Rapid evolution in crop‐weed hybrids under artificial selection for divergent life histories

Abstract

When species hybridize, offspring typically exhibit reduced fitness and maladapted phenotypes. This situation has biosafety implications regarding the unintended spread of novel transgenes, and risk assessments of crop-wild hybrids often assume that poorly adapted hybrid progeny will not evolve adaptive phenotypes. We explored the evolutionary potential of early generation hybrids using nontransgenic wild and cultivated radish (Raphanus raphanistrum, Raphanus sativus) as a model system. We imposed four generations of selection for two weedy traits – early flowering or large size – and measured responses in a common garden in Michigan, USA. Under selection for early flowering, hybrids evolved to flower as early as wild lineages, which changed little. These early-flowering hybrids also recovered wild-type pollen fertility, suggesting a genetic correlation that could accelerate the loss of crop traits when a short life cycle is advantageous. Under selection for large size at reproduction, hybrids evolved longer leaves faster than wild lineages, a potentially advantageous phenotype under longer growing seasons. Although early generation hybrid offspring have reduced fitness, our findings provide novel support for rapid adaptation in crop-wild hybrid populations. Biosafety risk assessment programs should consider the possibility of rapid evolution of weedy traits from early generations of seemingly unfit crop-wild hybrids.

Existence of vigorous lineages of crop-wild hybrids in Lettuce under field conditions

“…In plants used for the 2003 field experiments at the same site (Hooftman et al, 2005), we found a mosaic of distorted chromosomal segments, originating from both parental species, in these hybrids in the field (Orozco-ter Wengel et al, 2005). Similar genomic mixtures were found in Helianthus (Baack et al, 2008;Dechaine et al, 2009), Raphanus (Campbell et al, 2009) …”

Artificial selection on flowering time: influence on reproductive phenology across natural light environments

“…Other studies that have found strong response to selection on flowering time have often started with composite populations representing a diverse genetic pool (e.g. Campbell et al. 2009; Van Dijk 2009).…”

Contemporary evolution and the dynamics of invasion in crop–wild hybrids with heritable variation for two weedy life–histories

“…raphanistrum plants germinate slowly and inconsistently, form narrow, branching taproots and develop smaller rosette sizes before flowering early in the growing season (Panetsos and Baker ; Campbell et al. ,b).…”

“…), evolutionary responses of two key life‐history traits to directional selection (Campbell et al. ,b), and demographic analyses of populations experiencing natural selection (Campbell et al. ) to determine the influence of heritable variation for early flowering or long leaves (as an indicator of plant size) on the relative population growth of advanced‐generation hybrid and wild radish biotypes grown in a common garden in Michigan, USA.…”