INCISOR ARCADES OF ALASKAN MOOSE: IS DIMORPHISM RELATED TO SEXUAL SEGREGATION?

Abstract

We tested whether incisor arcades of Alaskan moose (Alces alces gigas) differed between males and females of known age to examine how allometric differences in jaw architecture might relate to sexual segregation. Lower jaws were collected from moose killed by hunters, and from moose that died of either natural causes of collisions with vehicles. We measured the breadth (width) and the depth (protrusion) of the incisor arcade of moose; age was determined by counting cementum annuli of incisors. Arcade breadth of moose followed von Bertalanffy models of growth, with an asymptote at about 4 years of age for both sexes. Regression models differed for males and female moose; arcade breath for males was significantly larger than for females. Data from the literature indicated body mass of females also reaches an asymptote at 4 years old. Males, however, do not attain an asymptote in body mass until 8-10 years of age. When incisor breadth was considered relative asymptotic body mass, incisor breadth of males was less than that of females. Coefficients of incisor breadth relative to body mass, however, scaled similarly for male (0.249) and female (0.260) moose. Incisor depth did not differ between the sexes when depth was corrected for age. Our data indicate that incisor breadth, but not depth, scaled with body mass. Thus, muzzle morphology may exhibit more plasticity than previously thought. We hypothesize that muzzle architecture of moose, as reflected in incisor breadth and depth, relates to the diets of the sexes when they are spatially segregated. Whether incisor dimensions are a cause or consequence of sexual segregation, however, is uncertain.