Can wild relatives survive introgression?

Crops can benefit from the introgression of genes from their wild relatives, but what about the other way around? Is the survival of crop wild relatives jeopardized by the “genetic pollution” caused by hybridization with the cultigen? A paper just out in the Journal of Applied Biology takes an experimental and modeling approach to answering this question ((D. A. P. Hooftman, M. J. De Jong, J. G. B. Oostermejer, H. C. M. Den Nijs. 2007. Modelling the long-term consequences of crop-wild relative hybridization: a case study using four generations of hybrids. Journal of Applied Ecology 44 (5), 1035–1045.)).

The researchers monitored the germination, survival and seed-set of hybrids between wild (Lactuca serriola) and cultivated lettuce (L. sativa). The overall fitness of hybrids was higher than that of the “unpolluted” wild relative in the first couple of generations, but as those hybrids were selfed and backcrossed, their fitness decreased. These data were then entered into a model, to see what would happen over time to a L. serriola population exposed to geneflow from the cultigen. What happens is that the wild relative can indeed be completely displaced by hybrids, but that is not a foregone conclusion, and in any case displacement, if it takes place, will not be as rapid as predicted by previous models which did not take into account the breakdown in heterosis.

So genetic pollution does pose a real threat to crop wild relatives in the field ((The likelihoods of both hybrid occurrence and L. serriola displacement were still at least 60%.)), but perhaps not as great as some have suggested. And in any case we now seem to have a model that can be used to assess the risk of genetic pollution, including by transgenes.