Author contributions
MKK, MDE, and ELV conceived the study. MKK collected samples and conducted the stable isotope experiment with assistance from JTK, AH, TWB, and MDE. CCM and AAB conducted the laboratory experiment. PAE and JTK performed the genetic analyses. MKK and PAE analyzed the data. MKK wrote the paper with contributions from CCM, PAE, JTK, AH, TWB, ELV, and MDE.