Allometry of sexual size dimorphism in domestic dog.

Daniel Frynta,Petra Hradcová,Lukáš Kratochvíl,Jana Baudyšová,Kateřina Faltusová

doi:10.1371/journal.pone.0046125

Abstract

BackgroundThe tendency for male-larger sexual size dimorphism (SSD) to scale with body size – a pattern termed Rensch's rule – has been empirically supported in many animal lineages. Nevertheless, its theoretical elucidation is a subject of debate. Here, we exploited the extreme morphological variability of domestic dog (Canis familiaris) to gain insights into evolutionary causes of this rule.Methodology/Principal FindingsWe studied SSD and its allometry among 74 breeds ranging in height from less than 19 cm in Chihuahua to about 84 cm in Irish wolfhound. In total, the dataset included 6,221 individuals. We demonstrate that most dog breeds are male-larger, and SSD in large breeds is comparable to SSD of their wolf ancestor. Among breeds, SSD becomes smaller with decreasing body size. The smallest breeds are nearly monomorphic.Conclusions/SignificanceSSD among dog breeds follows the pattern consistent with Rensch's rule. The variability of body size and corresponding changes in SSD among breeds of a domestic animal shaped by artificial selection can help to better understand processes leading to emergence of Rensch's rule.

Highlights

Animal species that have undergone domestication processes usually exhibit rapid phenotypic change [1,2,3,4]
The extraordinary ability of domestic species to radiate into numerous morphologically and behaviorally distinct breeds within a few generations is explained by episodes of strong artificial selection [1,5]
We focus on allometry in sexual size dimorphism (SSD)

Summary

Introduction

Animal species that have undergone domestication processes usually exhibit rapid phenotypic change [1,2,3,4]. Differences in size are especially apparent among dog breeds, ranging from about two kilograms in the miniature Chihuahua to about 100 kilograms in the giant mastiff. This range encompasses the range of body mass reported for all other canids: from 1.3 kilograms in the fennec fox (Fennecus zerda) to 36.3 kilograms in the wolf [8]. Size differences, including those concerning differences between males and females, i.e., sexual size dimorphism (SSD), have many direct and indirect consequences [9,10]. We exploited the extreme morphological variability of domestic dog (Canis familiaris) to gain insights into evolutionary causes of this rule

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