Contribution of diet to [delta]¹⁵N, [delta]¹³C, and [Delta]¹⁴C values in the Pacific rat (Rattus exulans).
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis is the outcome of a research project undertaken to determine how diet can affect the reliability of rat bone (especially that of Rattus exulans) for accurate radiocarbon analysis. It addresses questions about the reliability of R. exulans bone for radiocarbon dating with respect to the survival of bone in archaeological and natural burial sites, laboratory processing methods, and the extent to which diet influences radiocarbon ages of bone. I have shown that R. exulans bone can return reliable radiocarbon dates, based on bone survival and the efficacy of chemical treatment to remove burial contamination. In three dietary investigations, stable isotope (13C and 15N) and radiocarbon (14C) analyses of modem populations and archaeological specimens also indicated that Rattus exulans and other omnivorous species can have radiocarbon values influenced by a diet linked to 14C – depleted reservoirs. Moreover, depleted carbon reservoir effects are localised and variable in their magnitude. Work on modem populations also provided an improved means of isotopic analysis in an ecological study, where bomb-generated radiocarbon (∆14C) signatures in the natural environment were used as for other "tracer" studies, in conjunction with stable isotopes (13C and 15N). Results indicated that the changing atmospheric 14C signal fixed into the biota in a given year by photosynthesis is transferred from plants through trophic levels to end-members, including rats. The additional isotopic "clue" about diet given by radiocarbon analysis offered a better understanding of the variation in diets of R. exulans in different habitats. Variation in the isotopic signal among individuals supported other observations that diets of scavenging rats are opportunistic and associated with faunal availability in different habitats. To better understand diet-induced radiocarbon variations, I also examined the carbon contribution to bone protein from essential amino acids in the diet. Essential amino acids are the biochemical "messengers" in the carbon transfer from diet to bone protein. I originally proposed that the dietary 14C contribution might be measured by HPLC separation of essential amino acids in bone protein. Analysis of a selection of amino acid separations from protein hydrolysates showed that essential and non-essential amino acids produced widely varying 13C and ∆14C. I hypothesise that the radiocarbon variations in non-essential amino acids may be due to metabolic effects that utilise essential amino acid carbon skeletons in the creation of non-essential amino acids.