A Shape to Die for?

2021 ◽  
pp. 481-510
Author(s):  
Graham Mitchell
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Surface Water ◽  
Alternative Hypothesis ◽  
Natural Habitat ◽  
Large Body ◽  
Male And Female ◽  
Large Size ◽  
Selection For ◽  
Competition For Resources

The product of natural selection over at least 15 million years is the elongated, slender shape of giraffes that fits the natural habitat giraffes now occupy. What selection pressures operated to produce their shape? Their shape is partly the product of gravity and could have been an accidental by-product of selection for a large body mass and the protection from predation that large size brings, but the prevailing explanation is that their shape confers a browsing advantage. Preferred browse is concentrated at a height easily reached by giraffes but not by other browsers and natural selection would have favored those giraffes that could reach it. An alternative hypothesis is that their shape confers thermoregulatory benefits in addition to improved vigilance. Another hypothesis is that a long neck evolved to counter long legs allowing giraffes to drink surface water. An attractive hypothesis is that their shape is a product of ‘runaway’ sexual selection by females for males with long heavy necks, but analysis of this hypothesis has shown that the morphology of male and female giraffe does not differ. Nevertheless, all these possibilities could have contributed. A consequence of selection for their shape is over-specialization: giraffes seem to be inextricably dependent on a narrow diet, a diet that is subject to the vagaries of climate and competition for resources. The greatest threat to their survival is, therefore, their shape.

Differences in male and female cognitive abilities: Sexual selection or division of labor?

1996 ◽  
Vol 19 (2) ◽  
pp. 254-255
Author(s):  
Michael T. Ghiselin
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Sexual Dimorphism ◽  
Division Of Labor ◽  
Cognitive Abilities ◽  
Reproductive Competition ◽  
Male And Female ◽  
Males And Females

AbstractIn Darwinian terminology, “sexual selection” refers to purely reproductive competition and is conceptually distinct from natural selection as it affects reproduction generally. As natural selection may favor the evolution of sexual dimorphism by virtue of the division of labor between males and females, this possibility needs to be taken very seriously.

scholarly journals Understanding sex differences in the cost of terrestrial locomotion

2011 ◽  
Vol 279 (1729) ◽  
pp. 826-832 ◽  
Author(s):  
John J. Lees ◽  
Robert L. Nudds ◽  
Lars P. Folkow ◽  
Karl-Arne Stokkan ◽  
Jonathan R. Codd
Keyword(s):  
Sex Differences ◽  
Sexual Selection ◽  
Male And Female ◽  
Locomotor System ◽  
Terrestrial Locomotion ◽  
Female Data ◽  
Selection For ◽  
Morphological Differences ◽  
Lagopus Muta ◽  
The Cost

Little is known regarding the physiological consequences of the behavioural and morphological differences that result from sexual selection in birds. Male and female Svalbard rock ptarmigans ( Lagopus muta hyperborea ) exhibit distinctive behavioural differences during the breeding season. In particular, males continuously compete for and defend territories in order to breed successfully, placing large demands on their locomotor system. Here, we demonstrate that male birds have improved locomotor performance compared with females, showing both a lower cost of locomotion (CoL) and a higher top speed. We propose that the observed sex differences in locomotor capability may be due to sexual selection for improved male performance. While the mechanisms underlying these energetic differences are unclear, future studies should be wary when pooling male and female data.

Multiple sire mating in swine; evidence of natural selection for mating efficiency

1961 ◽  
Vol 56 (1) ◽  
pp. 31-37 ◽  
Author(s):  
Lavon J. Sumption
Keyword(s):  
Natural Selection ◽  
Mating Behaviour ◽  
Animal Breeding ◽  
Evolutionary Significance ◽  
Mating Frequency ◽  
Combined Effects ◽  
Male And Female ◽  
Female Mating ◽  
Mating Efficiency ◽  
Selection For

Evidence of natural selection for certain aspects of mating efficiency in swine are advanced based on preliminary studies with thirty-one sires, fiftyeight dams and their progeny. Selective fertilization was conclusively demonstrated. Variations in male and female mating behaviour were sufficiently large to indicate considerable non-randomness of mating frequency under the conditions of multiple sire mating (i.e. group exposure of dams to selected sires). The combined effects of the separate phenomena of selective fertilization and mating behaviour are discussed in relation to their evolutionary significance in animal breeding.

scholarly journals Natural and sexual selection act on different axes of variation in avian plumage color

