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

Abstract

Gene flow in crop–wild complexes between phenotypically differentiated ancestors may transfer adaptive genetic variation that alters the fecundity and, potentially, the population growth (λ) of weeds. We created biotypes with potentially invasive traits, early flowering or long leaves, in wild radish (Raphanus raphanistrum) and F5 crop–wild hybrid (R. sativus × R. raphanistrum) backgrounds and compared them to randomly mated populations, to provide the first experimental estimate of long‐term fitness consequences of weedy life‐history variation. Using a life table response experiment design, we modeled λ of experimental, field populations in Pellston, MI, and assessed the relative success of alternative weed strategies and the contributions of individual vital rates (germination, survival, seed production) to differences in λ among experimental populations. Growth rates (λ) were most influenced by seed production, a trait altered by hybridization and selection, compared to other vital rates. More seeds were produced by wild than hybrid populations and by long‐leafed than early‐flowering lineages. Although we did not detect a biotype by selection treatment effect on lambda, lineages also exhibited contrasting germination and survival strategies. Identifying life‐history traits affecting population growth contributes to our understanding of which portions of the crop genome are most likely to introgress into weed populations.

Assessing the effects of hybridization and precipitation on invasive weed demography using strength of selection on vital rates

“…Based on our results, we predict that selection will favor loss of dormancy in crop-wild hybrid populations (i.e., selection for the crop-derived trait) and the delayed flowering that reduces the proportion of plants that survive to flower (i.e., selection against the crop-derived trait). Perhaps future demographic studies could modify the frequency of these traits within experimental populations to test whether the populations persist longer and grow faster (e.g., [4]). Alternatively, individual-based models, which characterize genotypes into groups of demographic strategies [80], could be used to compare the consequences of demographic trait variation in frequencies of possessing crop and wild traits.…”

“…To obtain the treatment matrices, we first averaged all replicates of matrices belonging to a given treatment combination (e.g., the transition frequencies of double-rain replicates 1, 2, and 3 for wild and hybrid populations were averaged) [4, 55]. We then averaged common treatment groups of these matrices to give us mean representative matrices for a given treatment (mean wild type, mean double-rain, etc.).…”

“…Hybridization between crops and their wild and weedy relatives instantaneously changes the genetic composition of weed populations [1] and thus may influence phenotypic evolution and success of weedy or invasive populations [2–4]. Crop-wild hybridization may result in either the transfer of adaptive, crop alleles to weed populations [5] or the generation of unique hybrid phenotypes via transgressive segregation [6].…”

“…Transitions among key life-history stages (e.g., rates of germination, survival and reproduction) are closely associated with individual fitness and collectively contribute to population growth, often measured as an asymptotic rate of population growth (λ) [37]. For example, fecundity strongly contributes to λ in the crop-wild Raphanus complex [4, 38]. A LTRE tests for the consequences of experimental manipulations on a population’s growth, using demographic transitions (or vital rates) as well as assessing the sensitivity of the model to proportional conversions between stages [39, 40].…”

Hybridization Slows Rate of Evolution in Crop-Wild Compared to Wild Populations of Weedy Raphanus Across a Moisture Gradient

“…These hybrid populations were particularly successful in evolving invasive traits and genetically swamping both parental populations (Hegde et al, 2006). In contrast, experimental populations of crop-wild hybrid radish are also capable of persisting for up to a decade in Michigan or Ontario (Snow et al, 2010;Shukla et al, unpublished data) but have not spread as they did in California (Snow et al, 2001;Campbell et al, 2016b;Teitel et al, 2016b). This evidence suggests that hybrid populations successfully evolve competitive weed strategies in some environments and not others, prompting us to ask how the environment influences the rate of evolution in hybrid populations relative to wild populations.…”