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Sex, Size and Gender RolesEvolutionary Studies of Sexual Size Dimorphism$
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Daphne J. Fairbairn, Wolf U. Blanckenhorn, and Tamás Székely

Print publication date: 2007

Print ISBN-13: 9780199208784

Published to Oxford Scholarship Online: September 2007

DOI: 10.1093/acprof:oso/9780199208784.001.0001

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

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

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(p.195) Chapter 19 Development of sexual size dimorphism in lizards: testosterone as a bipotential growth regulator
Source:
Sex, Size and Gender Roles
Author(s):

Henry B. John-Alder

Robert M. Cox

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199208784.003.0022

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.

Keywords:   growth rate, Iguania, lizard, phenotypic plasticity, Phrynosomatidae, Sceloporus, somatotrophic axis

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