2015 ◽  
Vol 1 (2) ◽  
pp. e1400155 ◽  
Author(s):  
Peter O. Dunn ◽  
Jessica K. Armenta ◽  
Linda A. Whittingham
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Habitat Type ◽  
Sexual Differences ◽  
Plumage Color ◽  
Evolutionary Transitions ◽  
Testes Size ◽  
Selection For ◽  
Bird Coloration ◽  
Natural And Sexual Selection

The bright colors of birds are often attributed to sexual selection on males, but in many species both sexes are colorful and it has been long debated whether sexual selection can also explain this variation. We show that most evolutionary transitions in color have been toward similar plumage in both sexes, and the color of both sexes (for example, bright or dull) was associated with indices of natural selection (for example, habitat type), whereas sexual differences in color were primarily associated with indices of sexual selection on males (for example, polygyny and large testes size). Debate about the evolution of bird coloration can be resolved by recognizing that both natural and sexual selection have been influential, but they have generally acted on two different axes: sexual selection on an axis of sexual differences and natural selection on both sexes for the type of color (for example, bright or dull).

scholarly journals Sexual selection drives the evolution of wing interference patterns

2018 ◽  
Author(s):  
MF Hawkes ◽  
E Duffy ◽  
R Joag ◽  
A Skeats ◽  
J Radwan ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Digital Imaging ◽  
Colour Vision ◽  
Species Recognition ◽  
Sexual Attractiveness ◽  
Courtship Display ◽  
Structural Coloration ◽  
Male And Female ◽  
Selection For ◽  
First Time

AbstractThe seemingly transparent wings of many insects have recently been found to display dramatic structural coloration. These structural colours (wing interference patterns: WIPs) may be involved in species recognition and mate choice, yet little is known about the evolutionary processes that shape them. Additionally, existing research has been restricted by analysing WIPs without due consideration of how they are actually perceived by the viewers’ colour vision. Here, we use multispectral digital imaging and a model ofDrosophilavision to compare WIPs of male and femaleDrosophila simulansfrom replicate populations forced to evolve with or without sexual selection for 68 generations. We show for the first time that WIPs modelled inDrosophilavision evolve in response to sexual selection, and confirm that WIPs correlate with male sexual attractiveness. These findings add a new element to the otherwise well describedDrosophilacourtship display and confirm that wing colours evolve through sexual selection.

scholarly journals Sexual size dimorphism and sexual selection in artiodactyls

2020 ◽  
Vol 31 (3) ◽  
pp. 792-797
Author(s):  
Marcelo H Cassini
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Group Size ◽  
Sexual Size Dimorphism ◽  
Alternative Hypothesis ◽  
Mammalian Species ◽  
Generalized Least Squares ◽  
Size Dimorphism ◽  
Selection For

Abstract Sexual size dimorphism is biased toward males in most mammalian species. The most common explanation is precopulatory intramale sexual selection. Large males win fights and mate more frequently. In artiodactyls, previous tests of this hypothesis consisted of interspecific correlations of sexual dimorphism with group size as a surrogate for the intensity of sexual selection (Is). However, group size is not a proper measure of sexual selection for several reasons as is largely recognized in other mammalian taxa. I conducted an interspecific test on the role of sexual selection in the evolution of sexual dimorphism using the variance in genetic paternity as a proxy for the Is. I reviewed the literature and found 17 studies that allowed estimating Is= V/(W2), where V and W are the variance and mean number of offspring per male, respectively. A phylogenetic generalized least squares analysis indicated that dimorphism (Wm/Wf) showed a significant positive regression with the intensity of sexual selection but not group size (multiple r2= 0.40; F3,17= 12.78, P = 0.002). This result suggests that sexual selection may have played a role in the evolution of sexual size dimorphism in Artiodactyla. An alternative hypothesis based on natural selection is discussed.

scholarly journals Sexual selection drives the evolution of male wing interference patterns

2019 ◽  
Vol 286 (1903) ◽  
pp. 20182850 ◽  
Author(s):  
M. F. Hawkes ◽  
E. Duffy ◽  
R. Joag ◽  
A. Skeats ◽  
J. Radwan ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Digital Imaging ◽  
Colour Vision ◽  
Species Recognition ◽  
Sexual Attractiveness ◽  
Courtship Display ◽  
Structural Coloration ◽  
Male And Female ◽  
Male Wing ◽  
Selection For

The seemingly transparent wings of many insects have recently been found to display unexpected structural coloration. These structural colours (wing interference patterns: WIPs) may be involved in species recognition and mate choice, yet little is known about the evolutionary processes that shape them. Furthermore, to date investigations of WIPs have not fully considered how they are actually perceived by the viewers' colour vision. Here, we use multispectral digital imaging and a model of Drosophila vision to compare WIPs of male and female Drosophila simulans from replicate populations forced to evolve with or without sexual selection for 68 generations. We show that WIPs modelled in Drosophila vision evolve in response to sexual selection and provide evidence that WIPs correlate with male sexual attractiveness. These findings add a new element to the otherwise well-described Drosophila courtship display and confirm that wing colours evolve through sexual selection.

