Determining biological tissue turnover using stable isotopes: the reaction progress variable

Abstract

The reaction progress variable is applied to stable isotope turnover of biological tissues. This approach has the advantage of readily determining whether more than one isotope turnover pool is present; in addition, the normalization process inherent to the model means that multiple experiments can be considered together although the initial and final isotope compositions are different. Consideration of multiple isotope turnover pools allows calculation of diet histories of animals using a time sequence of isotope measurements along with isotope turnover pools. The delayed release of blood cells from bone marrow during a diet turnover experiment can be quantified using this approach. Turnover pools can also be corrected for increasing mass during an experiment, such as when the animals are actively growing. Previous growth models have been for exponential growth; the approach here can be used for several different growth models.

Hydrogen and oxygen isotope ratios in human hair are related to geography

“…We asked how well the model could be inverted to predict the isotope ratio of the tap water for the city in which the hair sample originated. For these 65 hair samples, we again achieved 85% and 86% agreement, respectively, between the predicted and observed ''isotopic origins'' of both the ␦ 2 H h and ␦ 18 Hair has been shown to be a sequential recorder of changes in diet (3,12,(32)(33)(34)(35). Similarly, geographic movements by an individual between locations with contrasting tap-water isotope ratios should be detectable.…”

“…If not, the geographical maps make explicit predictions of the regions in the United States that would be isotopically consistent with the observed hair isotope ratios for that individual. In addition, by using the range of known growth rates of human hair and models of tissue turnover (33), it may be possible to place constraints on the time when an individual moved from one locality to another. Although it is perhaps early to make explicit predictive use of Fig.…”

“…Changes in the ␦ 2 H h and ␦ 18 O h values were detected in the first hair interval produced after arriving in the new city. The exponential approach of the ␦ 2 H h and ␦ 18 O h values to the new location suggested a 95% turnover in ␦ 2 H h and ␦ 18 O h values of Ͻ3 months and transition rate is predictable by using a reaction progress model (33).…”

History of Animals using Isotope Records (HAIR): A 6-year dietary history of one family of African elephants

“…4). These temporal relationships are compared with the timing of reproduction in the greater Samburu population (22,29). Seasonal diet changes were abrupt at the beginning of the wet season but tapered off gradually at the end of the wet season (Fig.…”

“…This study builds on our long-term observations of elephants in northern Kenya (19)(20)(21)(22)(23)(24), on our interests in understanding isotope incorporation into animal tissues (12,(25)(26)(27)(28)(29)(30), and on our interests in applying those principles to wildlife ecology (14,15,16). Diet records are interpreted from multiple hair samples collected annually or subannually over the study interval.…”