Nitrogen stable isotope turnover and discrimination in lizards

Area of Science:

• Ecology
• Physiology
• Biogeochemistry

Background:

• Nitrogen stable isotope ratio (δ¹⁵ N) processes are poorly understood in reptiles, limiting trophic and nutrient dynamic inferences.
• Accurate δ¹⁵ N data is crucial for understanding reptilian foraging ecology and nutrient physiology.

Purpose of the Study:

• To detail nitrogen stable isotope (δ¹⁵ N) turnover and discrimination (Δ¹⁵ N) in diverse lizard tissues.
• To compare δ¹⁵ N dynamics with existing carbon isotope (δ¹³ C) data for improved ecological interpretations.

Main Methods:

• Quantified ¹⁵ N incorporation and discrimination over 360 days in blood, skin, muscle, and liver of two lizard species.
• Analyzed tissue samples using continuous flow isotope ratio mass spectrometry.

Main Results:

• Plasma and red blood cell (RBC) Δ¹⁵ N ranged from +2.7 to +3.5‰, with turnover rates varying significantly (20.7–303 days).
• Skin, muscle, and liver tissues did not equilibrate, hindering their use for isotope-based estimates.
• ¹⁵ N and ¹³ C incorporation patterns were uncoupled, particularly during winter hibernation.

Conclusions:

• Provides essential ¹⁵ N turnover rates and discrimination values for reptile isotope studies.
• Highlights the unreliability of somatic tissues for δ¹⁵ N analysis in reptiles.
• Suggests metabolic shifts during hibernation can decouple ¹⁵ N and ¹³ C dynamics.