Sex Affects Age Determination and Wear of Molariform Teeth in White-Tailed Deer

Abstract

Field estimation of the ages of adult white-tailed deer (Odocoileus virginianus) and other ungulates often requires assessment of the degree to which molariform teeth wear over time. This widely used technlque is applied without regard to the sex of the animal being aged, but sex-based differences in ungulate life history traits such as diet, habitat use, and foraging behavior may affect tooth wear patterns differently for males and females. We examined sex-specific differences in tooth wear and morphology for adult (>1.5 yrs old) deer collected in northeastern Illinois (1993-97). We randomly sampled 100 mandibles from adult deer (50 M:50 F), stratified by cementum annuli year classes 2-7, to obtain 29 measurements of width, height, length, and visible dentine on premolars 2 and 4, and molars 1 and 3. Principle components (PC) analysis indicated that 61% of the overall sample variation was explained by PCs 1-3. Analysis using MANOVAs suggested effects (P < 0.05) due to sex and age when component scores from PCs 1-3 were used as dependent variables. Teeth from male deer were wider and tended to show more visible dentine (wear) on occlusal surfaces. Age class estimates of 10 experienced observers indicated substantial observer variation in the wear-replacement aging technique A repeated measures ANOVA indicated that sex effects in the wear-replacement aging technique become significant when the effects of observer variation are controlled. Stage-based projection models based on sex-specific age ratios of white-tailed deer had different growth rates and adult sex ratios when corrected for a sex bias in wear-replacement aging, indicating that common population analysis methods are sensitive to a sex-based bias. Managers should use caution when comparing adult age ratios derived from tooth wear because of potential sex biases in tooth wear patterns.