Phenotypic selection under two contrasting environments in wild sunflower and its crop–wild hybrid

Abstract

Hybridization is a common phenomenon in plants and can lead to the introgression of alleles from one population into another, generate new hybrid lineages, or cause species extinction. The environmental conditions and the genetic background of the participating populations may influence these outcomes since they can affect the fitness of hybrids, thereby increasing or decreasing the chances of introgression. Thus, it is important to understand the context‐dependent prospects for introgression of alleles into diverse populations and under multiple ecological environments. Crop–wild hybridization presents an opportunity to explore these dynamics in agroecosystems. To this end, we used diverse wild and hybrid sunflowers from across the northern United States as a basis for evaluating variation in morphological traits and assessing context‐dependent selection. These crop–wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Interactions between origin and cross type affected expression of early functional traits, while interactions between competition and cross type acted on reproductive traits. A smattering of early and reproductive traits was affected by interactions between cross type and competition that varied by origin (i.e., 3‐way interactions). Seven functional traits, especially number of branches and tertiary head diameter, underwent net and direct directional selection, while six out of these seven traits appear to also be experiencing nonlinear selection dynamics. In general, wild‐like traits were favored under both sets of conditions, while, under wheat competition, some crop‐like traits related to fast growth and primary head diameter became important. These data reaffirm the hypothesis that stressful conditions establish a scenario more suitable for crop introgression and clarify that nonlinear selection dynamics may play a role in this process.

Rapid evolution of seed dormancy during sunflower de-domestication

“…This indicates that crop-wild hybridization is not required but it may facilitate the ecological transition from ruderal to agricultural habitats. Recently, we showed that wild-like traits are under selection in both ruderal and agricultural habitats, but selection is generally weaker in the latter (Presotto et al, 2019). A weaker selection for wild-like traits can explain why crop-wild hybrids are (apparently) more successful away from hybrid zones.…”

“…In sunflower, no major genes of large effect have been identified for seed dormancy but many small-effect QTLs (Brunick, 2007; Gandhi et al, 2005), making the evolution of seed dormancy through new mutations in multiple regions very unlikely. Hybridization between wild and cultivated sunflowers leads to high phenotypic and genetic variation on which selection can act (Muller et al, 2011; Presotto et al, 2019). After hybridization, wild and cultivated alleles starting at high frequencies and novel recombinations may produce transgresive phenotypes (Rieseberg et al, 2003).…”

“…However, both BRW 07 and BRW 17 grew faster than BAR, suggesting that traits related to rapid growth were already present in the biotypes collected in 2007. Cultivated and wild sunflower largely differ in early growth (Hernández et al, 2020; Kost et al, 2015; Mercer et al, 2007), and phenotypic selection analyses suggest that an early rapid growth is advantageous in agricultural environments, therefore, it is expected to be selected rapidly (Kost et al, 2015; Presotto et al, 2019). In previous studies using BRW 07 , we showed that early rapid growth has probably evolved at the expense of lower stress tolerance in this biotype (Casquero and Cantamutto, 2016; Presotto et al, 2017), a similar pattern to that observed in North American weedy biotypes (Mayrose et al, 2011).…”

“…In Argentina, several hybrid zones were formed where wild and cultivated sunflower often grow in sympatry (Ureta et al, 2008), however, to our knowledge, no biotypes have invaded agricultural fields in these zones (Mondon et al, 2018). Despite the frequent occurrence of natural crop-wild hybrids in these areas (Mondon et al, 2018; Ureta et al, 2008), no evidence of permanent crop introgression was found (Mondon et al, 2018), probably due to ecological barriers for crop to wild introgression (Mercer et al, 2007; Presotto et al, 2019).…”

Compensation of Wild Plants Weakens the Effects of Crop-Wild Gene Flow on Wild Rice Populations

“…A similar pattern was also detected in sunflower (Mercer et al, 2007 ), lettuce (Hartman et al, 2012 ), radish (Hegde et al, 2006 , Snow et al, 2009 ), and rape (Rose et al, 2009 ). Together, these findings suggest that some domestication traits and genome segments originating from crops may maintain and enhance crop-wild hybrid fitness (Mercer et al, 2007 ; Corbi et al, 2017 ; Presotto et al, 2019 ), although crop traits are expected to reduce fitness in wild populations (Stewart et al, 2003 ; Hails and Morley, 2005 ).…”