Sexual dimorphism in snake tail length: sexual selection, natural selection, or morphological constraint?

1989 ◽  
Vol 38 (2) ◽  
pp. 133-154 ◽  
Author(s):  
RICHARD B. KING
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Sexual Dimorphism ◽  
Tail Length ◽  
Morphological Constraint

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.

Heads or tails? Sexual dimorphism in helodermatid lizards

2007 ◽  
Vol 85 (1) ◽  
pp. 92-98 ◽  
Author(s):  
C.M. Gienger ◽  
Daniel D. Beck
Keyword(s):  
Sexual Selection ◽  
Body Size ◽  
Sexual Dimorphism ◽  
Morphological Traits ◽  
Tail Length ◽  
Repeated Sequences ◽  
Analysis Of Covariance ◽  
Head Size ◽  
Heloderma Suspectum

We tested the hypothesis that helodermatid lizards (Gila monsters, Heloderma suspectum Cope, 1869, and beaded lizards, H. horridum (Wiegmann, 1829)) show sexual dimorphism in morphological traits related to male–male agonistic behaviors. Male–male combat in helodermatid lizards involves repeated sequences of ritualized grappling. Male Gila monsters use their heads in attempts to gain or maintain a superior position during repeated combat bouts that may last for hours. Pairs of fighting male beaded lizards form spectacular body arches, with abdomens adpressed and snouts, forelimbs, and tail tips contacting the ground. We measured body size, head size, and tail length in 208 preserved H. suspectum, and body size and tail length (but not head size) in 79 live H. horridum, then tested for sexual dimorphism using analysis of covariance. Male Gila monsters had proportionately larger heads than females but did not differ in tail length or body size. Male beaded lizards had proportionately longer tails than females and were larger in body size only when the largest individuals were included in the analysis. Differences in head dimensions (in H. suspectum) and tail length (in H. horridum) are likely the result of sexual selection acting through male–male agonistic behaviors in this unique lizard taxon.

scholarly journals Ontogenetic allometry in the foot size of Oligoryzomys flavescens (Waterhouse, 1837) (Rodentia, Sigmodontinae)

2015 ◽  
Vol 75 (2) ◽  
pp. 435-441 ◽  
Author(s):  
R. Maestri ◽  
R. Fornel ◽  
TRO. Freitas ◽  
JR. Marinho
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Sexual Dimorphism ◽  
Encounter Rate ◽  
Allometric Growth ◽  
Positive Allometry ◽  
Rate Of Growth ◽  
Ontogenetic Allometry ◽  
Males And Females ◽  
Oligoryzomys Flavescens

Ontogenetic allometry is the study of how the size or shape of certain structures changes over the course of an animal’s development. In this study, using Huxley's formula of allometric growth (1932), we assessed the changes in the rate of growth of the feet size of the sigmodontine rodent Oligoryzomys flavescens during its ontogeny and compared differences between males and females. We find evidence of a change of polarity during the ontogenetic development of the species, with the presence of positive allometry during pregnancy and negative allometry in adulthood. Moreover, we note the presence of sexual dimorphism in the size of the feet, in which males of the species have a higher rate of growth than females. This growth pattern is positively related to escape from predators in childhood in both sexes and, in adulthood, provides a higher encounter rate of females by males, due to the larger displacement of the latter. We suggest that both the forces of natural selection and sexual selection have acted to shape the evolution of foot size in this species.

scholarly journals An Improved Approach to Measuring Sexual Dimorphism in Snakes: Morphological Variation in the Bahamian Racer (Cubophis vudii vudii)

2020 ◽  
Vol 27 (2) ◽  
pp. 137-146
Author(s):  
Scott Johnson ◽  
William K. Hayes
Keyword(s):  
Body Size ◽  
Natural Selection ◽  
Sexual Dimorphism ◽  
Linear Models ◽  
Geometric Mean ◽  
Tail Length ◽  
Head Width ◽  
Island Populations ◽  
Total Length ◽  
New Providence

Sexual dimorphism in animals exists in many forms, including overall size difference between the sexes (sexual size dimorphism, SSD) and size and structural differences in body components (sexual body component dimor­phism, SBCD). Studies of sexual dimorphism seek to determine whether dimorphic traits result from sexual selection, natural selection, or non-adaptive processes. Characterizing sexual dimorphism depends on identifying an unbiased character for overall body size, which can then be used to assess both SSD and SBCD. Most studies of snakes use snout-vent length (SVL) for this purpose, but SVL may itself be dimorphic. In this study, we examined SSD and SBCD in three island populations of the Bahamian Racer (Cubophis vudii vudii). Discriminant function analysis (DFA) showed that head width (females wider) and tail length (males longer) best discriminated between the sexes, and total length provided the least discrimination. Linear models using total length as the least-biased measure for overall size revealed an absence of SSD, but SBCD existed for head size (width 8.9% greater in females, length similar), trunk length (4.3% longer in females), and tail length (9.8% longer in males). Linear models also revealed differences among island populations for total length (New Providence < Eleuthera = Allen Cay) and head length (Allen Cay < Eleuthera < New Providence), but not head width or tail length. Extent of SBCD varied depending on choice of character to control for overall body size, with total length yielding the most female-biased values, and geometric mean, principal component 1 (PC1) of a principal components analysis, and SVL providing increasingly more male-biased values, respectively. Body condition was statistically similar for the two sexes and three seasons (spring, summer-fall, winter), but the mod­erate and large effect sizes, respectively, suggest that females were heavier than males, and both sexes were heaviest in spring. Females, which represented 64.9 of all snakes, suffered injuries disproportionately to males (19.7% and 3.1%, respectively), but no differences in sex ratio or frequency of injury existed among the island populations. Collectively, these findings illustrate the utility of using DFA and other approaches (geometric mean, PC1) to identify a relatively unbiased reference character for overall body size and suggest that sexual and natural selection interact to shape the morphology of these snakes.

