Development of sexual size dimorphism in lizards: Testosterone as a bipotential growth regulator

Henry B. John-Alder, Robert M. Cox

Research output: Chapter in Book/Report/Conference proceedingChapter

24 Scopus citations


Sexual size dimorphism (SSD) is widespread in lizards but little is known about why males are larger than females in most species, while the opposite is true in many others. This chapter presents case studies of the development of SSD in three species of Sceloporus (Iguania: Phrynosomatidae), representing both male-larger and female-larger SSD. In all three species, SSD derives from sex differences in growth rate, and common garden experiments reveal significant phenotypic plasticity for SSD mediated by greater environmental sensitivity of growth in males. Studies focusing on growth regulation in males reveal that testosterone has opposing effects in closely related species with opposite patterns of SSD. Thus, testosterone serves as a bipotential mediator of sex differences in growth rate. The chapter closes by discussing mechanisms through which testosterone can both stimulate and inhibit male growth, including direct effects on the somatotrophic axis and indirect effects involving energy acquisition and allocation.

Original languageEnglish (US)
Title of host publicationSex, Size and Gender Roles
Subtitle of host publicationEvolutionary Studies of Sexual Size Dimorphism
PublisherOxford University Press
ISBN (Electronic)9780191709036
ISBN (Print)9780199208784
StatePublished - Sep 1 2007

All Science Journal Classification (ASJC) codes

  • Agricultural and Biological Sciences(all)


  • Growth rate
  • Iguania
  • Lizard
  • Phenotypic plasticity
  • Phrynosomatidae
  • Sceloporus
  • Somatotrophic axis


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