Female sika deer have evolved larger incisors than males under relaxed selection against rapid tooth wear

Abstract

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.

Wear Fast, Die Young: More Worn Teeth and Shorter Lives in Iberian Compared to Scottish Red Deer

“…Our results also showed that the factor ‘location’ made the greatest contribution of the random effects on molar and incisor wear, indicating that conditions prevailing at each particular area (e.g. hunting estates) can play an important role in tooth wear, in agreement with previous interpopulation comparisons [ 18 , 37 , 38 ].…”

“…Kubo et al [ 38 ] studied two sika deer ( Cervus nippon ) populations and only found heavier incisor wear in males in comparison with females in the population with stronger wear. These results suggest that although sexual selection may ultimately be responsible for male and female differences in tooth wear, environmental conditions may act to modulate them as has been shown for many other sexually dimorphic traits (see Bondurianski [ 40 ] and references herein).…”

Temporal changes in molar wear rate of a sika deer population under density‐dependent food limitation

“…However, in the case of another sika deer population (Kinkazan Island population) under density‐dependent food limitation, Kubo et al . () found that tooth wear rate was significantly different between sexes. The presence or absence of sex differences in wear rate seems to be associated with the existence of sex differences in food habits.…”

“…In sexually dimorphic ruminants, energetic requirements and food selection are different between sexes (Mysterud, ), which in turn seems to be associated with faster molar wear rate in males than females (red deer: Loe et al ., ; Carranza et al ., ; but see Pérez‐Barbería et al ., for less a conspicuous sex difference in molar wear rate). Incisor wear of sika deer has shown similar patterns where males have faster wear rates than females in a population under density‐dependent resource limitation (Kubo et al ., ). It is interesting that, in both of molars and incisors, males of dimorphic species had relatively small teeth compared with females, though they had faster tooth wear rates (Carranza et al ., ; Carranza & Pérez‐Barbería, ; Kubo et al ., ).…”

“…Incisor wear of sika deer has shown similar patterns where males have faster wear rates than females in a population under density‐dependent resource limitation (Kubo et al ., ). It is interesting that, in both of molars and incisors, males of dimorphic species had relatively small teeth compared with females, though they had faster tooth wear rates (Carranza et al ., ; Carranza & Pérez‐Barbería, ; Kubo et al ., ). This difference in initial tooth size is thought to reflect differences in reproductive lifespan between the sexes.…”