XV.7 Sexual selection also occurs in plants

The conspicuous flowers of angiosperm plants can also be considered to be a product of sexual selection. These structures are also formed primarily as a result of sexual competition, during which the individual plants “attempt” to attract pollinators more effectively than their competitors. If it were not for this competition, the plants would probably form much smaller flowers that would be less cost-intensive for the plant and that would fulfill their function equally well.

            Compared to fauna, angiosperm plants exhibit a very fundamental difference. While fauna compete in reproduction only with members of the same sex of their own species, sexual selection in flowering plantsis mediated by pollinators. They can visit the flowers of a number of other species, so the plants compete in reproduction, not only with the members of their own species, but also with the members of other species. Intraspecific sexual selection is mingled with interspecific competition and it is very difficult to differentiate between the two components.

         The participation of another species, i.e. the pollinators, in sexual selection has another interesting consequence from the viewpoint of the theory of sexual selection. The classical Fisher mechanism of fixation of genes for preference for a secondary sexual trait (XV.5.1) cannot be active in the plant-pollinator system and the mechanism of coevolutionary lift in speciation (XXI.5.6) can also not be applicable here. Genes for preference for a certain secondary sexual trait are located in a different gene pool (that of the pollinator) than the genes for the preferred trait, so that they cannot become fixed simultaneously with fixation of the preferred trait.

            Sexual selectionmediated by pollinators is understandably not the only type of sexual selection that we can encounter in plants (Grant 1995; Marshall et al. 1996){11700} In a great many species, intense competition occurs between pollen tubes, in which the individual tubes compete for the chance to fertilize the egg cell. Female plants (or the female organs of the flower) are also not completely passive in this respect (Matthys-Rochon, Gaude, & Dumas 1987; Charlesworth, Schemske, & Sork 1987). It has been found that, in some species, the female plants are capable of substantially affecting which of the pollen tubes reaches the egg cell first. It has been observed that the female plant sometimes “takes into account” the genetic diversity of the progeny (each seed in the fruit has, where possible, a different father) and at other times modifies the choice of father to the momentary external conditions (drought, damp) or its own genotype.

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The classical Darwinian theory of evolution can explain the evolution of adaptive traits only in asexual organisms. The frozen plasticity theory is much more general: It can also explain the origin and evolution of adaptive traits in both asexual and sexual organisms Read more
Draft translation from: Evoluční biologie, 2. vydání (Evolutionary biology, 2nd edition), J. Flegr, Academia Prague 2009. The translation was not done by biologist, therefore any suggestion concerning proper scientific terminology and language usage are highly welcomed. You can send your comments to flegratcesnet [dot] cz. Thank you.