In plant biology, Vavilovian mimicry (also crop mimicry or weed mimicry) is a form of mimicry in plants where a weed evolves to share one or more characteristics with a domesticated plant through generations of artificial selection. It is named after Nikolai Vavilov, a prominent Russian plant geneticist. 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 selection by humans. Although the human selective agents might be conscious of their impact on the local weed gene pool, such effects go against the goals of those growing crops. Weeders do not want to select for weeds that are increasingly similar to the cultivated plant, yet the only other option is to let the weeds grow and compete with crops for sunlight and nutrients. Similar situations include antibiotic resistance and, also in agricultural crops, 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, aggressive (parasitic) and, in the case of secondary crops, mutualistic. It is a form of disjunct mimicry with the model agreeable to the dupe. In disjunct mimicry complexes, three different species are involved as model, mimic and dupe—the weed, mimicking a protected crop model, with humans as signal receivers (dupe). Vavilovian mimicry bears considerable similarity to Batesian mimicry (where a harmless organism mimics a harmful species) in that the weed does not share the properties that give the model its protection, and both the model and the dupe (in this case humans) are negatively affected by it. There are some key differences, though; in Batesian mimicry the model and signal receiver are enemies (the 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. On this first point, Georges Pasteur points out that "indirect artificial selection" is involuntary and thus no different from natural selection. 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
One case of Vavilovian mimicry is the gold-of-pleasure or false flax (Camelina sativa linicola), which looks much like the flax plant Linum usitatissimum, and occurs with it in the field. The gold-of-pleasure is a descendant of Camelina gabrata, a wild species; its subspecific name linicola means "the one that lives with flax". Weeding of the adult plant is impractical; instead they are separated based on properties of the seed. This is done by a 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.