Dental microwear texture analysis of extant koalas: clarifying causal agents of microwear
Hedberg, C & DeSantis, LRG 2016, Journal of Zoology, vol. 301, no. 1, pp. 206-214.
The dental microwear of the koala is consistent with that of other tough object feeders and reflects its dietary composition and behaviours. The most likely factors influencing microwear patterns in the koala are the properties of food consumed, abrasion during mastication and the ingestion of grit.
Dental microwear texture analysis (DMTA) can be used to interpret the dietary habits of vertebrates in the final stages of their lives. Conclusions drawn from DTMA are based on the assumption that consuming different foods will cause different microwear patterns. In particular, the presence or absence of phytoliths, microscopic silica particles found in varying quantities in plant matter, is thought to result in microwear patterns that reveal an animal’s dietary composition. This assumption has been questioned by those suggesting that microwear patterns result from the ‘grit’ that is ingested with food rather than the properties of the food itself. The purpose of this investigation was to determine whether factors other than phytoliths result in microwear that can be used to characterise the diets of herbivores. For this purpose, the koala is an ideal subject as its unique diet of Eucalyptus leaves lacks phytoliths but is likely to result in distinctive microwear patterns. Koalas were found have very high anisotropy values, which means they had multiple dental scratches of the same orientation. This high anisotropy is consistent with the consumption of tough plant matter such as leaves and grass. Koalas had high microwear complexity, suggesting the occasional consumption of hard items. Unlike other hard object feeders, however, koala teeth had relatively shallow microwear features. During September, the driest month of the year, koalas were observed to have low microwear complexity and shallow microwear features.
Several factors may contribute to the microwear patterns observed in koalas in the absence of dietary phytoliths. High microwear complexity values or dental ‘pitting’ may be explained by the occasional consumption of buds and stems while browsing leaves. Conversely, low microwear complexity and textural fill volume values are likely lowest in the dry period of September as koalas may demonstrate a preference for softer leaves with higher water content in arid conditions. Koalas are also highly likely to abrade the teeth during mastication. The koala has a powerful, side-to-side chewing style that causes the teeth to strike each other laterally. This repeated and concentrated pressure would likely result in high anisotropy values. Finally, it is likely that grit ingested with leaves contributes to microwear in the koala. Quartz particles present in dust throughout Queensland and New South Wales are capable of abrading enamel, contributing to the high anisotropy and complexity values observed here.
These findings indicate that dental microwear as a result of factors other than phytoliths can reveal aspects of an animal’s diet. Further, it is confirmed that the koala exhibits microwear patterns indicative of its diet and that DMTA can be employed to interpret these. The authors recommend further research into the potential for particles in soil, gravel and dust to abrade tooth enamel in herbivores.
Summarised by Joanna Horsfall
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