Effects of Competition on the Fitness of Wild and Crop-Wild Hybrid Sunflower From a Diversity of Wild Populations and Crop Lines

Abstract

Abstract. Gene flow between crop fields and wild populations often results in hybrids with reduced fitness compared to their wild counterparts due to characteristics imparted by the crop genome. But the specifics of the evolutionary outcome of crop-wild gene flow may depend on context, varying due to local environmental conditions and genetic variation within and among wild populations and among crop lines. To evaluate context-dependence of fitness of F 1 hybrids, sunflower crop lines were crossed with nine wild populations from across the northern United States. These crop-wild hybrids and their wild counterparts were grown under agricultural conditions in the field with and without wheat competition. Hybrids were far less fecund than wild plants, yet more likely to survive to reproduce. There was considerable variability among wild populations for fecundity and the specific crop line used to generate the cropwild hybrid significantly affected fecundity. The fitness deficit suffered by crop-wild hybrids varied by population, as did the rankings of the crop-wild hybrids from three different crop lines. Wheat competition decreased fecundity and survival considerably and hampered seed production of wild plants more than that of hybrids. Genotype ϫ environment interactions indicated that the response of fitness to competition differed by population. Consequently, the fitness of hybrids relative to wild plants varied considerably among wild populations and was not consistent across environments. Notably, relative fitness of hybrids was greater under competitive conditions. This research is the first study of its kind to demonstrate that the consequences of crop-wild gene flow are context dependent and contingent on the genetics of the specific wild populations and the local biotic and abiotic conditions.

Roles of maternal effects and nuclear genetic composition change across the life cycle of crop–wild hybrids

“…Germination of the remaining seeds (i.e., those that that did not prematurely germinate) was high in this study, and their future survival would have been likely given the high emergence noted ( Fig. 2B, C ) and the high probability of reproduction (which was 92-100% in our study and in other studies has been >75%, e.g., Mercer et al, 2006b ). Thus, selection should act to reduce premature germination in sunfl ower crop-wild hybrid zones.…”

“…Backcrossed plants [those with 25% crop alleles and especially BC(F1)] were taller and more branched than F1 and F2 plants (50% crop alleles). Wild plant fecundity relies on extensive branching: each branch can produce one to many heads ( Snow et al, 1998 ;Mercer et al, 2006b ). The unusually large number of heads in BC(F1) plants suggests that some genetic maternal effects may remain for this trait (in addition to effects of nuclear genetic composition).…”

“…However, many seed and seedlings studies are conducted in the laboratory or greenhouse (e.g., Adler et al, 1993 ;Linder, 1998 ), or in the fi eld but having bypassed the overwintering of seeds ( Mercer et al, 2006b ;Sahoo et al, 2010 ) (but see Campbell and Waser, 2001 ;Marques et al, 2011 ). Researchers also often increase the odds of successfully establishing a fi eld experiment by watering, weeding, or applying pest control.…”

Competition alters life history and increases the relative fecundity of crop–wild radish hybrids (Raphanusspp.)

“…f In this study, the effect of competition was confounded with the effect of site since competition was imposed in the field while the without competition study was performed in a glasshouse. References: 1 Snow et al (1998), 2 Massinga et al (2005), 3 Mercer et al (2006), 4 van Gaal et al (1998, 5 Guéritaine et al (2002), 6 Pertl et al (2002), 7 Guéritaine et al (2003), 8 Hauser et al (2003), 9 Vacher et al (2004), 10 Halfhill et al (2005) under increasingly competitive conditions, the difference between hybrid and wild genotypes is often reduced by competition Uthus, 2001;Guéritaine et al, 2002;Halfhill et al, 2005;Mercer, 2005). However, in this collection of studies, imposing competition on hybrid plants rarely, if ever, reversed the relative performance of hybrids compared with their wild relative (Table 3).…”

QTL analysis reveals the genetic architecture of domestication traits in Crisphead lettuce

“…Gross and Olsen (2010) showed that there are multiple pathways to make domesticated plants and that the inferences made from genetic evidence and one cross is not always straightforward. First, QTL results can be very cultivar specific (Mercer et al 2006). The formation of a tight dense head and delay in bolting are the result of modern breeding efforts (de Vries 1997), and L. sativa 'Salinas' is one of the latest bolting and flowering ones (Simonne et al 2002).…”