Abstract:
Stable isotope analysis is frequently applied as a tool to examine dietary patterns in
animals. However, some of the underlying assumptions associated with using this
approach are increasingly being questioned. We carried out a controlled diet
experiment on the southern African spiny mouse (Acomys spinosissimus Peters,
1852) to test a number of aspects relating to these assumptions and also examine
the hypothesis that stable isotopes, especially δ15N, can be used to provide evidence
of nutritional stress. We compared the δ13C and δ15N values of livers and blood from
animals that were fed ad libitum with animals undergoing a 10% reduction in food
supply. Food-restricted animals showed no significant difference in δ15N; however,
δ13C values of both liver and blood were depleted. Restricted animals also had a
significantly lower C:N ratio. We examined the role of lipids and found following lipid
extraction that both livers and lipids still showed the same separation in carbon
values. Tissue–diet discrimination values were also calculated and found to be
higher for both Δ13C and Δ15N compared with other mice species. Empirical values
for discrimination rates were then compared with values calculated using an
alternative method based on employing generic values and were found to be
dissimilar, suggesting the use of generic values are not always appropriate. Our
results highlight the need for greater understanding of the assumptions associated
with using stable isotope analysis to examine diet and we suggest that studying a
single species under captive conditions presents an ideal method to begin to test
these hypotheses.
