Patterns, causes and consequences of tooth wear in cervids
Appears in the following Collection
- Biologisk institutt 
AbstractForaging ecology and environmental conditions have represented important driving forces in the evolution of both dental morphology as well as the digestive system. Teeth are essential for digestive processes in ruminants, and their persistent function and durability are regarded to be of major importance to animal performance and life-history strategies. Despite their high degree of wear resistance, teeth wear as a result of extensive use over time and the abrasive properties of plant foods. This potentially reduces their functionality and may thus reduce forage utilization, energy gain and in turn affect the animal’s life-history. This has to a little extent been investigated in the wild.
In this thesis I aim to study some causes and consequences of tooth wear among northern cervids. I also intend to evaluate the importance of current ecological and prior evolutionary factors as predictors for spatial patterns in tooth wear and investment.
My approach in Paper I was to quantify changes in occlusal topography, both related to age and individual body mass, and to assess its consequences for mastication efficiency. Data from the world’s northernmost ungulate, the Svalbard reindeer Rangifer tarandus platyrhynchus Vrolik, was used to investigate these questions. Inhabiting the Arctic deserts of Svalbard, this subspecies experience extreme environmental conditions, potentially representing a stronger selection pressure on teeth than the conditions experienced by herbivores living at lower latitudes. The results showed that occlusal topography decreased steadily with age, indicating a parallel reduction in mastication efficiency. As wear increased, the proportion of small particles in the reticulo-rumen decreased, indicative of reduced digestion efficiency. Heavy animals up to approximately five years of age had more worn teeth than lighter animals of the same age. This suggests a trade-off between early growth and tooth wear.
In Paper II I do a closer investigation of consequences from age-related tooth wear on reticulo-rumen retention and dimension. In addition, I also wanted to evaluate whether tooth wear could be linked to a potential reduction in energy gain. Again using the Svalbard reindeer as study species, I found that the mass of reticulo-rumen content and tissue increased with age. The increase of reticulo-rumen tissue suggests that physiological alterations occur in response to decreased mastication efficiency. Increased mass of reticulo-rumen content was likely a combination of the tissue enlargement and the altered particle properties due to reduced mastication efficiency. The summed effect of both changes is a permanent increase in digestive capacity. Amount of back fat decreased with advancing age. This suggests that alterations in digestive processes were not sufficient to compensate for reduced mastication efficiency.
The two fenced French roe deer Capreolus capreolus L. populations in Chizé and Trois Fontaines experience contrasting habitat quality and differ in several life-history traits. I used tooth measurements from animals of known age to test whether habitat quality or life span was the more important factor to tooth wear rate and durability. There was no between-population difference in tooth wear rate, and thus no effect of habitat quality on tooth wear. But, animals from the area with longer lifespan expectancy possessed higher initial molars, as would be expected if teeth investment was mainly decided by life-history. This linkage between lifespan and teeth endurance is in correspondence with evolutionary predictions.
In Paper IV, I compared inter- and intraspecific rates of both incisor and molar wear in a large browser (moose Alces alces L., six populations) and a mixed-feeder (red deerCervus elaphus L., four populations) to assess the importance of evolutionary history vs. the variation in current environmental conditions to patterns of tooth wear. The data covered both a substantial variation in environmental conditions and the main distribution area of both species in Norway. Analyses revealed that the mixed-feeder wore both incisors and molars faster than the browser, but there was no close link between incisor and molar wear rates at the population level. Although within-species tooth wear rates differed between populations, the species-specific molar wear patterns were consistent. Effect of population density was only detectable for red deer males. The results support the view that evolutionary history is responsible for the main patterns of interspecific molar wear patterns. Still, variation in environmental conditions caused variation in wear patterns within species, but this variation was much more pronounced in the mixed-feeding red deer than in the browsing moose.
In this thesis, I have demonstrated that reduced occlusal topography have consequences for digestive processes in ruminants, and argue that these changes may be likely causes of senescence. I also show how different causes (environmental conditions, body growth patterns, feeding-types) may generate variation in tooth wear patterns within and between species. I recommend future investigations to further reveal the functional relevance of age-related tooth wear for digestive mechanisms in ruminants, and possibly to link variation in tooth wear among individuals explicitly to individual life-time fitness.
LIST OF INDIVIDUAL PAPERS
Paper I: Veiberg, V., Mysterud, A., Bjørkvoll, E., Langvatn, R., Loe., L.E., Irvine, J.R., Bonenfant, C., Couweleers, F. & Stenseth, N.C. 2007. Evidence for a trade-off in early growth and tooth wear in Svalbard reindeer. Journal of Animal Ecology 76 (6): (In press) Journal of Animal Ecology 76(6)
Paper II: Veiberg, V., Mysterud, A., Irvine, R.J., Sørmo, W. & Langvatn, R. Increased reticulo-rumen filling with advancing age in Svalbard reindeer: a consequence of increased retention due to worn teeth? (Submitted Journal of Zoology)
Paper III: Veiberg, V., Mysterud, A. Gaillard, J.-M., Delorme, D., Van Laere, G. & Klein, F. 2007. Bigger teeth for longer life? Longevity and molar height in two roe deer populations. Biology Letters 3(3): 268-270. Biology Letters 3(3): 268-270
Paper IV: Veiberg, V., Loe, L.E., Mysterud, A., Solberg, E.J., Langvatn, R. & Stenseth, N.C. 2007. The ecology and evolution of tooth wear in red deer and moose. Oikos (In press) Oikos 116 (11), 1805–1818