Natural selection drives the link between male immune function and reproductive potential

2005 ◽  
Vol 83 (7) ◽  
pp. 1012-1014 ◽  
Author(s):  
Kenneth M Fedorka ◽  
Marlene Zuk ◽  
Timothy A Mousseau
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Reproductive Potential ◽  
Nuptial Gift ◽  
Honest Signal ◽  
Male Behavior ◽  
Nuptial Gifts ◽  
The Gift ◽  
Selection For ◽  
Allonemobius Socius

In the ground cricket Allonemobius socius (Scudder 1877), males provide females with a hemolymph-based nuptial gift. The size of the gift depends on when copulation is terminated, which can be controlled by either sex. Here we show that more immunocompetent males provide larger nuptial gifts, increasing their reproductive potential. To address if this pattern was the consequence of sexual selection for an honest signal (i.e., females assess mate immune quality through the hemolymph), we examined which sex controlled gift size. We found that the probability that males initiated the end of copulation increased when gift size was small (stereotypical of less immunocompetent males). Thus, early termination of copulation was the consequence of male behavior, suggesting that the association between immunocompetence and gift size was not due to sexual selection, but to natural selection for male vigor.

Sex, Difference, and Desire

2020 ◽  
pp. 177-232
Author(s):  
Ben Bradley
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Evolutionary Psychology ◽  
Evolutionary Biology ◽  
Racial Politics ◽  
Sexual Agency ◽  
Human History ◽  
Male And Female ◽  
Males And Females ◽  
Descent Of Man

The parts of The Descent of Man dealing with sexual desire and difference have sparked more controversy and misrepresentation than any of Darwin’s other publications. Crucial to Descent’s arguments is the derivation of sexual selection from the dramas of display and desire observed among animals. The book describes four plotlines structuring the theatre of sexual agency in animals, each having different implications for the roles played by males and females. When Descent extends these plotlines to humans, they alter and modulate into an even more varied array of scenarios, again, each with its own distinctive roles for women and men. A mirror-dynamic figures centrally in both animal and human sex—the need to recognize or predict others’ desires so as to act in a way to arouse them. However, several nodes of concern disturb Darwin’s presentation of human sex: tensions between his three epochs of human history; Victorian racial politics; Victorian ideas about male and female superiority; and the imperatives of propriety. The chapter illustrates some of the muddles that result from these concerns, including: confirmation bias; aporia in argument; grammatical kinks; and overlap between sexual and natural selection. Finally, the chapter instances some of the main resonances in more recent scholarship of Darwin’s discussion of sex, instancing debates in feminism, about anthropomorphism, in evolutionary biology, and evolutionary psychology.

scholarly journals Saccadic head rotations during walking in the stalk-eyed fly ( Cyrtodiopsis dalmanni )

2009 ◽  
Vol 276 (1662) ◽  
pp. 1643-1649 ◽  
Author(s):  
Gal Ribak ◽  
Alison R Egge ◽  
John G Swallow
Keyword(s):  
Sexual Selection ◽  
Angular Velocity ◽  
Head Rotation ◽  
Rotation Velocity ◽  
The Body ◽  
Male And Female ◽  
Surrounding Environment ◽  
Male Head ◽  
Selection For ◽  
Head Rotations

In stalk-eyed flies (Diopsidae), the eyes are positioned at the end of rigid peduncles protruding laterally from the head. Sexual selection for eye span in male Cyrtodiopsis dalmanni results in eye span that exceeds body length and exceeds the eye span of females. We studied whether the twofold higher moment of inertia (MOI) of the male head results in a reduced head rotation velocity during turning. We analysed films of flies performing walking turns and compared the head kinematics between the sexes. The significance of head rotation to turning was evaluated from the turning kinematics of flies with immobilized (glued) heads. Male and female C. dalmanni rotated their heads relative to the surrounding environment 1.55-fold (male) and 1.65-fold (female) faster than the angular velocity of the body by performing rapid head saccades. During the larger turns, flies with immobilized heads were unable to reorient gaze as fast as the control flies. Despite the larger MOI of the head, male C. dalmanni match the head saccade of females suggesting that eye span elongation is coupled by an adaptation of the neck apparatus to rotate the wider head.

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