POLLINATOR PREFERENCES AND THE PERSISTENCE OF CROP GENES IN WILD RADISH POPULATIONS (RAPHANUS-RAPHANISTRUM, BRASSICACEAE)

Crop-weed hybridization can potentially influence the evolutionary eco logy of wild populations. Many crops are known to hybridize with wild relatives, but few studies have looked at the long-term persistence of crop genes in the wild. This study investigated one factor in the hyb ridization process in radish: differential pollinator visitation to wi ld radish (Raphanus raphanistrum) vs. crop-wild F-1 hybrids (R. sativu s X R. raphanistrum). Wild genotypes had yellow flowers, a recessive s ingle-locus trail, whereas hybrids always had white or pale pink flowe rs. In experimental arrays in northern Michigan, total pollinator visi tation was significantly biased toward wild plants when the frequencie s of wild and hybrid plants were equal. Syrphid flies, the most freque nt visitors, preferred wild plants while bumble bees showed no prefere nce. This pattern was also observed when hybrid plants were overrepres ented in the array (12 hybrid:2 wild). In contrast, when hybrid plants were rare (2 hybrid:12 wild), neither morph was preferred by any poll inator group. Later in the summer, pollinators were also observed in a large experimental garden with nearly equal frequencies of wild and h ybrid plants. Cabbage butterflies (Pieris rapae) strongly overvisited wild plants, while bumble bees showed a slight preference for hybrids. Taken together, these studies suggest that F-1 hybrids may not be at a disadvantage with regard to pollinator visits when they occur at low frequencies or when bumble bees are frequent flower visitors. Thus, v ariation in the proportion of white-flowered morphs among wild radish populations could be influenced by different histories of crop-to-wild hybridization, as well as by variation in the composition of local po llinator taxa.