Sexual dimorphism and distorted sex ratios in spiders

Nature ◽  
1992 ◽  
Vol 360 (6400) ◽  
pp. 156-159 ◽  
Author(s):  
Fritz Vollrath ◽  
Geoff A. Parker
Keyword(s):  
Sexual Dimorphism ◽  
Sex Ratios

Female and male costs of reproduction must be equal in dioecious Cape plant genus Leucadendron (Proteaceae)

2019 ◽  
Vol 67 (7) ◽  
pp. 517
Author(s):  
Jeremy J. Midgley ◽  
Adam G. West ◽  
Michael D. Cramer
Keyword(s):  
Sexual Dimorphism ◽  
Reproductive Output ◽  
Sex Ratios ◽  
Reproductive Allocation ◽  
Costs Of Reproduction ◽  
Male And Female

The Cape Leucadendron genus is dioecious, with extreme vegetative dimorphism displayed in some species – females having much larger leaves and fewer branches than males – whereas other species are monomorphic. Leucadendron is ecologically diverse, with some species with canopy stored seeds (serotiny) and others with soil stored seeds. These features mean that the Cape Leucadendron is an ideal genus to study the costs of reproduction for the different sexes in plants, and to determine whether vegetative dimorphism could be due to unequal costs. Here we use the unique aspects of the fire-prone Cape environment in which leucadendrons occur to show that the costs of sex must be equal between the sexes. Leucadendron populations are single aged because they only recruit after fires that kill all adults. Therefore, because the sexes have the same lifespans, they must have the same lifetime extent of vegetative versus reproductive allocation. Also, ecologically similar hermaphrodite Proteaceae co-exist with dioecious taxa. To co-occur, dioecious and hermaphrodite taxa must have the same mean post-fire fitness. This implies that dioecious females must have double the reproductive output that a co-occurring hermaphrodite has. This is only possible if the costs of reproduction are the same for the sexes and that the sexes use the same resources for reproduction. Finally, because males and female co-occur, they must be competitively equivalent to maintain natal sex ratios. These three factors suggest male and female allocate equivalently and therefore that vegetative sexual dimorphism is unlikely to be due to differences in allocation.

Sex Ratios, Sexual Selection, and Sexual Dimorphism in Quails

1980 ◽  
Vol 44 (1) ◽  
pp. 198 ◽  
Author(s):  
David E. Brown ◽  
R. J. Gutierrez
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Sex Ratios

scholarly journals Developmental sexual dimorphism and the evolution of mechanisms for adjustment of sex ratios in mammals

2016 ◽  
Vol 1389 (1) ◽  
pp. 147-163 ◽  
Author(s):  
Elissa Z. Cameron ◽  
Amy M. Edwards ◽  
Laura M. Parsley
Keyword(s):  
Sexual Dimorphism ◽  
Sex Ratios

scholarly journals Sex ratios, size distributions, and sexual dimorphism in the dioecious tree Ilex aquifolium (Aquifoliaceae)

1998 ◽  
Vol 85 (11) ◽  
pp. 1602-1608 ◽  
Author(s):  
Jose´ Ramo´n Obeso ◽  
Manuel Alvarez-Santullano ◽  
Rube´n Retuerto
Keyword(s):  
Sexual Dimorphism ◽  
Sex Ratios ◽  
Size Distributions ◽  
Ilex Aquifolium

scholarly journals Models of sex-ratio meiotic drive and sexual selection in stalk-eyed flies

1999 ◽  
Vol 74 (3) ◽  
pp. 245-253 ◽  
Author(s):  
RUSSELL LANDE ◽  
GERALD S. WILKINSON
Keyword(s):  
Sexual Selection ◽  
Sexual Dimorphism ◽  
Sex Ratio ◽  
Sex Ratios ◽  
Meiotic Drive ◽  
Total Body Length ◽  
Complete Suppression ◽  
Male Character ◽  
Female Mating ◽  
Female Mating Preferences

Hypertrophied sexually dimorphic eye stalks have evolved independently in several families of Diptera, with the eyespan of males exceeding their total body length in some species. These structures function in intermale contests for territories and in mate attraction, the classical mechanisms of sexual selection. In the family Diopsidae, species with extremely exaggerated eye stalks and marked sexual dimorphism in relative eyespan also usually have strongly female-biased sex ratios in nature caused by X-linked meiotic drive, whereas species with relatively small eye stalks have little or no sexual dimorphism, often lack meiotic drive and have even sex ratios. We investigate the possible connection between sexual selection and sex-ratio meiotic drive by analysing a three-locus model for the evolution of female choice for a male character associated with meiotic drive. Both meiotic drive and the male character are X-linked and the female preference is autosomal. Our model shows that suppressed recombination between meiotic drive and the male character, e.g. by inversion of the X chromosome, is necessary for sex-ratio selection to promote the origin of female mating preferences and exaggerated secondary sexual characters. With complete suppression of recombination, sexual selection reduces the frequency of meiotic drive, and may eliminate it. Very rare recombination, gene conversion or mutation, at rates characteristic of chromosome inversions in Drosophila, restores the meiotic drive polymorphism to its original equilibrium. Sex-ratio meiotic drive may thus act as a catalyst accelerating the origin of female mating preference and exaggerated male traits.

Prenatal sex ratios influence sexual dimorphism in a reptile

2003 ◽  
Vol 295A (2) ◽  
pp. 183-187 ◽  
Author(s):  
Tobias Uller ◽  
Mats Olsson
Keyword(s):  
Sexual Dimorphism ◽  
Sex Ratios

Mixture Analysis and Mammalian Sex Ratio Among Middle Pleistocene Mouflon of Arago Cave, France

1999 ◽  
Vol 52 (2) ◽  
pp. 259-268 ◽  
Author(s):  
Hervé Monchot
Keyword(s):  
Sexual Dimorphism ◽  
Maximum Likelihood ◽  
Sex Ratio ◽  
Statistical Approach ◽  
Sex Ratios ◽  
Middle Pleistocene ◽  
Mixture Analysis ◽  
Method Of Maximum Likelihood ◽  
Early Humans ◽  
Hunting Strategy

In archaeological studies, it is often important to be able assess sexual dimorphism and sex ratios in populations. Obtaining sex ratio is easy if each individual in the population can be accurately sexed through the use of one more objective variables. But this is often impossible, due to incompleteness of the osteological record. A modern statistical approach to handle this problem is Mixture Analysis using the method of maximum likelihood. It consists of determining how many groups are present in the sample, two in this case, in which proportions they occur, and to estimate the parameters accordingly. This paper shows the use of this method on vertebrate fossil populations in a prehistoric context with implications on prey acquisition by early humans. For instance, the analysis of mouflon bones from Arago cave (Tautavel, France) indicates that there are more females than males in the F layer. According to the ethology of the animal, this indicates that the hunting strategy could be the result of selective choice of the prey. Moreover, we may deduce the presence of Anteneandertalians on the site during spring and summer periods.

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