Allometry for Sexual Size Dimorphism: Pattern and Process in the Coevolution of Body Size in Males and Females

Abstract

Sexual size dimorphism (SSD) is common in both plants and animals, and current evidence suggests that it reflects the adaptation of males and females to their different reproductive roles. When species are compared within a clade, SSD is frequently found to vary with body size. This allometry is detected as β ≠ 1, where β is the slope of a model II regression of log(male size) on log(female size). Most frequently, β exceeds 1, indicating that SSD increases with size where males are the larger sex, but decreases with size where females are larger, a trend formalized as “Rensch's rule.” Exceptions are uncommon and associated with female-biased SSD. These trends are derived from a sample of 40 independent clades of terrestrial animals, primarily vertebrates. Their extension to plants and aquatic animals awaits quantitative assessments of allometry for SSD within these groups. Many functional hypotheses have been proposed to explain the evolution of allometry for SSD, most featuring sexual selection on males or reproductive selection on females. Of these, the hypothesis that allometry evolves because of correlational selection between the sexes appears most promising as a general model but remains untested.

Life history as a constraint on plasticity: developmental timing is correlated with phenotypic variation in birds

“…If there is a constraint on body size within eggs, larger species may have more post-hatching growth, opening up more opportunity for environmental influences. This could explain why larger species showed greater phenotypic variation in this study (Tables 1 and 3) and recalls the positive correlation seen across species between body size and the degree of sexual size dimorphism (Fairbairn, 1997). This suggests a specific mechanism by which a change in life history (in association with body size) affects exposure to environmental variation and thus the expression of phenotypic plasticity.…”

Macroevolutionary patterns of sexual size dimorphism in copepods

“…The fact that relationships are commonly not distinguishable from being isometric in many copepod clades suggests that selection on each of the sexes may have been near equally important. Most previous empirical assessments of allometry have focused on either vertebrates or invertebrates with male-biased SSD ( [3,6,7], cf. 8]) and in many of these studies the allometric slope within clades often decreases as the magnitude of SSD increases (see fig.…”

“…Differences in body size, termed sexual size dimorphism (SSD), are commonly observed in the plant and animal kingdoms [2] and can be measured with a sexual dimorphic index (SDI). Female-biased SSD, where females are larger than the males, tends to predominate in ectothermic invertebrate and vertebrate species, whereas male-biased SSD is common in many birds and mammals [3,4]. Various rules and theories have been proposed to explain variation in SSD, both within and between species.…”

Ecología trófica, dimorfismo sexual y parámetros reproductivos en el lagarto endémico Andino Liolaemus vallecurensis, Argentina

“…Se ha discutido que la divergencia trófi ca entre sexos es una posible fuerza selectiva que conduce a la diferenciación morfológica reduciendo la competencia intraespecífi ca (Pianka, 1982;Fairbairn, 1997;Cox et al, 2007). Se han propuestos diferentes hipótesis para brindar una explicación a este fenómeno, siendo estás asociadas a una selección sexual, natural (interacciones ecológicas) y selección de fecundidad (Hedrick & Temeles, 1989;Fairbairn, 1997;Cox et al, 2007;Vincent & Herrel, 2007).…”

“…Se han propuestos diferentes hipótesis para brindar una explicación a este fenómeno, siendo estás asociadas a una selección sexual, natural (interacciones ecológicas) y selección de fecundidad (Hedrick & Temeles, 1989;Fairbairn, 1997;Cox et al, 2007;Vincent & Herrel, 2007). El principal inconveniente radica en que estos tres mecanismos conducen al mismo fenómeno y en ocasiones puede resultar problemático (Anderson & Vitt, 1990;Pincheira-Donoso, 2012).…”