Rapid establishment of a flowering cline in Medicago polymorpha after invasion of North America

Abstract

To establish and spread in a new location, an invasive species must be able to carry out its life cycle in novel environmental conditions. A key trait underlying fitness is the shift from vegetative to reproductive growth through floral development. In this study, we used a common garden experiment and genotyping‐by‐sequencing to test whether the latitudinal flowering cline of the North American invasive plant Medicago polymorpha was translocated from its European native range through multiple introductions, or whether the cline rapidly established due to evolution following a genetic bottleneck. Analysis of flowering time in 736 common garden plants showed a latitudinal flowering time cline in both the native and invaded ranges where genotypes from lower latitudes flowered earlier. Genotyping‐by‐sequencing of 9,658 SNPs in 446 individuals revealed two major subpopulations of M. polymorpha in the native range, only one of which is present in the invaded range. Additionally, native range populations have higher genetic diversity than invaded range populations, suggesting that a genetic bottleneck occurred during invasion. All invaded range individuals are closely related to plants collected from native range populations in Portugal and southern Spain, and population assignment tests assigned invaded range individuals to this same narrow source region. Taken together, our results suggest that latitudinal clinal variation in flowering time has rapidly evolved across the invaded range despite a genetic bottleneck following introduction.

Diversity of Naturalized Hairy Vetch (Vicia villosa Roth) Populations in Central Argentina as a Source of Potential Adaptive Traits for Breeding

“…Observed large variability within available germplasm could be used by breeders to select parental accessions for HV improvement breeding program that maximizes the winterspring biomass with low PY for cover crops (Wilke and Snapp, 2008;Wayman et al, 2016), or with high PY for´ley farmingś ystems (Loi et al, 2005;Renzi et al, 2017;Renzi et al, 2018). No significant correspondence was found between the geographic distance matrix and the phenotypic distance matrix (P > 0.15) among the naturalized AR populations and these results differ from Medicago polymorpha L., in which a correspondence between collection site and phenotypic traits (Loi et al, 1993;Helliwell et al, 2018) was observed.…”

Adaptation to climate change through genetic accommodation and assimilation of plastic phenotypes

“…It is also common for populations of temperate plants and ectotherms along latitudinal and altitudinal gradients to vary in responses to phenological cues [60], with strong selection on loci contributing to divergence in phenological timing [61] and rapid establishment of latitudinal clines in phenology in introduced species [62]. A recent common garden experiment transplanted replicate genotypes of the riparian tree Poplus fremontii across 58 of latitude, demonstrating that populations varied in their phenological plasticity and had substantial within-population G Â E [63].…”

Rapid evolution of Medicago polymorpha during invasion shifts interactions with the soybean looper

“…Any of these processes would yield a pattern similar to enemy release but achieved through evolutionary processes. Our results suggest that novel genotypes, particularly those from regions above southern Portugal (Helliwell et al, 2018), attempting to colonize would have their establishment hampered compared to already present M. polymorpha. We did not compare herbivory in wild populations under natural field conditions and thus are not making inferences about the impact of herbivory on traits in each range.…”

“…This hierarchical sampling accounts for range, between-population, and within-population genetic variation and is captured in the mixed models we used for analysis. The study by Helliwell et al (2018) based on a novel, expanded collection that was not available to us showed that M. polymorpha variation is highest at the population level and lowest at the range level and found evidence supporting rapid evolution for flowering time in the invaded region. Future work leveraging genetic and genomic tools could partition how much of the change in plant-herbivore interactions is due to adaptation through natural selection versus genetic drift (Agrawal et al, 2015;Keller & Taylor, 2008;Schrieber et al, 2017).…”