Vavilovian mimicry

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The gold-of-pleasure or false flax on the left (denoted by number 1) resembles flax and its seeds are practically inseparable from the flax seed.

In plant biology, Vavilovian mimicry (also crop mimicry or weed mimicry

artificial selection.[2] It is named after Nikolai Vavilov, a prominent Russian plant geneticist.[2] Selection against the weed may occur by killing a young or adult weed, separating its seeds from those of the crop (winnowing), or both. This has been done manually since Neolithic times, and in more recent years by agricultural machinery
.

Vavilovian mimicry is a good illustration of unintentional

herbicide resistance
. Having acquired many desirable qualities by being subjected to similar selective pressures, Vavilovian mimics may eventually be domesticated themselves. Vavilov called these weeds-become-crops secondary crops.

Classification and comparisons

Vavilovian mimicry can be classified as reproductive,

predator would eat the protected species if it could), whereas here the crop and its human growers are in a mutualistic
relationship: the crop benefits from being dispersed and protected by people, despite being eaten by them. In fact, the crop's only 'protection' relevant here is its usefulness to humans. Secondly, the weed is not eaten, but simply killed (either directly or by not planting the seed). The only motivation for killing the weed is its effect on crop yields. Farmers would prefer to have no weeds at all, but a predator would die if it had no prey to eat, even if they might be difficult to identify. Finally, there is no known equivalent of Vavilovian mimicry in ecosystems unaltered by humans.

Delbert Wiens has argued that secondary crops cannot be classified as mimics, because they result from artificial as opposed to natural selection, and because the selective agent is a machine.[3] On this first point, Georges Pasteur points out that "indirect artificial selection" is involuntary and thus no different from natural selection.[2] That the signal receiver is an inanimate object certainly deviates from the normal case of a dupe perceiving the signal, but the result is no different from that of manual selection that has been occurring since the Neolithic Revolution.

Examples

Rye is a secondary crop, originally being a mimetic weed of wheat.

One case of Vavilovian mimicry is the

winnowing machine
, which in this case acts as an inanimate signal receiver. Seeds that are thrown the same distance as flax seeds have thus been selected for, making it near impossible to separate the seeds of these two species.

Though now an important crop, oats were once just another weed.

Another example is

tilled. However, there are occasional mutants that do set seed. These have been protected from destruction, and rye has thus evolved to become an annual plant.[5]

Rye is a hardier plant than wheat, surviving in harsher conditions. Having become

preadapted as a crop through wheat mimicry, rye was then positioned to become a cultivated plant in areas where soil and climatic conditions favored its production, such as mountainous terrain.[4]

This fate is shared by

oats (Avena sativa and Avena byzantina), which also tolerate poorer conditions, and like rye, grow as a weed alongside wheat and barley. Derived from a wild species (Avena sterilis), it has thus come to be a crop in its own right. Once again paralleling wheat, rye and other cereals, oats have developed tough spindles which prevent seeds from easily dropping off, and other characteristics which also help in natural dispersal have become vestigial, including the awns which allow them to self bury.[4]

The flax-dodder (Cuscuta epilinum) is a creeper that grows around flax and linseed plants. Much like the other cases, its seeds have become larger. A mutant double-seeded variety has become prevalent, as seed size has once again been the character upon which selection has acted.[4]

Selection can also occur on the vegetative stage, through hand weeding. Weeding often takes place when the crop plant is very young, and most vulnerable. Echinochloa oryzoides, a species of grass which is found as a weed in rice (Oryza sativa) fields, looks similar to rice and its seeds are often mixed in rice and difficult to separate. This close similarity was enhanced by the weeding process which is a selective force that increases the similarity of the weed in each subsequent generation.[6]

See also

Notes

  1. ^ In this case the weed is the mimic, not the model as in ant mimicry.

References

  1. ^ Maran, Timo. "Mimicry". In Bouissac, Paul; Lewis, Ann; Lynch, Alejandro (eds.). Semiotics Encyclopedia Online. E. J. Pratt Library, Victoria College, University of Toronto. Retrieved 2007-10-19.
  2. ^
    doi:10.1146/annurev.es.13.110182.001125
    .
  3. ^ Wiens, D. (1978). "Mimicry in plants". Evolutionary Biology. 11: 365–403.
  4. ^
    ISBN 0-07-070100-8
    .
  5. S2CID 86549764
    .
  6. ^ Barrett, S. (1983). "Mimicry in Plants". Scientific American. No. 257. pp. 76–83.

Sources

Further reading
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