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The Evolutionary Theory of
Sex:
Sexual Dimorphism Within One Generation in Changing Environment
Let’s assume that the initial
distribution of genotypes in the population is equal for
male and female zygotes, thus the sexual dimorphism is
absent.
In
changing environment (when the ecological niche is “moving”)
the phenotypical distribution of the male sex before
selection approximately follows initial genotypic one (Figure
g). Wider
reaction norm of female sex leads to a shift in phenotype
distribution and to an appearance of temporary,
phenotipical sexual dimorphism (Figure
f). Again female
sex can leave selection zone and preserve past genotype
spectra. Males can not leave dangerous area and undergo
selection. Number of males and their genotypic variation is
decreasing after selection (Figure
q). The transformation of
the genetic information involves variation of the sexes, as
well as the modal values: the reaction norm creates
temporary, phenotypical dimorphism, selection—genotypic (Figure
f,q).
Figure.
Transformation of genetic information in one generation (n)
in changing (D) environment.
X—genotypes or phenotypes, p—their frequencies in
population. Dashed lines—male sex, reaction norm—β;
dotted lines—female sex, reaction norm—γ.
█—eliminated by natural selection (mainly male sex).
░—rejected
by sexual selection (male sex only). Distributions:
g—genotypes received from generation n-1 (zygotes);
f—phenotypes, realized from g (before and after selection);
q—genotypes transmitted to generation n+1;
v—genotypes received from generation n (zygotes). PSD—phenotypic
sexual dimorphism (temporary),
GSD—genotypical (temporary), gsd—genotypical (real).
Due to selection, number of mothers,
as a rule is always higher then number of fathers. But wide
“channel crossection” allows males to fertilize many
females and preserve the number of progeny intact. The
amounts of genetic information transmitted by the male and
female sex are approximately equal, because each child has
one father and one mother. But the structure of this
information is different. Female sex is transmitting wide
spectra of more representative information about the past
(about genotype distribution in previous
generations—constant, phylogenetic memory of the species).
Male sex—narrow spectra of more selective (but replicated)
ecological information about the present (temporary,
ontogenetic memory of the species).
In changing environment (D)
the transformation of the genetic information involves
variation of the sexes, as well as the modal values: the
reaction norm creates temporary, phenotypical dimorphism,
selection—genotypic (Figure
f,q). Male sex is getting new ecological
information. Is this difference gets leveled at
fertilization or gets preserved? The existence of the
reciprocal effects suggest that at least a portion of
genetic information stays in the male subsystem and is not
transferred into female one. Some genetic mechanisms exist
that prevent complete mixing of all genetic information.
They disturb the stochastic distribution of information from
parents to the progeny of the same sex during fertilization.
So, in changing environment,
different reaction norm and channel to the progeny create
genotypic sexual dimorphism in the first generation (Figure
v). Genotypic sexual
dimorphism then increases in the sequence of
generations.
Continue to :
Dimorphism and Dichronism in Phylogeny
More about Sexual Dimorphism:
Sexual
dimorphism. Geodakyan V. A. In: Evolution and
morphogenesis. (Mlikovsky J., Novak V. J. A., eds.),
Academia, Praha, 1985, p. 467–477.
Sexual Dimorphism is a Consequence of any Selection.
Geodakjan V. A. Towards a New Synthesis in Evolut. Biol.
Proc. Intern. Symp. Praha. 1987. Czech. Acad. Sci. p.
168–170.
Evolutionary Chromosomes And Evolutionary Sex Dimorphism.
Geodakyan V. A. Biology Bulletin, 2000, v. 27, № 2,
p. 99–113. Translated from Izvestija Akademii Nauk, Serija
Biologicheskaya, No. 2, pp. 133-148, 2000.
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