Gynodioecia

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The real thyme is a gynodiac species.

Gynodiac is a form of gender distribution in flowering plants : in a population there are female plants and hermaphroditic plants (with hermaphrodite flowers).

distribution

Gynodialia is particularly common in temperate areas. For Europe, it is estimated that it is twice as common as diocese . Here it was observed in 223 species from 89 genera in 25 families . In Belgium, 7.5% of the species are gyno-dioecious. It is less common in island flora than diocyte, and in tropical forests, where diocyte is common, it is practically absent.

to form

A distinction is made between stable and unstable gyno.

Stable gynodioecia is usually determined by two non-coupled genetic factors, one is usually controlled cytoplasmic. Stable gyno is widespread within a species; the ratio of female to hermaphrodite plants is stable over time. It occurs especially in families in which diocyte is rare: mint family (Lamiaceae), daisy family (Asteraceae) and cardiac family (Dipsacaceae).

Unstable gynodioecia is controlled by a single genetic factor for male sterility that is either nuclear or cytoplasmic controlled. In the case of nuclear control, the gynodioecia can represent a preliminary stage of the diocyte. Unstable gynodialia is not very common. One reason for this is that the colonization of new locations by individual diaspores is only possible if a self-fertile hybrid emerges from it without male sterility.

genetics

Many gene loci are now known to cause male sterility. Male sterility, also called pollen sterility, is an important tool in plant breeding . The seeds of many useful plants today consist of F 1 hybrids from a male-sterile mother plant and a hermaphrodite father plant.

The Norway plantain ( Plantago lanceolata ), a gynodiac species common in Central Europe.

With cytoplasmic inheritance, all offspring of the male-sterile mother are also male-sterile. With nuclear inheritance, the mother is always heterozygous : with dominant male sterility, half of her offspring are hermaphroditic or half female. With recessive inheritance, the offspring are either half-hermaphroditic and half-female, or purely hermaphrodite, depending on whether the father is homozygous or heterozygous.

In stable gyno, it is assumed that the most common genetic variant is that of the Norway plantain ( Plantago lanceolata ): there is a cytoplasmically controlled male sterility gene (C) and two non-coupled nuclear genes (A and B), their dominant allele the sterility cancels. The following picture emerges:

  • AB- are always hermaphroditic, regardless of C
  • A-bb with C: intermediate forms with partial male fertility.
  • aaB- or aabb, with C: female

A and B overprint the activity of C. If the dominant forms of A and B are missing, plants with C are male-sterile, plants without them are hermaphroditic.

For the Norway plantain, this results in a hermaphroditic: female ratio of 15: 1 for the 16 possible combinations. However, the frequency of female plants is also density-dependent: in dense populations there is enough pollen available, so that the proportion of purely female plants is higher than in scattered populations. Between 0 and 32% female plants were counted at locations in the UK.

evolution

Gynodiopia is preferred when all-female plants are fitter mothers than hermaphrodites. The ratio of female to hermaphrodite is determined by the two factors:

  • Frequency-dependent disadvantage of purely female plants, as little pollen is available when there is a high proportion.
  • Disadvantage of the hermaphrodite mothers through self-fertilization and through the consumption of resources for pollen.

The fitness of female plants is determined by the following factors:

  • Your offspring are the result of cross-fertilization and the resulting heterosis should make them fitter.
  • Resources can be invested in fruits and seeds instead of pollen.

However, in populations that reproduce primarily through self-fertilization, gynodioecia cannot establish itself. Theoretical considerations lead to the assumption that gynodioecia mainly develops in populations that partially reproduce through self-fertilization, but the proportion of cross-fertilization is over 50%.

history

Gynodiosia was discovered by Charles Darwin and described in his book The Different Forms of Flowers on Plants of the Same Species in 1877 . Even Carl Correns dealt with it. In the later 20th century it was intensively researched in connection with plant breeding.

supporting documents

  • Adrian J. Richards: Plant Breeding Systems. 2nd edition. Chapman & Hall, London et al. 1997, ISBN 0-412-57440-3 , pp. 318-332.