Variations in stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) in different body parts and eggs of adult stoneflies (Plecoptera)

Variations in delta C-13 and delta N-15 might arise from differences in nutrient allocation. Residence times of delta C-13 and delta N-15 vary among tissues depending on metabolic turnover rates. However, because of their small size, entire individual insects are generally used as single samples in isotope analyses. The present study aimed to determine the degree of isotope similarity among regions of the adult body and eggs in four species of Plecoptera (Amphinemura sp., Sweltsa sp., Kamimuria tibialis Pictet and Ostrovus sp.). Levels of delta C-13 and delta N-15 differ between the four species, being lowest in Amphinemura sp., and with delta N-15 being highest in Sweltsa sp. Egg masses contain consistently the lowest values of delta C-13 in the four species, with the delta N-15 value of eggs being highest in K. tibialis and Ostrovus sp., and lower in Amphinemura and Sweltsa spp. In Sweltsa sp., the delta N-15 levels of the dermal layers and cuticle are lowest, whereas the delta C-13 values of the dermal layers and cuticle are almost equal to those in other regions of the body, except egg masses. Oviposited individuals of Amphinemura and Sweltsa spp. have lower delta N-15 levels than individuals that have not oviposited. The rates of metabolism and incorporation of dietary metabolites will differ depending on the body regions and species. Differences in egg ecology such as egg developmental period and egg buoyancy among species are considered to impact on the values of delta C-13 and delta N-15. These results will be useful for understanding the nutritional status of aquatic insects and their energy allocation.