. Hydrogen isotope values of keratin relative to river water.

Plot of δD of hair (δD_h) from bobcat, puma and eastern cottontail rabbit as well as bone collagen (δD_bc) from white-tailed deer* vs. mean annual δD of river water (δD_riv) (*data from [56]).

Figure 3. Oxygen isotope values of keratin relative to river water.

Plot of δ¹⁸O of hair (δ¹⁸O_h) from bobcat, puma and eastern cottontail rabbit and bone phosphate (δ¹⁸O_bp) from white-tailed deer* vs. mean annual δ¹⁸O of river water (δ¹⁸O_riv) (*data from [56]).

Figure 4. Hydrogen and oxygen isotope ratios of keratin.

Hydrogen and oxygen isotope compositions are shown for hair samples (δD_h, δ¹⁸O_h) from puma, bobcat and eastern cottontail rabbit as well as collagen (δD_bc) and bone phosphate (δ¹⁸O_bp) data from white-tailed deer* (*data from [56]).

Figure 5. Hydrogen isotope model of herbivores and carnivores.

Model of hydrogen isotope physiology and the contribution of food and water to non-exchangeable hydrogen in the hair of herbivores and carnivores. Letters represent processes where isotope fractionation occurs (see text for detailed discussion). Blue coloring represents water inputs and green food inputs.