Stable isotopes significantly advance diet characterization, but tracking individual changes over time remains challenging. Micro-dissection of eye lenses has emerged as a cost-efficient tool for reconstructing individual dietary shifts, as they act as inert records of carbon and nitrogen isotope ratios over growth. However, their potential and applicability in the wild remain elusive. In this study, we used eye lens isotopes in well-characterized ecosystems (lakes and rivers) in Greenland to reconstruct the individual dietary shifts of Arctic char. Our results align with population data, and bulk muscle tissue’s isotopic content closely resembles that of the outermost layer, supporting its interpretation. We applied this methodology in a lake with two recently evolved sister species of Arctic char, one planktivorous and one piscivorous. While the juvenile diet remains unknown due to capture difficulties, we found that juveniles of both species occupy a unique isotopic niche, partly overlapping (30-40%), and two trophic levels less than adult piscivores (Δδ¹⁵N ~ 8 ‰), surpassing previous assumptions. Using linear mixed models, we demonstrate that diet is influenced by individual history (i.e., previous diet) and genetic factors (species). Furthermore, our examination of the individual components reveals that dietary plasticity is subject to selection pressure, with the piscivorous species exhibiting less predictable trajectories. Our study illustrates the importance of integrating individual isotopes over time to understand ecological and evolutionary processes.

Authors:

Coralie Moccetti, Eawag  (coralie.delarue@eawag.ch)

Jakob Brodersen, Eawag  (jakob.brodersen@eawag.ch)

Carsten Schubert, Eawag  (carsten.schubert@eawag.ch)