Theory of Asynchronous Evolution

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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.

 

 

Copyright 2005-2009 S. Geodakyan. All rights reserved.

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