Interspecific variation in sexual dimorphism in brain size in Nearctic ground squirrels (Spermophilus spp.)

2001 ◽  
Vol 79 (5) ◽  
pp. 759-765 ◽  
Author(s):  
Andrew N Iwaniuk
Keyword(s):  
Sex Differences ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Ground Squirrel ◽  
Mating Systems ◽  
Resource Competition ◽  
Brain Size ◽  
Ground Squirrels ◽  
Detailed Knowledge ◽  
Size Dimorphism

A possible relationship between sexual dimorphism in brain size and mating system was investigated in five ground squirrel species: Spermophilus lateralis, S. tridecemlineatus, S. richardsonii, S. columbianus, and S. parryii. Relative brain size was measured by determining the endocranial volume of 247 ground squirrel skulls and regressing these values against two measurements of body size: mass and length. Analyses of covariation in the brain size / body size relationship within the five species revealed that sexual brain-size dimorphism occurs in three of the five species: S. lateralis, S. richardsonii, and S. tridecemlineatus. Application of a reduced major axis regression model indicated, however, that only S. lateralis and S. richardsonii exhibit significant sexual brain-size dimorphism. These findings suggest that the degree of sexual brain-size dimorphism is not directly correlated with variation in mating systems. Spatial abilities may play a role in the evolution of sexual brain-size dimorphism in ground squirrels, but the spatial requirements of mating systems appear to be insufficient. The possibility of sex differences in cognition, resource competition, and other variables as contributory factors to the evolution of sexual brain-size dimorphism is offered, but detailed knowledge of sex differences in the behaviour of ground squirrels is required to provide a definitive answer.

Body size, brain size, and sexual dimorphism in Homo naledi from the Dinaledi Chamber

2017 ◽  
Vol 111 ◽  
pp. 119-138 ◽  
Author(s):  
Heather M. Garvin ◽  
Marina C. Elliott ◽  
Lucas K. Delezene ◽  
John Hawks ◽  
Steven E. Churchill ◽  
...  
Keyword(s):  
Body Size ◽  
Sexual Dimorphism ◽  
Brain Size

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

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.

Growth, maturity, and sexual dimorphism in the wood turtle, Clemmys insculpta

1990 ◽  
Vol 68 (4) ◽  
pp. 672-677 ◽  
Author(s):  
Jeffrey E. Lovich ◽  
Carl H. Ernst ◽  
John F. McBreen
Keyword(s):  
Body Size ◽  
Sexual Dimorphism ◽  
Carapace Length ◽  
Sexual Size Dimorphism ◽  
Von Bertalanffy ◽  
Size Dimorphism ◽  
Adult Females ◽  
Body Sizes ◽  
Von Bertalanffy Growth Model ◽  
Wood Turtle

Growth in the wood turtle (Clemmys insculpta) is described using the von Bertalanffy growth model and nonlinear regression. Growth in both sexes is similar until about 160 mm plastron length. Males grew at a faster rate after this size. Males appear to mature at a larger size and later age than females, although age-specific body size is highly variable. Sexual size dimorphism, in carapace length, is pronounced, with males attaining mean body sizes significantly larger (1.07–1.10 times) than those of adult females. Plastron length is an inappropriate measure of sexual size dimorphism because of the development of plastral concavity in males. Females tend to predominate in samples, possibly owing to differential maturity of the sexes. The direction of sexual size dimorphism may be maintained by intrasexual competition among males for access to females. Data for several adults captured at intervals of from 9 to 20 years support the concept of indeterminate growth.

scholarly journals Mass-mediated sex differences in climbing patterns support the gravity hypothesis of sexual size dimorphism

Web Ecology ◽  
2007 ◽  
Vol 7 (1) ◽  
pp. 106-112 ◽  
Author(s):  
J. Moya-Laraño ◽  
D. Vinković ◽  
C. M. Allard ◽  
M. W. Foellmer
Keyword(s):  
Sex Differences ◽  
Body Size ◽  
Sexual Size Dimorphism ◽  
Negative Relationship ◽  
Simulated Data ◽  
Statistical Efficiency ◽  
Data Set ◽  
Size Dimorphism ◽  
Significant Negative Relationship ◽  
Gravity Hypothesis

Abstract. The gravity hypothesis of sexual size dimorphism can explain the patterns of extreme sexual size dimorphism in spiders (males smaller than females) because small males climb faster and therefore may be better at reaching females that live in high habitats. Recently, the main prediction of a negative relationship between climbing speed and body size in spiders has been called into question. Here we induced males and females of the spider Leucauge venusta (Tetragnathidae) to run on vertical surfaces and found partial support for the gravity hypothesis. As predicted, males climb faster than females and we demonstrated that this effect is an indirect effect mediated by the negative relationship between body mass and climbing speed. We validate our results using simulated data showing that there is enough statistical efficiency in our data set to support our conclusions. We distinguished between direct and indirect effects (through mass) on sex differences in climbing speed by means of path analysis. Thus, we provide empirical evidence that by being smaller, males are able to climb faster than females. However, we found only a barely significant negative relationship between climbing speed and body size when only males were considered. Reasons for such results are discussed within the text.

