Functionality of cheek teeth is essential for ruminants to masticate plant materials thoroughly and promote microbial degradation in their rumens. Thus, an excessive rate of tooth wear is expected to lead to premature loss of tooth functionality, and hence to reduced longevity. So far, however, the relationships between food habits, molar wear and longevity have not been investigated. We first compared molar wear rates among nine sika deer Cervus nippon populations with different food habits. We then investigated correlations between molar wear rate and two ecological factors, percentage of graminoids in diet and annual precipitation, relating to intrinsic and extrinsic abrasiveness of the ingested food, respectively. Secondly, we estimated 'retained molar durability' (molar height at a given age divided by wear rate) at successive ages for each population, and tested for correlation between molar durability and life expectancy among populations. The M 1 and M 3 wear rates differed among the populations and showed a positive correlation with graminoid consumption and a negative correlation with precipitation, suggesting that both ecological factors influence molar wear rates in the Japanese sika deer. M 3 durability had a stronger correlation with life expectancy than M 1 durability, especially at the older age stages. This implies that the influence of M 3 durability on life expectancy becomes stronger at the time when the M 1 is severely worn and loses its functionality, and is therefore more important for life span elongation than the M 1 . These results are concordant with the fact that the M 3 is the most hypsodont molar in many ungulates. In the Japanese sika deer, microevolutionary acquisition of hypsodonty appears to be the case in a northern population (the Kinkazan Island), whose molar wear rates are extremely rapid due to their food habits.

Morphological comparisons of the sika deer Cervus nippon mandible and molars were conducted between two (northern and southern) Japanese subspecific lineages and among local populations of different ('grazer' or 'intermediate feeder') feeding types. The northern lineage showed greater M 1 breadth, M 3 hypsodonty and mandibular corpus height than the southern lineage. Such differences were not observed between the 'grazer' and 'intermediate feeder' populations of the northern lineage. However, a northern population, which inhabits a particularly harsh environment (Kinkazan Island), had the largest values of relative molar size and hypsodonty, although this was not statistically significant. These results imply that, in the Japanese sika deer, the selective pressures acting on the current 'grazer' populations are not strong enough to bring out noticeable adaptive change in molar size and hypsodonty, but adaptive change in these traits may occur in an environment that promotes excessive molar wear, more than that seen in the current sika deer habitats of Japan. Combined with what is known of the Pleistocene history of the sika deer, we infer that the ancestral population of the northern Japanese lineage likely acquired their relatively larger and more hypsodont molars in an extremely harsh environment during the last or previous glacial periods.

Incisor size is associated with feeding efficiency in herbivorous ungulates and may have been under selection in correspondence with food habits. In the meantime, males of polygynous, dimorphic species have smaller cheek teeth than females, possibly because their reproductive span is much shorter than that of females. Thus, males are not under selection for more durable teeth when there is no reproductive return. Therefore, incisor size is expected to be under natural selection against wear and under the influence of sex‐based differences in reproductive strategy. We first investigated incisor wear in Japanese sika deer (Cervus nippon) and compared wear rates between the sexes and two ecologically contrasting populations on Kinkazan Island and Mt. Goyo. We then compared unworn incisor size to test the hypotheses that female deer have relatively larger incisors than males and a population with faster incisor wear has larger incisors. The Kinkazan deer showed significantly faster wear than those on Mt. Goyo, and Kinkazan males had faster wear than Kinkazan females. Unworn incisor size was relatively larger for females than that for males and was larger for Kinkazan deer than that for Mt. Goyo deer. The sex‐based difference in incisor size was greater in Mt. Goyo deer than that in Kinkazan deer. These findings support the hypothesis that sex‐based differences in reproductive span result in larger incisor size for female sika deer and imply that strong natural selection against rapid tooth wear diminishes sex‐based differences in incisor size in Kinkazan deer. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110, 384–397.

Haemaphysalis longicornis (Acari: Ixodidae) is one of the most common and important arthropod disease vectors in Japan, carrying Japanese spotted fever and bovine theileriosis. The recent expansion of sika deer (Cervus nippon, Artiodactyla: Cervidae) populations, the most common wild host of H. longicornis, has also caused concern about increasing the risk of vector-borne diseases in Japan. We used generalized linear mixed model analysis to determine the relative contribution of deer density and other biological and abiotic factors on the abundance of H. longicornis ticks questing at each developmental stage. A total of 6223 H. longicornis adults, nymphs, and larvae were collected from 70 sites in three regions of central Japan. The abundance of questing adult and nymphal ticks was associated with deer density and other biotic and abiotic factors. However, the abundance of questing larvae showed no association with deer density but did show an association with other biotic and abiotic factors. These findings show that a high density of deer along with other biotic and abiotic factors is associated with increased risk of vector-borne diseases through amplified local abundance of questing nymphal and adult H. longicornis. Further, questing larvae abundance is likely regulated by environmental conditions and is likely correlated with survival potential or the distribution of other host species.