Changes to vertebrate tissue stable isotope (δ¹⁵N) composition during decomposition

Decomposition processes alter the chemical composition of organic matter, including isotopic signatures. While it is known that decomposition fluids differ from original tissue isotopes, the timeline and mechanisms of these changes remain unclear. Prior studies have shown that decomposition fluids are enriched in δ15N compared to intact tissues, but the extent and timing of this enrichment in tissues themselves are not well established. This uncertainty limits the use of carcass isotopes in ecological studies. The role of microbial activity and environmental factors in isotopic shifts is partially understood, but gaps remain in how these processes interact with tissue degradation. The disconnect between initial tissue composition and final fluid composition raises questions about the reliability of isotopic data from decomposing remains. Understanding these changes is critical for interpreting ecological data from field-collected carcasses. This study addresses the lack of detailed temporal data on tissue isotopic enrichment during decomposition. By examining δ15N changes in tissues at multiple decay stages, the research aims to clarify the dynamics of postmortem isotopic shifts.

The study aimed to investigate how δ15N values in vertebrate tissues change during decomposition. The researchers hypothesized that tissues would become progressively enriched in δ15N as decay progresses. This hypothesis is based on the known enrichment of decomposition fluids compared to fresh tissues. The study sought to determine the timing and rate of isotopic enrichment in tissues. Understanding these changes is essential for interpreting ecological data from decomposing carcasses. The research also aimed to identify the mechanisms behind isotopic shifts during decay. By collecting tissues at multiple time points, the study provides a detailed timeline of isotopic changes. This information will help ecologists assess the reliability of isotopic data from field-collected remains.

The researchers collected soft tissues and bone from beaver carcasses at five decomposition time points. Tissue samples included muscle and other soft tissues. Isotopic analysis focused on δ15N values to track changes over time. The study compared isotopic values from fresh tissues to those collected during decomposition. Researchers monitored decomposition stages to correlate isotopic shifts with decay processes. Tissue breakdown was observed through autolysis and microbial infiltration. The study also tracked the release of decomposition fluids and their isotopic composition. By analyzing δ15N enrichment in tissues and fluids, the researchers tested their hypothesis about progressive isotopic changes.

Soft tissues, including muscle, showed significant δ15N enrichment compared to fresh tissues. However, these tissues were not as enriched as decomposition fluids. The study found that δ15N enrichment increased progressively during decomposition. Tissue breakdown was initially dominated by anaerobic autolysis. Later stages involved microbial and insect infiltration, which may contribute to isotopic shifts. The researchers observed that δ15N enrichment in tissues was less than in fluids. They speculate that volatilization of δ15N-depleted compounds, like ammonia, may enhance fluid enrichment. These findings suggest that isotopic enrichment in tissues occurs but at a lower rate than in decomposition fluids.

The study found that soft tissues become progressively δ15N-enriched during decomposition. However, this enrichment is less pronounced than in decomposition fluids. The researchers propose that microbial activity and volatilization of δ15N-depleted compounds contribute to isotopic shifts. These results suggest that carcass isotopic data may not accurately reflect pre-mortem trophic positions. The study highlights the need for caution when using decomposing carcasses in ecological research. The timing and mechanisms of isotopic enrichment provide insights into decomposition processes. The findings indicate that decomposition fluids are more enriched than tissues. These results support the hypothesis that δ15N enrichment occurs during decay but at varying rates.