hybridization
Ridley CE & Ellstrand NC 2010 Rapid evolution of morphology and adaptive life history in the invasive California wild radish (Raphanus sativus) and the implications for management. Evol Appl 3:64-76.
- early generation Raphanus hybrids quickly respond to ecologically relevant artificial selection
- in some cases, even faster than pure parental lineages
- the progenitor parents R. sativus (cultivated radish) and the related weed R. raphanistrum ... hybridized to create a stable lineage now known as California wild radish
- California wild radish displays high amounts of neutral genetic variation, likely because of both extensive inter-specific hybridization and multiple introductions
- Panetsos and Baker proposed that crop-like populations with a higher frequency of crop traits such as purple and white flowers and swollen roots existed closer to the coast because of suitability to moist, mild environments
- Raphanistrum-like populations with a higher frequency of traits like yellow flowers and tough, penetrating taproots, on the other hand, existed in the inland valleys because they were better adapted to harsher, dry conditions
- the adaptive argument for phenotypic divergence was never explicitly tested against a null, nonadaptive explanation that could account for the differences between invasive populations
- it is possible and even likely that contrasting introduction histories and/or levels of hybridization have caused invasive populations to diverge in ways that are not adaptive
