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

Abstract

BackgroundAs global climate change transforms average temperature and rainfall, species distributions may meet, increasing the potential for hybridization and altering individual fitness and population growth. Altered rainfall specifically may shift the strength and direction of selection, also manipulating population trajectories. Here, we investigated the role of interspecific hybridization and selection imposed by rainfall on the evolution of weedy life-history in non-hybrid (Raphanus raphanistrum) and hybrid (R. raphanistrum x R. sativus) populations using a life table response experiment.ResultsIn documenting long-term population dynamics, we determined intrinsic (r) and asymptotic (λ) population growth rates and sensitivities, a measure of selection imposed on demographic rates. Hybrid populations experienced 8.7-10.3 times stronger selection than wild populations for increased seedling survival. Whereas crop populations generally exhibit little dormancy and wild populations often exhibit dormancy, non-hybrid populations experienced 10% stronger selection than hybrid populations for exhibiting seed dormancy. Selection on survival-to-flowering in wild, not hybrid, populations declined marginally with increasing soil moisture. Hybrid populations exhibited greater r, but not λ, than wild populations regardless of moisture environment. In general, fecundity contributed most to differences in λ but fecundity only contributed positively to hybrid λ relative to wild λ when precipitation was altered (either higher or lower than control) and not under control watering conditions.ConclusionsSelection on key demographic traits may not change dramatically in response to rainfall, and hybridization may more strongly influence the demography of these weedy species than rainfall. If hybrid populations can respond to selection for increased dormancy, this may make it more difficult to deplete weed seed banks and increase the persistence of crop genes in weed populations.

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

“…Fifth generation plants were transplanted and grown in 2015 and 2016 common gardens at KSR. may have experienced genetic drift (Teitel et al, 2016a). However, the experimental design used allowed us to detect the consequences of genetic drift-if there was substantial genetic drift, we predicted there would be significant differentiation among the five replicate lineages, within experimental treatment combinations; which we did not find (Shukla et al, unpublished data).…”

“…Research addressing the influence of the environment on the spread of crop-wild hybrid weeds is an important, preventative step in managing the risk of the evolution of crop-wild hybrid weeds. Our work evaluates the effect of watering on the rate of evolution of crop-wild hybrid weeds and, although our results suggest watering does not drive weedy trait evolution in crop-wild hybrids, it raises new questions on what facilitates the rate of evolution and success of hybrid radish documented in other environments (Campbell et al, 2006;Hegde et al, 2006;Campbell and Snow, 2007;Hovick et al, 2012;Teitel et al, 2016a). Although, research evaluating environmental variation on invasive potential can take time to properly test and evaluate, thorough research can be critical in creating and implementing effective IWM and policy.…”

“…Plots were ∼200 meters apart to minimize gene flow among plots; although likely negligible, some gene-flow may have occurred. In the F 0 generation, gene-flow naturally occurred within mixed plots of wild and cultivatedcrop plants and gave rise to the first generation (i.e., F 1 ) of wild and crop-wild hybrid (R. sativus × R. raphanistrum) seeds (Teitel et al, 2016a). As previously described (e.g., Campbell et al, 2016a;Teitel et al, 2016a), we manipulated soil moisture using rainout shelters and imposed one of four watering treatments within these plots/shelters to impose a natural selection experiment on replicated wild and crop-wild hybrid radish populations:…”

“…The relative success of crop-wild hybrid populations have varied across North America-from highly successful in California and Texas (Hegde et al, 2006;Hovick et al, 2012) to moderately successful in Michigan, USA and Ontario, Canada (Campbell et al, 2006;Campbell and Snow, 2007;Teitel et al, 2016a). Along with differences in soil moisture, one of the most apparent differences among these studies is temperature and length of growing season.…”

Growth and fecundity of colonizing hybrid Raphanus populations are environmentally dependent

“…When introduced into a novel environment (Texas), hybrid populations again outperformed wild populations (Hovick et al, 2012). In Michigan and Ontario, populations of hybrids were, at varying times, either less, equally, or more fecund than wild populations (Campbell et al, 2006; Campbell and Snow, 2007; Teitel et al, 2016b). Hybrid radish populations vary in the strength of selection they experience on phenological traits across locations that differ in water availability (Campbell et al, 2009a, 2014; Hovick et al, 2012).…”