Allometry of Sexual Size Dimorphism in Domestic Dog

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.

Cats and dogs cross the line: domestic breeds follow Rensch’s rule, their wild relatives do not

“…Sutter et al (2008) studied 27 body measurements of 109 dog breeds and determined that male/female proportions were maintained in small and large breeds thus Rensch's rule cannot occur. However, Frynta et al (2012) using shoulder height of 74 breeds obtained a significant positive allometric relationship between male and female size consistent with Rensch's rule. The occurrence of Rensch's rule in domestic dogs was confirmed by us using body mass as well as height at withers and there is little doubt that the trend exists.…”

“…SSD of domesticated animals has received some attention (e. g. Lark et al, 2006;Sutter et al, 2008;Polák, Frynta, 2010;Remĕs, Székely, 2010;Frynta et al, 2012) because it is well known that the process of domestication is usually accompanied by a "domestication syndrome". One of the "symptoms" of this syndrome is a generalized decrease in body size.…”

A phylogenetic approach to the study of sexual size dimorphism in Felidae and an assessment of Rensch´s rule.

“…Nuestros resultados han mostrado claramente que la regla de Rensch no se aplica a los Félidos y que el SSD y la masa corporal muestran patrones de distribución filogenética absolutamente no coincidentes a pesar de ser una familia esencialmente poligínica. Los cánidos, monógamos, tampoco presentan un patron de escalamiento entre SSD y tamaño corporal consistente con la regla de Rensch a nivel interespecífico (Bidau y Martínez, datos no publicados) aunque las razas del perro doméstico parecen cumplirla según algunos estudios (Frynta et al 2012) pero no según otros (Sutter et al 2008). De todos modos, las razas caninas son producto de la selección artificial y por lo tanto estos resultados no son probablemente relevantes al problema de la regla de Rensch en la naturaleza.…”

Ontogeny of sexual size dimorphism and environmental quality in Guatemalan children

“…In the present study, SSD was calculated as the logarithm of the mean male to mean female height ratio, representing the differences between logarithms of the male and female height: (ln(M/F) 5 ln M 2 ln F). This is the most commonly used method to estimate SSD and is used with slight variations in all recent research with sexually dimorphic species of animals, for example fruit flies (Testa et al, 2013), frogs and toads (Liao et al, 2013), ground squirrels (Mat ejů and Kratochv ıl, 2013), dogs (Frynta et al, 2012), and non-human primates, extinct hominins, and living people (Plavcan, 2012).…”