Sexual dimorphism in human cranial trait scores: Effects of population, age, and body size

It is well recognized that differences in environmental selection pressures among populations can generate phenotypic divergence in a suite of morphological characteristics and associated life history traits. Previous analysis of mitochondrial DNA and body size have suggested that Black Bears (Ursus americanus) inhabiting the island of Newfoundland represent a different subspecies or ecotype from mainland populations. Assuming that body size covaries positively with skull size, we predicted that skull size would be greater for bears on the island than the mainland, and the distribution of size-related shape components in multivariate space should show a distinct separation between Newfoundland and mainland populations. Measurements of 1080 specimens from Newfoundland, Alberta, New York, and Quebec did not provide unequivocal support for our prediction that skull size in Newfoundland bears would be larger than bears from the mainland populations. After removing ontogenetic effects of skull size, between-population variation in skull shape was greater in females than males, and the analysis significantly separated Newfoundland bears from mainland populations. Explanations for this pattern are numerous, but currently remain hypothetical. Limited covariation between skull size and body size suggests that genetic traits regulating the size of Black Bear skulls are more heritable (i.e., less influenced by environmental selection pressures) than characteristics affecting body size. We hypothesize that if gape size does not limit prey size in solitary terrestrial carnivores, large degrees of among-population variation in body size should be coupled with little covariation in skull size. In general, sexual dimorphism in skull size and shape was marginal for the phenotypic characters measured in our study. We believe that sexual dimorphism in skull size in Black Bears is primarily driven by intrasexual selection in males for increased gape size display, while similarity in skull shape between sexes is associated with the constraints of a temporally-selective, but similar diet.

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The Consequences of Sexual Dimorphism in Body Size for Butterfly Flight and Thermoregulation

Functional Ecology ◽

10.2307/2389315 ◽

1990 ◽

Vol 4 (4) ◽

pp. 475 ◽

Cited By ~ 35

Author(s):

G. W. Gilchrist

Keyword(s):

Body Size ◽

Sexual Dimorphism

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Sexual dimorphism in body size and life‐history traits in a population ofTriturus alpestris alpestris

Italian Journal of Zoology ◽

10.1080/11250000409356620 ◽

2004 ◽

Vol 71 (sup2) ◽

pp. 117-120 ◽

Cited By ~ 3

Author(s):

Elena Marzona ◽

Daniele Seglie ◽

Cristina Giacoma

Keyword(s):

Life History ◽

Body Size ◽

Sexual Dimorphism ◽

Life History Traits

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Body size, female reproduction and sexual dimorphism in the lizard Ameiva ameiva (Teiidae) in a restinga of southeastern Brazil

Revista Brasileira de Zoologia ◽

10.1590/s0101-81752008000200024 ◽

2008 ◽

Vol 25 (2) ◽

pp. 370-372 ◽

Cited By ~ 6

Author(s):

Carlos Frederico Duarte Rocha

Keyword(s):

Body Size ◽

Sexual Dimorphism ◽

Clutch Size ◽

Reproductive Period ◽

Southeastern Brazil ◽

Head Width ◽

Sexually Dimorphic ◽

Female Reproduction ◽

Female Body Size ◽

Reproductive Body

In this study 57 specimens of the lizard Ameiva ameiva (Linnaeus, 1758) collected in the restinga at Barra de Maricá, in the state of Rio de Janeiro, southeastern Brazil, were analyzed to investigate size relations and reproduction (in females) and sexual dimorphism of this population. We answered the following questions: 1) what is the minimum reproductive body size in females? 2) what is the average clutch size and 3) how is clutch size related to body size? 4) Are body and head sizes sexually dimorphic? Mean clutch size was 6.7 ± 2.1 eggs and was positively correlated with female body size. Sexual dimorphism favoring males was found: adult mean snout-vent length was great in males (124.2 ± 17.8 mm) than females (96.5 ± 23.1 mm SVL), and males were larger with respect to head width and length, and body mass. Thus, despite the marked seasonality at Barra de Maricá, A. ameiva has an extended reproductive period. Also, intrasexual selection may have acted on females to produce larger clutches, and on males, favoring larger males.

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Body Size and Sexual Dimorphism

Encyclopedia of Animal Behavior ◽

10.1016/b978-0-08-045337-8.00117-0 ◽

2010 ◽

pp. 220-225

Author(s):

R.M. Cox

Keyword(s):

Body Size ◽

Sexual Dimorphism

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THE ORIGINS OF SEXUAL DIMORPHISM IN BODY SIZE IN UNGULATES

Evolution ◽

10.1111/j.0014-3820.2002.tb01438.x ◽

2002 ◽

Vol 56 (6) ◽

pp. 1276-1285 ◽

Cited By ~ 98

Author(s):

F. J. Pérez-Barbería ◽

I. J. Gordon ◽

M. Pagel

Keyword(s):

Body Size ◽

Sexual Dimorphism

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Factors driving sexual dimorphism and colour variability in the Achala Copper Lizard (Pristidactylus achalensis), an endemic species to the highland mountains in central Argentina

Canadian Journal of Zoology ◽

10.1139/cjz-2019-0293 ◽

2020 ◽

Vol 98 (6) ◽

pp. 377-389

Author(s):

S. Naretto ◽

M. Chiaraviglio

Keyword(s):

Sex Differences ◽

Spatial Distribution ◽

Body Size ◽

Sexual Dimorphism ◽

Endemic Species ◽

Morphological Changes ◽

Head Size ◽

Head Width ◽

Temporal And Spatial Distribution ◽

Central Argentina

The intensity of mating competition varies according to the temporal and spatial distribution of individuals. Measuring sexual dimorphism over time and interpreting the association between individuals is therefore important if we aim to understand how sexual traits are influenced. We examined sex differences in the Achala Copper Lizard (Pristidactylus achalensis (Gallardo, 1964)), an endemic species from the highest part of mountains of central Argentina. Over 4 years, we explored sex-specific variation in body size, head size, interlimb length, and body colouration. Furthermore, we evaluated how these traits varied temporally, and we also explored whether the spatial distribution of individuals is explained by variation in these traits. We found that P. achalensis is a species with sexual dimorphism in multiple characters, including body size, head size, and colouration. Interestingly, some traits related to mating, such as head width, show a temporal variability in both sexes, whereas other traits, such as colouration, varies seasonally only in males. Our results underline the intriguing possibility of seasonal morphological changes related to mating, and more broadly that sex differences are influenced by sexual selection pressures mediated by temporal variation in mate competition.

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