Patterns of intraspecific aggression inferred from injuries in an aquatic turtle with male-biased size dimorphism

2017 ◽  
Vol 95 (6) ◽  
pp. 393-403 ◽  
Author(s):  
M.G. Keevil ◽  
B.S. Hewitt ◽  
R.J. Brooks ◽  
J.D. Litzgus
Keyword(s):  
Body Size ◽  
Resource Competition ◽  
Adult Males ◽  
Intraspecific Aggression ◽  
Sexual Competition ◽  
Size Dimorphism ◽  
Direct Competition ◽  
Primary Driver ◽  
Coercive Mating ◽  
Provincial Park

Patterns of sexual size dimorphism (SSD) in turtles are correlated with ecological mode, and it has been hypothesized that mating systems are also shaped by ecological mode. Male combat and coercive mating are competing explanations for male-biased SSD, but are difficult to assess empirically in aquatic species with cryptic behaviour. We quantified SSD and compiled observations of putative combat wounds collected from over 500 captures of Snapping Turtles (Chelydra serpentina (L., 1758)) in Algonquin Provincial Park, Ontario, to test hypotheses of mate competition and coercion. We found that both sex and body size were important predictors of risk of wounding, consistent with the hypothesis that male–male sexual competition is the primary driver of intraspecific aggression. Low wounding rates among females suggests that resource competition and coercive mating are not important causes of injuries. The risk of wounding increased monotonically with body size in adult males but not in adult females, and small males were less likely to be injured, suggesting that they employ a risk-averse strategy by avoiding direct competition for mates. There was no evidence of asymptotic or decreasing wounding probability in the largest males, which is consistent with the hypothesis that large males compete most intensively to monopolize mates.

Differences in sexual dimorphism among four gazelle taxa (Gazella spp.) in the Middle East

2010 ◽  
Vol 60 (4) ◽  
pp. 395-412 ◽  
Author(s):  
Peter Cunningham ◽  
Martin Plath ◽  
Torsten Wronski ◽  
Mohamed Sandouka
Keyword(s):  
Body Weight ◽  
Sexual Selection ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Mating Systems ◽  
Research Centre ◽  
Sexually Dimorphic ◽  
Male Sex ◽  
The Difference ◽  
Horn Development

AbstractSexual selection can lead to sexual dimorphism, where elaborated traits used in mate attraction or weaponry are more expressed in the male sex. The degree of sexual dimorphism, however, is known to vary even among closely related taxa. Here we examined sexual dimorphism in horn length and three measures related to body size (body weight, shoulder height, and neck circumference) in four gazelle taxa, representing at least three species, i.e. Dorcas gazelle (G. dorcas), Sand gazelle (G. subgutturosa marica) and Mountain gazelle (G. gazella). The latter is represented by two distinctive phenotypes maintained and bred at the King Khalid Wildlife Research Centre in Saudi Arabia. We describe marked differences in sexual dimorphism among taxa. For example, the difference in sexually dimorphic horn development was driven primarily by females exhibiting pronounced differences in horn development. We discuss how divergent mating systems, and group sizes affect these differences among the examined taxa, with more competition in larger groups probably promoting the evolution of larger horns in females, thereby leading to less sexual dimorphism.

Race, Brain Size, and Intelligence: A Reply to Cernovsky

1990 ◽  
Vol 66 (2) ◽  
pp. 659-666 ◽  
Author(s):  
J. Philippe Rushton
Keyword(s):  
Sex Differences ◽  
Body Size ◽  
Evolutionary Theory ◽  
Reproductive Strategies ◽  
Additional Data ◽  
Brain Size ◽  
Autopsy Study

Cernovsky's 1990 critique of my work on the relation between brain size and IQ inadequately presents my position. I did not address the issue of sex differences in brain size nor did I conclude that “women are less intelligent than men” (p. 337). In the autopsy study cited by Cernovsky, it was concluded that, when body size is controlled, the male-female difference in brain size is removed but the black-white difference in brain size remains. Cernovsky also ignores much additional data, including that Mongoloid populations have larger and heavier brains than Caucasoids. Here, I review evidence on the relation between (a) brain size and race and (b) brain size and intelligence. Data are also tabulated for personality, speed of maturation, and sexuality, on all of which the Caucasoid average consistently falls between those of Mongoloids and Negroids. This ordering may be explained by a gene-based evolutionary theory of r/K reproductive strategies in which Mongoloids are more K-selected than Caucasoids and Caucasoids more than Negroids.

scholarly journals Sexual Size Dimorphism in Stone Marten (MARTES Foina, Erxl. 1777) from Sarnena Sredna Gora Mts (BULGARIA)

2019 ◽  
Vol 17 (4) ◽  
pp. 318-322
Author(s):  
S. Peeva
Keyword(s):  
Body Size ◽  
Sexual Dimorphism ◽  
Sexual Size Dimorphism ◽  
Tail Length ◽  
Stone Marten ◽  
Martes Foina ◽  
Size Dimorphism

Sexual dimorphism in body size measurements of 65 stone martens was investigated in winter periods (10.12.- 01.03) 2013 to 2017. There was found sexual dimorphism in body size of Stone Marten from Central Bulgaria: males were larger than females. The tail length (with or without hairs) did not depend on sex. The sexual dimorphism in the most variable linear parameters of the species varied from 2.76% to 10.63%. Male stone martens were 23.37% heavier than females.

Sign in / Sign up

Export Citation Format

Share Document