The turnover of dental microwear texture: Testing the" last supper" effect in small mammals in a controlled feeding experiment

Dental microwear texture (DMT) analysis is commonly applied for dietary reconstruction of vertebrates. The temporal scale on which dietarily informative microscopic wear forms on enamel surfaces is crucial to infer dietary flexibility and seasonality. Microwear is assumed to form shortly before the individual's death, reflecting information pertaining to the last meals consumed (“last supper” effect). In primate feeding experiments, microwear features formed within hours, suggesting rates of turnover within one to two weeks. As DMT formation experiments testing the persistence of microwear three-dimensionally (textures) are still lacking, we test how quickly DMTs form and pre-existing ones are overwritten in a terminal feeding experiment with 72 rats. In two groups of 36, rats received either a standard pelleted diet or the same pelleted diet containing 4% loess, an aeolian, silt-sized sediment, for 24 consecutive days. Then 6 individuals from each group were sacrificed, while the rest (n = 30) were switched to the diet they had not received before. On day 1, 2, 4, 8, 16, and 24 after the diet switch, 5 of the remaining individuals were sacrificed, creating a cohort of n = 5 each for each time point. We applied DMT analysis on first and second upper molars. For upper second molars, rats show a subsequent change in DMT after the switch, with visible differences from day 2 on. On upper first molars, microwear textures were variable for individuals sacrificed directly after the initial 24-day feeding period, thus obscuring significant differences in diet-induced dental wear. We find turnover faster and more pronounced when switching from loess-containing to standard pellet as compared to the opposite switch. The trend for either decreasing or increasing parameter values after the diet switch approaches a plateau between 16 and 24 days for many DMT parameters, suggesting that, under these experimental conditions, the “last supper” effect needs at least two weeks to overwrite previous DMT patterns