Stable nitrogen and carbon isotope discrimination between juveniles and adults in an income-breeding small mammal (Peromyscus maniculatus)

We investigated the stable nitrogen- and carbon-isotope compositions of blood, liver, muscle and hair of income breeding deer mice (Peromyscus maniculatus) to determine the extent to which stable isotope compositions of mothers and offspring differed. We found small differences between the δ15N and δ13C values of dependent offspring and adult tissues (by a magnitude of −0.8‰ to 1.1‰ for 15N and 0.3-0.9‰ for 13C), and limited 15N discrimination between juvenile tissues and milk, which explains the small mother-offspring trophic effects in isotopic composition. Discrimination of 15N between offspring and adults was greater than expected but smaller than known for capital breeding mammals, suggesting that different biochemical pathways for milk production and processing may affect the discrimination of 15N in these systems.