How big a risk are cultivars to their wild progenitors?

Nature Talk
#1

The California poppy is a beloved flower, and the state flower of California, but as this thread discussed, the cultivated forms are thought to interbreed with wild populations, potentially wiping out their local genetic adaptations.

What was not discussed in that thread was that, whereas the wild-type California poppy consistently has orange or yellow-orange flowers, there are cultivars with flower colors ranging from white to salmon and even purple. If such cultivars are grown within the wild-type’s native range, one would expect – if interbreeding is a real risk – to see those cultivar colors beginning to show up in wild populations, at least in the F2 generation.

Let’s expand it beyond the poppies, but keep it limited to same-species cultivars vs wild-type, i.e. leaving aside the related issue of interspecific hybridization. How prevalent are documented cases of this kind of genetic “contamination”? Do we see wild populations taking on the visible phenotypes of same-species cultivars grown in their range?

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#2

I don’t really study this type of thing or have any data to reference, but I think that because so many cultivars are created by humans selecting for mutations/genes that don’t persist naturally, there likely isn’t too much risk in general. No doubt, there are instances where the opposite could be true. Even in wild populations of organisms, there can be ‘off’ colors (or whatever characteristic), but those don’t typically persist for one reason or another. Maybe they don’t attract pollinators, maybe they make the organism an easier target for predators, etc., but if the wild-type characteristic is consistent, it seems that it would be that way for a reason.

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#3

I agree. This is a subject that has been debated since Charles Darwin’s time.

And we have seen in the chapter on the Struggle for Existence that it is the most closely-allied forms, — varieties of the same species, and species of the same genus or of related genera, — which, from having nearly the same structure, constitution, and habits, generally come into the severest competition with each other. Consequently, each new variety or species, during the progress of its formation, will generally press hardest on its nearest kindred, and tend to exterminate them.

From On the Origin of Species by Charles Darwin, 1st Edition, 1859, Chapter IV, pp. 110 (130), lines 24-33.

#4

The mutant traits would need to confer a reproductive advantage for them to increase in frequency in the wild population (natural selection). An adaptive trait can only be replaced with a better adaptive trait (unless the wild population was small relative to the cultivar population in which case the role of chance could overpower the role of selection in increasing the frequency of a maladaptive trait (genetic drift). However, many cultivars are the product of hybridization with other species–so genes could leak out into the wild population by that route. But again, only if they conferred a reproductive advantage or the wild population was small relative to the cultivar population.

Here’s a paper that explores this question in a flower seeded along highways all over Texas.
https://doi.org/10.1093/jhered/esx094

A related issue that is being discussed is where to source seed for restoration projects. This article is behind a paywall, but the abstract is available.
https://doi.org/10.1016/j.baae.2009.09.002

I suspect the main risk is the continued planting of a cultivar of a species that is native to an area (propagule pressure) which would cause genetic homogenization among the native strains which almost always show some degree of uniqueness among local populations. Genetic homogenization, then, reduces the future evolutionary potential of the species.

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#5

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