scholarly journals Sexual dimorphism in the Chinese endemic speciesPachyhynobius shangchengensisFei, Qu and Wu, 1983 (Urodela: Hynobiidae)

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e6408 ◽  
Author(s):  
Jianli Xiong ◽  
Baowei Zhang ◽  
Qiangqiang Liu ◽  
Tao Pan ◽  
Jianping Gou
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Tail Length ◽  
Morphometric Data ◽  
Ecological Selection ◽  
Significant Difference ◽  
Selective Forces ◽  
Pachyhynobius Shangchengensis ◽  
Body Shapes ◽  
The Impact

Sexual dimorphism (SD) is a widespread phenomenon in most vertebrate species and is exhibited in a myriad of ways. In amphibians, sexual size dimorphism, in which females are larger than males, is the most common type, and sexual shape dimorphism varies among species. Different selection forces (sexual selection, fecundity selection, and ecological selection) that act differently upon the sexes form the consequence of SD. Thus, studies of SD provide information about the general intersexual divergence of the same species and allow insights into the impact of selective forces on the sexes. In this study, we analyzed morphometric data of the Shangcheng stout salamander,Pachyhynobius shangchengensis, an endemic and poorly known Chinese salamander, to examine sexual dimorphism in size and shape. The morphometric data included 15 characteristics of 68 females and 55 males which were analyzed using univariate and multivariate methods. A significant difference was found between the sexes in terms of both body size (snout-vent length) and some body shapes (e.g., head length and width, tail length and width, distance between limbs, and limb length and width) in this salamander. The longer snout-vent length in males may be attributed to sexual selection, longer and wider head in males may contribute to male-male competition, longer and wider tail in males may be attributed to energy storage and reproductive success, the larger distance between limbs in females is likely due to a fecundity advantage, and longer and more robust limbs in males may be related to reproductive or competitive behaviors. These results demonstrated that sexual dimorphism of different morphological traits is the consequence of different selection forces that act differently upon the sexes.

Darwinian Evolutionary Theory

2018 ◽  
Author(s):  
Michael Ruse
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Middle Class ◽  
Evolutionary Theory ◽  
Scientific Community ◽  
Homo Sapiens ◽  
Origin Of Species ◽  
Theory Of Evolution ◽  
Descent Of Man

Charles Robert Darwin, the English naturalist, published On the Origin of Species in 1859 and the follow-up work The Descent of Man in 1871. In these works, he argued for his theory of evolution through natural selection, applying it to all organisms, living and dead, including our own species, Homo sapiens. Although controversial from the start, Darwin’s thinking was deeply embedded in the culture of his day, that of a middle-class Englishman. Evolution as such was an immediate success in scientific circles, but although the mechanism of selection had supporters in the scientific community (especially among those working with fast-breeding organisms), its real success was in the popular domain. Natural selection, and particularly the side mechanism of sexual selection, were known to all and popular themes in fiction and elsewhere.

scholarly journals Natural selection increases female fitness by reversing the exaggeration of a male sexually selected trait

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Kensuke Okada ◽  
Masako Katsuki ◽  
Manmohan D. Sharma ◽  
Katsuya Kiyose ◽  
Tomokazu Seko ◽  
...  
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Experimental Evolution ◽  
Genetic Correlations ◽  
Lifetime Reproductive Success ◽  
Fundamental Theory ◽  
Female Fitness ◽  
Male Trait ◽  
Flour Beetles ◽  
Male Specific

AbstractTheory shows how sexual selection can exaggerate male traits beyond naturally selected optima and also how natural selection can ultimately halt trait elaboration. Empirical evidence supports this theory, but to our knowledge, there have been no experimental evolution studies directly testing this logic, and little examination of possible associated effects on female fitness. Here we use experimental evolution of replicate populations of broad-horned flour beetles to test for effects of sex-specific predation on an exaggerated sexually selected male trait (the mandibles), while also testing for effects on female lifetime reproductive success. We find that populations subjected to male-specific predation evolve smaller sexually selected mandibles and this indirectly increases female fitness, seemingly through intersexual genetic correlations we document. Predation solely on females has no effects. Our findings support fundamental theory, but also reveal unforseen outcomes—the indirect effect on females—when natural selection targets sex-limited sexually selected characters.

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