Dietary and homeostatic controls of Zn isotopes in rats: a controlled feeding experiment and modeling approach

The stable isotope composition of zinc (δ66Zn), which is an essential trace metal for many biological processes in vertebrates, is increasingly used in ecological, archeological, and paleontological studies to assess diet and trophic level discrimination among vertebrates. However, the limited understanding of dietary controls and isotopic fractionation processes on Zn isotope variability in animal tissues and biofluids limits precise dietary reconstructions. The current study systematically investigates the dietary effects on Zn isotope composition in consumers using a combined controlled feeding experiment and box-modeling approach. For this purpose, 21 rats were fed one of seven distinct animal- and plant-based diets and a total of 148 samples including soft and hard tissue, biofluid, and excreta samples of these individuals were measured for δ66Zn. Relatively constant Zn isotope fractionation is observed across the different dietary groups for each tissue type, implying that diet is the main factor controlling consumer tissue δ66Zn values, independent of diet composition. Furthermore, a systematic δ66Zn diet-enamel fractionation is reported for the first time, enabling diet reconstruction based on δ66Zn values from tooth enamel. In addition, we investigated the dynamics of Zn isotope variability in the body using a box-modeling approach, providing a model of Zn isotope homeostasis and inferring residence times, while also further supporting the hypothesis that δ66Zn values of vertebrate tissues are primarily determined by that of the diet. Altogether this provides a solid foundation for refined (paleo)dietary reconstruction using Zn isotopes of vertebrate tissues.

Mandible microwear texture analysis of crickets raised on diets of different abrasiveness reveals universality of diet-induced wear

Animals have evolved diverse comminuting tools. While vertebrates possess mineralized teeth, insect mandibles often bear metal-inclusion-hardened serrated cusps. Microscopic dental enamel wear (microwear) is known to be caused by contact with ingesta. To test if insect mandible microwear is also diet-dependent, we kept newly moulted adult two-spotted crickets (Gryllus bimaculatus) for four weeks on alfalfa-based rodent pellets with and without added mineral abrasives (loess, quartz, volcanic ash). Six crickets per diet were examined after 1, 3, 7, 14, 21 and 28 days. All diets induced progressive mandible wear, affecting specific locations along the distal tooth cusps differently. The depth of furrows increased on most abrasive-containing diets until day 21, while wear mark complexity increased from day 1 to 3 and 14 to 21. After 28 days, these parameter values for large volcanic ash and large quartz diets significantly exceeded those for the control diet. These results are comparable to observations from guinea pig feeding experiments with the same diets. Cricket mandible wear was affected by all abrasives. Notably, large volcanic ash and large quartz induced the deepest, most complex lesions, akin to observations in guinea pigs. This suggests a universal wear process, supporting that microwear analyses are suitable for inferring invertebrate diets.

Multiproxy approach to reconstruct fossil primate feeding behavior: Case study for macaque from the Plio-Pleistocene site Guefaït-4.2 (eastern Morocco)

The genus Macaca belongs to Cercopithecidae (Old World monkeys), Cercopithecinae, Papionini. The presence of Macaca in North Africa is well known from the Late Miocene to the Late Pleistocene. However, the diet of fossil Macaca has been poorly described in the literature. In this study, we investigated the feeding habits of Macaca cf. sylvanus (n = 4) from the Plio-Pleistocene site Guefaït-4.2 in eastern Morocco through multiproxy analysis combining analyses of stable carbon and oxygen isotopes from tooth enamel, buccal microtexture, and low-magnification occlusal dental microwear. For both microwear analyses, we compared the macaques with a new reference collection of extant members of Cercopithecoidea. Our occlusal microwear results show for the fossil macaque a pattern similar to the extant Cercocebus atys and Lophocebus albigena, African forest-dwelling species that are characterized by a durophagous diet based mainly on hard fruit and seed intake. Buccal microtexture results also suggest the consumption of some grasses and the exploitation of more open habitats, similar to that observed in Theropithecus gelada. The δ13C of M. cf. sylvanus indicates a C3 based-diet without the presence of C4 plants typical of the savanna grassland in eastern Africa during this period. The high δ18O values of M. cf. sylvanus, compared with the contemporary ungulates recovered from Guefaït-4.2, could be associated with the consumption of a different resource by the primate such as leaves or fresh fruits from the upper part of trees. The complementarity of these methods allows for a dietary reconstruction covering a large part of the individual’s life.

Controlled feeding experiments with juvenile alligators reveal microscopic dental wear texture patterns associated with hard-object feeding

Dental wear analyses are classically applied to mammals because they have evolved heterodont dentitions for sophisticated mastication. Recently, several studies have shown a correlation between pre-assigned and analytically inferred diet preferences in extant reptiles through dental microwear texture analysis (DMTA), a method using quantitative assessment of microscopic wear marks to reconstruct the diet material properties. The first tentative applications of DMTA to extinct reptiles have followed. However, for large and small mammals, microwear analyses have undergone a long time of ground-truthing through direct feeding observations, stomach content analyses, and feeding experiments. Such data are currently lacking for reptiles, but are necessary to further extend DMTA, especially to Archosauria, as the application to dinosaurs could be of great interest to the scientific community. We herein present data from a pilot feeding experiment with five juvenile American alligators (Alligator mississippiensis). Each individual received a diet of assumed different hardness for ~4 months: crocodylian pellets (control), sardines, quails, rats, or crawfish. All individuals initially received the same pellet diet, and we found them to show similar dental microwear texture patterns before they were switched to their designated experimental diet. From the first feeding bout on, dental microwear textures differed across the diets. The crawfish-feeder showed consistently higher surface complexity, followed by the rat-feeder. Quail- and fish-feeding resulted in similar wear signatures, with low complexity. Fast tooth replacement and selective tooth use likely affected microwear formation, but we were able to detect a general hard (crawfish and rat) versus soft (quail and fish) DMTA signature. Such patterns can support the identification of hard-object feeding in the fossil record.