Consequences of recurrent gene flow from crops to wild relatives

Abstract

Concern about gene flow from crops to wild relatives has become widespread with the increasing cultivation of transgenic crops. Possible consequences of such gene flow include genetic assimilation, wherein crop genes replace wild ones, and demographic swamping, wherein hybrids are less fertile than their wild parents, and wild populations shrink. Using mathematical models of a wild population recurrently receiving pollen from a genetically fixed crop, we find that the conditions for genetic assimilation are not stringent, and progress towards replacement can be fast, even for disfavoured crop genes. Demographic swamping and genetic drift relax the conditions for genetic assimilation and speed progress towards replacement. Genetic assimilation can involve thresholds and hysteresis, such that a small increase in immigration can lead to fixation of a disfavoured crop gene that had been maintained at a moderate frequency, even if the increase in immigration is cancelled before the gene fixes. Demographic swamping can give rise to 'migrational meltdown', such that a small increase in immigration can lead to not only fixation of a disfavoured crop gene but also drastic shrinkage of the wild population. These findings suggest that the spread of crop genes in wild populations should be monitored more closely.

Rapid spread of invasive genes into a threatened native species

“…Demographic imbalances between domestic and wild populations might create asymmetrical gene flow and deterministic spread of selectively neutral or even deleterious alleles (41). Spread can also be enhanced by differences in dispersal behavior, as in the case of Rainbow Trout and Westslope Cutthroat Trout (42), or hybrid vigor as in the case of the crayfish Orconectes rusticus and O. propinquus (39).…”

Genetic structure and relationships within and between cultivated and wild sorghum (Sorghum bicolor (L.) Moench) in Kenya as revealed by microsatellite markers

“…Moreover, information on the genetic relationships between crops and their wild/weedy relatives is useful in estimating the extent and dynamics of crop-wild gene flow. Although gene flow between crops and their relatives has been taking place since the dawn of agriculture (Ellstrand et al 1999;Haygood et al 2003), there are fears that transgenes will escape from genetically modified (GM) crops to sexually compatible wild and weedy relatives via gene flow. Depending on the relative fitness conferred by such transgenic traits in recipient wild/weedy relatives, potential harmful consequences include increased invasiveness, weediness, genetic erosion and in extreme cases extinction of populations (Ellstrand 1992;Snow and Moran-Palma 1997;Bhatia and Mitra 2003;Conner et al 2003;Haygood et al 2003;Cleveland and Soleri 2005;Thies and Devare 2007;Auer 2008;Chandler and Dunwell 2008).…”

SSR markers to detect gene flow from upland to mocó cotton

“…Gene flow from crops to local varieties may just increase slightly the variability in the target population, or otherwise it may harm population conservation, especially if genes or genomes hybridization increases or decreases adaptability or reproduction taxes. Hybrid fitness higher than the fitness of both parents may lead to progenitor extinction by replacement (HEDGE et al, 2006), while if hybrids are less fertile than parents, populations may shrink (HAYGOOD et al, 2003). Paternity analysis may provide accurate information about gene flow (NEFF et al, 2000).…”