When divergent life histories hybridize: insights into adaptive life‐history traits in an annual weed

Abstract

Summary• Colonizing weed populations face novel selective environments, which may drive rapid shifts in life history. These shifts may be amplified when colonists are hybrids of species with divergent life histories. Selection on such phenotypically diverse hybrids may create highly fecund weeds. We measured the phenotypic variation, strength of natural selection and evolutionary response of hybrid and nonhybrid weeds.• We created F 1 hybrids of wild radish, an early flowering, small-stemmed weed, and its late-flowering, large-stemmed, crop relative (Raphanus spp.). Replicate wild and hybrid populations were established in an agricultural landscape in Michigan, USA. The consequences of three generations of natural selection were measured in a common garden experiment.• Hybrid populations experienced strong selection for larger, earlier flowering plants whereas selection was relatively weak on wild populations. Large plant size evolved two to three times faster in the hybrid populations than in wild populations, yet hybrid populations did not evolve earlier flowering. Strong selection on size and phenotypic correlations between age at reproduction and size may have limited the response of flowering phenology.• Our findings demonstrate hybridization between species with divergent life histories may catalyse the rapid evolution of certain adaptive, weedy traits while tradeoffs limit the evolution of others.

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

“…Studies of crop-wild gene fl ow also provide excellent examples of hybridization between ecologically differentiated taxa. As a consequence, these systems can be used to understand the dynamics of selection that maintain differentiation or allow for adaptive evolution ( Campbell et al, 2009 ). Yet the effects of different sources of genetic variation (nuclear vs. maternal genetic effect) on hybrid zone evolution are rarely distinguished ( Weiss et al, 2013 ) despite the fact that they can infl uence different portions of the life cycle.…”

Adaptive Differentiation in Seedling Traits in a Hybrid Pine Species Complex, Pinus densata and Its Parental Species, on the Tibetan Plateau

“…densata was supposed to be the result of niche adaption [1,5,9]. Common garden experiment in hybrid habitat is one of the most direct approaches to investigation of juvenile fitness [29].…”

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

“…Further, R. raphanistrum , with a long-lived seed bank, high genetic variability, and early emergence after soil disturbance, is considered a weed in more than 45 crop systems and 65 countries [51], so changes to its spread and persistence could impact a large diversity of agricultural cropping systems. The wild biotype, R. raphanistrum exhibits delayed germination with a long seasonal range but reaches reproductive maturity earlier than the crop biotype, R. sativus, which germinates synchronously within a few days of planting and flowers late in the season [9, 49]. These differences in key life-history traits may have important implications for the weediness of their hybrid offspring.…”

“…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]. In either case, crop-wild hybrid weed populations may exhibit significantly different phenotypes relative to ancestral wild and/or weedy populations [7–9]. The fitness advantage of these new weedy phenotypes is often context dependent [10, 11].…”

“…In fact, assessing seed production alone would have supported incorrect conclusions relative to complete life-history data in crop-wild systems of Lactuca and Raphanus , or above- and below-ground biomass of Brasica rapa and B. napus hybrids [2, 13, 36]. If crop-wild hybridization alters weed life history [e.g., [9]], these new life histories may affect vital rate contributions to population growth and alter the effectiveness of weed management practices [36]. In summary, there is little information that projects the impact of crop-wild hybridization events combined with extreme rainfall or drought events on the life-history dynamics of invasive weed populations.…”