Glucosinolates promote initial population establishment of feral oilseed rape

Abstract

Background. Crops are often selected for traits that confer a selective disadvantage in the wild. A key trait that has been greatly altered by domestication is investment in herbivore defence. It remains unclear, however, whether variation in chemical defence affects a crop's ability to colonize semi-natural habitats where it typically has to compete with a resident community. Here, we investigate how breeding efforts aimed at reducing glucosinolate levels in seeds -canonical herbivore deterrents -influence initial establishment of Brassica populations spanning a wild-feral-domesticated gradient. Methods. We followed the dynamics of twenty-nineBrassica accessions in two experimental fields by recording life table parameters and vegetation cover biannually over a two-year period. Accessions were selected to vary in their glucosinolate content, and included lines of wild turnip (B. rapa), feral B. napus as well as modern canola and historical oilseed rape cultivars. Populations were established by sowing seeds on bare soil after which the natural vegetation was allowed to regenerate, providing a temporal gradient in the degree of interspecific competition.Results. Populations flourished in the first year, but many perished during a second year of growth, in particular those of oilseed rape. Declines coincided with an increase in vegetation cover, but were slower in populations harbouring more glucosinolates. These compounds had opposing effects on different life cycle stages: seedling establishment was greater in highglucosinolate lines, which traded off with reduced post-recruitment survival. Crucially, the effect of glucosinolates on persistence was lost when focussing on oilseed rape only, but the underlying demographic trade-off remained.Discussion. Our study illustrates that initial establishment of feral oilseed rape is governed by glucosinolate-mediated trade-offs between seedling recruitment and subsequent survival, with low-glucosinolate lines (modern canola) being most successful when post-recruitment conditions are relatively benign. Such demographic trade-offs likely extend to other species, and must be considered when managing escaped crops and invasive plants.