Abstract

We examine how dental sexual dimorphism develops in mandrills, an extremely sexually dimorphic primate. We aimed to (a) establish the chronology of dental development (odontochronology) in male and female mandrills, (b) understand interindividual and intersex variation in odontochronologies, and (c) determine how dental sexual dimorphism is achieved. We prepared histological ground sections from the permanent teeth of four female and four male mandrills from the semi-free ranging colony at the Centre International de Recherches Médicales, Franceville, Gabon. We used the microscopic growth increments in the sections to create odontochronologies. We compared ages at crown initiation, crown formation times (CFT) and crown extension rates (CER) between individuals and sexes to assess interindividual and intersex variation. All mandrill teeth are sexually dimorphic in size. Dental sexual dimorphism in mandrills is achieved via sex differences in the duration of growth (bimaturism) and in growth rates. We also found interindividual and intersex variation in the ages at initiation and completion of crown formation. Our results show that the rate of ameloblast differentiation varies between individuals and that selection for both the age at tooth initiation and CER has occurred independently in males and females to ensure that the teeth develop at appropriate times relative to the growth of the sexually dimorphic jaws. They also show that canine dimorphism is achieved through differences in both CER and CFT, unlike extant great apes or Cantius. Given at least three mechanisms for achieving canine dimorphism, we need more information to trace the evolution of this trait in primates.

Highlights

  • Animals have finite resources to allocate to growth, maintenance and reproduction

  • We examine how sexual dimorphism develops in teeth in an extremely sexually dimorphic primate, the mandrill (Mandrillus sphinx), using dental histology to reconstruct dental development

  • Our results clearly show that all mandrill teeth are sexually dimorphic in size, as in other cercopithecoids (Swindler, 2002), as the enamel dentine junction (EDJ) is longer in males than in females in all teeth (Table 3), supporting our first hypothesis

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Summary

Introduction

Animals have finite resources to allocate to growth, maintenance and reproduction. Life history theory suggests that natural selection shapes the allocation of these resources to maximize fitness (Stearns, 1992). Developing sexually dimorphic characteristics is costly for the sex that does so—often the male among primates— and an understanding of how such characteristics develop can help us to understand the function and evolution of sexual dimorphism (Leigh, 1992, 1995; Pereira & Leigh, 2003; Setchell & Lee, 2004; Watts, 1985). We examine how sexual dimorphism develops in teeth in an extremely sexually dimorphic primate, the mandrill (Mandrillus sphinx), using dental histology to reconstruct dental development

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