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Sexual selection explains Rensch's rule of allometry for sexual size dimorphism.

Dale J, Dunn PO, Figuerola J, Lislevand T, Székely T, Whittingham LA - Proc. Biol. Sci. (2007)

Bottom Line: However, despite numerous recent studies, we still do not have a general explanation for this allometry.This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism.Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size.

View Article: PubMed Central - PubMed

Affiliation: Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, PO Box 1564, 82305 Starnberg (Seewiesen), Germany. dale@orn.mpg.de

ABSTRACT
In 1950, Rensch first described that in groups of related species, sexual size dimorphism is more pronounced in larger species. This widespread and fundamental allometric relationship is now commonly referred to as 'Rensch's rule'. However, despite numerous recent studies, we still do not have a general explanation for this allometry. Here we report that patterns of allometry in over 5300 bird species demonstrate that Rensch's rule is driven by a correlated evolutionary change in females to directional sexual selection on males. First, in detailed multivariate analysis, the strength of sexual selection was, by far, the strongest predictor of allometry. This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism. Second, in groups where sexual selection is stronger in females, allometry consistently goes in the opposite direction to Rensch's rule. Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size.

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Phylogenetically independent contrasts analysis of allometry for sexual size dimorphism versus (a) degree of polygamy, y=0.071x, p<0.0001 (with outlier removed: y=0.073x, p<0.0001, R2=0.17) and (b) aerial display agility, y=0.014x, p=0.001. Contrasts in allometric slopes were calculated on log-transformed values.
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fig3: Phylogenetically independent contrasts analysis of allometry for sexual size dimorphism versus (a) degree of polygamy, y=0.071x, p<0.0001 (with outlier removed: y=0.073x, p<0.0001, R2=0.17) and (b) aerial display agility, y=0.014x, p=0.001. Contrasts in allometric slopes were calculated on log-transformed values.

Mentions: Interestingly, aerial display agility of males was also a significant predictor of allometry, where subfamilies with more elaborate male aerial displays demonstrated stronger positive allometry (partial R2=0.066; table 2b; also see figure 3b). This result provides additional support for the hypothesis that differential sexual selection on size between the sexes drives Rensch's rule. Recall that the sexual selection hypothesis predicts positive allometry when males are under stronger directional selection than females, regardless of whether the males are selected to be larger or smaller. Indeed, in species with elaborate male aerial display, sexual selection is generally argued to be stronger for smaller male size because it greatly improves aerodynamic efficiency (Andersson & Norberg 1981; Székely et al. 2004; Raihani et al. 2006).


Sexual selection explains Rensch's rule of allometry for sexual size dimorphism.

Dale J, Dunn PO, Figuerola J, Lislevand T, Székely T, Whittingham LA - Proc. Biol. Sci. (2007)

Phylogenetically independent contrasts analysis of allometry for sexual size dimorphism versus (a) degree of polygamy, y=0.071x, p<0.0001 (with outlier removed: y=0.073x, p<0.0001, R2=0.17) and (b) aerial display agility, y=0.014x, p=0.001. Contrasts in allometric slopes were calculated on log-transformed values.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2211517&req=5

fig3: Phylogenetically independent contrasts analysis of allometry for sexual size dimorphism versus (a) degree of polygamy, y=0.071x, p<0.0001 (with outlier removed: y=0.073x, p<0.0001, R2=0.17) and (b) aerial display agility, y=0.014x, p=0.001. Contrasts in allometric slopes were calculated on log-transformed values.
Mentions: Interestingly, aerial display agility of males was also a significant predictor of allometry, where subfamilies with more elaborate male aerial displays demonstrated stronger positive allometry (partial R2=0.066; table 2b; also see figure 3b). This result provides additional support for the hypothesis that differential sexual selection on size between the sexes drives Rensch's rule. Recall that the sexual selection hypothesis predicts positive allometry when males are under stronger directional selection than females, regardless of whether the males are selected to be larger or smaller. Indeed, in species with elaborate male aerial display, sexual selection is generally argued to be stronger for smaller male size because it greatly improves aerodynamic efficiency (Andersson & Norberg 1981; Székely et al. 2004; Raihani et al. 2006).

Bottom Line: However, despite numerous recent studies, we still do not have a general explanation for this allometry.This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism.Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size.

View Article: PubMed Central - PubMed

Affiliation: Department of Behavioural Ecology and Evolutionary Genetics, Max Planck Institute for Ornithology, PO Box 1564, 82305 Starnberg (Seewiesen), Germany. dale@orn.mpg.de

ABSTRACT
In 1950, Rensch first described that in groups of related species, sexual size dimorphism is more pronounced in larger species. This widespread and fundamental allometric relationship is now commonly referred to as 'Rensch's rule'. However, despite numerous recent studies, we still do not have a general explanation for this allometry. Here we report that patterns of allometry in over 5300 bird species demonstrate that Rensch's rule is driven by a correlated evolutionary change in females to directional sexual selection on males. First, in detailed multivariate analysis, the strength of sexual selection was, by far, the strongest predictor of allometry. This was found to be the case even after controlling for numerous potential confounding factors, such as overall size, degree of ornamentation, phylogenetic history and the range and degree of size dimorphism. Second, in groups where sexual selection is stronger in females, allometry consistently goes in the opposite direction to Rensch's rule. Taken together, these results provide the first clear solution to the long-standing evolutionary problem of allometry for sexual size dimorphism: sexual selection causes size dimorphism to correlate with species size.

Show MeSH