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Abstract Sexual dimorphism describes phenotypic differences between the sexes; the most prominent of which is sexual size dimorphism (SSD). Rensch’s rule (RR) is an allometric trend in which SSD increases in male-larger taxa and decreases in female-larger ones. Covariation between a trait and overall size within and across species can both be affected by sexual and natural selection. Thus, intraspecific allometric variation could influence the expression of RR. Here we used computer simulations to dissect how RR emerges under specific allometric patterns of intraspecific sexual differentiation in a trait. We found that sexual differentiation in static allometric slopes is the main determinant of RR. Based on our findings, RR and its converse can manifest in both body size and other traits. As a realistic showcase, we also examined RR and static allometry of different body parts in Mediterranean green lizards to establish whether intraspecific and evolutionary allometry are linked. Here, we identified RR and its converse for different traits, where the amount of sexual differentiation in static allometric slopes within species had a significant contribution to RR. Integrating the simulations and the empirical case we corroborate that sexual differentiation in static allometric slopes is a major parameter affecting evolutionary allometry.
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Wings of fringed fruit-eating bats (Artibeus fimbriatus) are highly integrated biological airfoils from perspectives of secondary-sexual dimorphism, allometry and modularity
Phenotypic variability is ubiquitous. This is especially true in bats where families such as Phyllostomidae encompass as much phenotypic variability as some entire orders of mammals. Typically, phenotypic variability is characterized based on cranial morphology with studies of other functionally important aspects of the phenotype such as legs, feet and wings less frequent. We examined patterns of secondary-sexual dimorphism and allometry of wing elements of the fringed fruit-eating bat (Artibeus fimbriatus) as well as examined for the first time modularity of bat wings. Patterns were based on 13 wing measurements taken from 21 female and 15 males from eastern Paraguay. From a multivariate perspective A. fimbriatus exhibited significant secondary-sexual dimorphism. Females were larger than males for all 13 wing characteristics with significant differences involving the last phalanx of the 4th and 5th digits. Female wings were also relatively larger than male wings from a multivariate perspective as well as the last phalanx of the 4th and 5th digit, after adjusting for wing size based on forearm length. Wing elements were highly variable regarding allometric relationships with some exhibiting no allometric patterns, and others exhibiting isometry or hyperallometry depending on the element. Wings exhibited significant modularity with metacarpals, proximal phalanges and distal phalanges each representing a discrete module. Wings of A. fimbriatus exhibit substantive patterns of dimorphism, allometry and modularity. While the Big Mother Hypothesis is a strong theoretical construct to explain wing dimorphism, there is yet no sound theoretical basis to patterns of allometry and modularity of the wing. Indeed, trying to understand the determinants of variation in wing morphology is ripe for future investigation.
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- Award ID(s):
- 2101909
- PAR ID:
- 10470646
- Publisher / Repository:
- Linnean Society
- Date Published:
- Journal Name:
- Biological Journal of the Linnean Society
- ISSN:
- 0024-4066
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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