Plasticity in sexual size dimorphism and Rensch’s rule in Mediterranean blennies (Blenniidae)

Comparative analyses of sexual size dimorphism (SSD) across species have led to the discovery of Rensch’s rule. This rule states that SSD increases with body size when males are the largest sex, but decreases with increasing size when females are larger. Within-species comparisons of SSD in fish are rare, yet these may be a valuable tool to investigate evolutionary patterns on a fine scale. This study compares SSD among closely related populations of three species of Mediterranean blennies (Blenniidae): Microlipophrys canevae (Vinciguerra, 1880), Parablennius incognitus (Bath 1968), and Aidablennius sphynx (Valenciennes, 1836). SSD varied more among populations than among species and Rensch’s rule was confirmed within two species. It is not likely that the variation among populations in SSD mirrors genetic variation, as many of the populations were in close proximity of one another, with a high potential for genetic exchange. This study complements larger scale analyses of other taxa and demonstrates the fine scale on which evolutionary processes responsible for Rensch’s rule may be operating.

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Bigger Males, Bigger Females? Pigeons’ Sexual Size Dimorphism

Annual Research & Review in Biology ◽

10.9734/arrb/2020/v35i1030286 ◽

2020 ◽

pp. 20-24

Author(s):

P. M. Parés- Casanova ◽

A. Kabir

Keyword(s):

Body Weight ◽

Body Size ◽

Sexual Size Dimorphism ◽

Wing Length ◽

Rensch’S Rule ◽

Size Dimorphism ◽

Rensch's Rule ◽

Neck Thickness ◽

Males And Females ◽

Domestic Pigeons

Sexual dimorphism, defined as phenotypic differences between males and females, is a common phenomenon in animals. In this line, Rensch’s rule states that sexual size dimorphism increases with increasing body size when the male is the larger sex and decreases with increasing average body size when the female is the larger sex. Domesticated animals offer excellent opportunities for testing predictions of functional explanations of Rensch’s theory. Pigeon breeds encounters many different functional purposes and selective constraints, which could influence strongly their morphology. The aim of this paper is to examine, for first time, Rensch’s rule among domestic pigeons. It was compiled a database of 12 quantitative traits (body weight, body height, beak thickness, beak length, neck length, neck thickness, wing length, rump width, tail length, tarsus length, tarsus thickness and middle toe length) for males and females of 11 different domestic pigeon breeds: Bangladesh Indigenous, Racing Homer, Turkish Tumbler, Indian Lotan, Kokah, Mookee, Indian Fantail, Bokhara Trumpeter, Bombai, Lahore and Hungarian Giant House; Rock Pigeon (Columba livia) was also considered as wild relative for comparative purposes. Comparative results between males and females showed that only body weight, wing length and neck thickness were consistent with Rensch’s rule. The rest of trait did not present correlations. Among domestic pigeons, there can appear different expressions of dimorphism according to each trait, so it must be considered that Rensch’s rule vary when considering other traits than body weight.

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

Proceedings of The Royal Society B Biological Sciences ◽

10.1098/rspb.2007.1043 ◽

2007 ◽

Vol 274 (1628) ◽

pp. 2971-2979 ◽

Cited By ~ 103

Author(s):

James Dale ◽

Peter O Dunn ◽

Jordi Figuerola ◽

Terje Lislevand ◽

Tamás Székely ◽

...

Keyword(s):

Sexual Selection ◽

Sexual Size Dimorphism ◽

Bird Species ◽

Confounding Factors ◽

Allometric Relationship ◽

Rensch’S Rule ◽

Size Dimorphism ◽

Rensch's Rule ◽

Clear Solution ◽

General Explanation

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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