Abstract
Background and Aims Gene flow from crops to their wild relatives has the potential to alter population growth rates and demography of hybrid populations, especially when a new crop has been genetically modified (GM). This study introduces a comprehensive approach to assess this potential for altered population fitness, and uses a combination of demographic data in two habitat types and mathematical (matrix) models that include crop rotations and outcrossing between parental species.Methods Full life-cycle demographic rates, including seed bank survival, of non-GM Brassica rapa × B. napus F1 hybrids and their parent species were estimated from experiments in both agricultural and semi-natural habitats. Altered fitness potential was modelled using periodic matrices including crop rotations and outcrossing between parent species.Key Results The demographic vital rates (i.e. for major stage transitions) of the hybrid population were intermediate between or lower than both parental species. The population growth rate (λ) of hybrids indicated decreases in both habitat types, and in a semi-natural habitat hybrids became extinct at two sites. Elasticity analyses indicated that seed bank survival was the greatest contributor to λ. In agricultural habitats, hybrid populations were projected to decline, but with persistence times up to 20 years. The seed bank survival rate was the main driver determining persistence. It was found that λ of the hybrids was largely determined by parental seed bank survival and subsequent replenishment of the hybrid population through outcrossing of B. rapa with B. napus.Conclusions Hybrid persistence was found to be highly dependent on the seed bank, suggesting that targeting hybrid seed survival could be an important management option in controlling hybrid persistence. For local risk mitigation, an increased focus on the wild parent is suggested. Management actions, such as control of B. rapa, could indirectly reduce hybrid populations by blocking hybrid replenishment.
Highlights
Gene flow and hybridization between crops and their wild relatives is common and has been so since the beginning of agriculture (Ellstrand, 2003)
In all semi-natural habitats, most B. napus (OSR) plants did not persist beyond the vegetative phase, with only seven plants flowering and none producing pods out of the 2250 B. napus seeds sown (Table 1); no full life-cycle characteristics can be given and k is 0
In this study we assessed which aspects of the life cycle of hybrids and their parents were of principal importance for the persistence of hybrids
Summary
Gene flow and hybridization between crops and their wild relatives is common and has been so since the beginning of agriculture (Ellstrand, 2003). In the case of planting of genetically modified (GM) crops this incorporation of (trans) genes into wild relatives is generally considered as undesirable (Chandler and Dunwell, 2008; Schierenbeck and Ellstrand, 2009) and has been found in several cases (Ellstrand et al, 2010) This includes the occurrence of transgenic hybrids among Brassica species (Warwick et al, 2008). Gene flow between crops and wild relatives does not per se constitute a risk to the environment, but could alter the dynamics of plant populations, changing their population growth rates (‘fitness’) and persistence both inside and outside an agricultural environment Such increased fitness might lead to environmentally damaging changes in agricultural management with regard to herbicide use and weeding practices (Hawes et al, 2003), or changes in overall structure and function of ecosystems (Chandler and Dunwell, 2008; Kwit et al, 2011). Altered fitness potential was modelled using periodic matrices including crop rotations and outcrossing between parent species
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