Tracing food webs with stable hydrogen isotopes

Area of Science:

• Stable isotope ecology
• Biogeochemistry
• Animal physiology

Background:

• Understanding the factors that influence an animal's isotopic composition is crucial for ecological and physiological studies.
• The relative contribution of food versus water to an animal's hydrogen isotopic content has been a subject of investigation.

Purpose of the Study:

• To determine whether food or water is the primary source of hydrogen isotopes in animal tissues.
• To investigate the relationship between dietary hydrogen isotopic content and the isotopic signature of animal tissues in controlled and natural settings.

Main Methods:

• Controlled feeding experiments with mice using diets with a constant deuterium to hydrogen ratio (D/H).
• Analysis of liver and muscle tissue from mice to determine their D/H ratios.
• Field study of Littorina obtusata snails and their algal diets in the northern Atlantic intertidal zone.
• Comparison of the D/H ratios in snails, their primary food source (Fucus vesiculosus), and other available algae.

Main Results:

• Mice tissues (liver and muscle) exhibited an average D/H ratio identical to their food source when diet and water D/H were kept constant.
• Littorina obtusata snails showed a D/H ratio that matched that of Fucus vesiculosus, their exclusive food source.
• The D/H ratio of snails did not reflect other available algal diets, highlighting dietary specificity.

Conclusions:

• An animal's hydrogen isotopic content is primarily determined by the isotopic content of its food, not its water.
• This principle holds true in both controlled laboratory settings (mice) and natural ecosystems (snails).
• Dietary hydrogen isotope analysis can be a reliable tool for tracing animal diets and understanding food web dynamics.