Geographic Variation of Absolute and Relative Lower Molar Sizes in the Japanese Macaque (Macaca fuscata: Primates, Mammalia).
We examined geographic variations of absolute and relative lower molar sizes (size proportions among M1, M2, and M3) in the Japanese macaque (Macaca fuscata) using skull specimens obtained from 13 locations. We compared the geographic patterns and climatic factors. The size of M1significantly and negatively correlated to the annual and coldest month mean temperatures and precipitation for both males and females. The M2/M1and M3/M1scores significantly and positively correlated to the annual and coldest month mean temperatures. The geographic pattern in the size of M1was consistent with Bergmann's rule; however, the sizes of M2and M3did not correlate with temperature, and were not consistent with the rule. The geographic pattern in relative molar sizes (M2/M1and M3/M1scores) indicated that populations living in colder climates possess a larger M1in relation to M2and M3. Therefore, the correlations of M1, M2/M1, and M3/M1scores to temperature involve an increase in the size of M1in a colder climate. In macaques, the functions of the different molars (M1, M2, and M3) do not differ (they all exhibit grinding function, unlike differentiation between carnassial and other molars in Carnivora), whereas the timing of molar eruption does. In other words, at young ages (1.5-3.5 years), M1erupts and is in occlusion, whereas M2and M3do not erupt and are not used for mastication. Therefore, the geographic pattern in the relative molar sizes may be attributed to increasing survivability in harsh winter climates by increasing occlusal surface in younger animals.
College of Liberal Arts and Sciences, Mie University, Kurima-Machiya-Cho, Tsu, Mie 514-8507, Japan.
Masakazu
M
Asahara
Waseda Institute for Advanced Study, Waseda University, Shinjuku-Ku, Tokyo 169-8050, Japan.
Yuichiro
Y
Nishioka
D063147:Animal Distribution / Q000502:physiology*; D000818:Animals; D005260:Female; D008251:Macaca / Q000033:anatomy & histology* / Q000502:physiology*; D008297:Male; D008963:Molar / Q000033:anatomy & histology*
climate; dental morphology; evolution; growth; inhibitory cascade