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Premise of the Study: Novel nuclear microsatellite markers were developed for the invasive plant Oplismenus undulatifolius (Poaceae) to facilitate studies of invasion dynamics for this recently introduced, high‐risk invasive species in North American mid‐Atlantic forests. Methods and Results: Sixteen polymorphic microsatellite loci were isolated and characterized from an Illumina paired‐end shotgun library of O. undulatifolius after initial assessment of 48 loci. When screened in three populations, these markers identified two to six alleles per locus. Observed heterozygosity ranged from 0.000 to 1.000. All loci were successfully amplified in the North American native congener O. hirtellus. Conclusions: We provide the first nuclear genetic resources available for population genetic studies within the genus Oplismenus. These markers will serve as a critical tool for exploring patterns of gene flow and mechanisms of invasion of O. undulatifolius across its introduced range. These microsatellites should also be suitable for studies in other Oplismenus species. [ABSTRACT FROM AUTHOR]

A long-standing question in evolutionary biology asks whether the genetic changes contributing to phenotypic evolution are predictable. Here, we identify a genetic change associated with segregating variation in flower color within a population of Mimulus lewisii. To determine whether these types of changes are predictable, we combined this information with data from other species to investigate whether the spectrum of mutations affecting flower color transitions differs based on the evolutionary time-scale since divergence. We used classic genetic techniques, along with gene expression and population genetic approaches, to identify the putative, loss-of-function mutation that generates rare, white flowers instead of the common, pink color in M. lewisii. We found that a frameshift mutation in an anthocyanin pathway gene is responsible for the white-flowered polymorphism found in this population of M. lewisii. Comparison of our results with data from other species reveals a broader spectrum of flower color mutations segregating within populations relative to those that fix between populations. These results suggest that the genetic basis of fixed differences in flower color may be predictable, but that for segregating variation is not. [ABSTRACT FROM AUTHOR]

Premise of the study: Novel microsatellite primers were developed for the native wildflower Ipomopsis aggregata to facilitate ongoing studies of the genetics of local adaptation and patterns of hybridization with closely related species within the genus. Methods and Results: Thirteen primer sets were successfully developed and tested using populations from the Rocky Mountains of Colorado, USA. The primers amplified di-, tri-, and tetranucleotide repeats with 1-15 alleles per locus. All primers also amplified fragments with varying success in closely related Ipomopsis species and more distant members of the Polemoniaceae. Conclusions: The polymorphism levels observed across all loci suggest that these microsatellites may be useful for population genetic studies in Ipomopsis , as well as in studies of other related taxa in the Polemoniaceae. [ABSTRACT FROM AUTHOR]

Speciation is characterized by the evolution of reproductive isolation between two groups of organisms. Understanding the process of speciation requires the quantification of barriers to reproductive isolation, dissection of the genetic mechanisms that contribute to those barriers and determination of the forces driving the evolution of those barriers. Through a comprehensive analysis involving 19 pairs of plant taxa, we assessed the strength and patterns of asymmetry of multiple prezygotic and postzygotic reproductive isolating barriers. We then reviewed contemporary knowledge of the genetic architecture of reproductive isolation and the relative role of chromosomal and genic factors in intrinsic postzygotic isolation. On average, we found that prezygotic isolation is approximately twice as strong as postzygotic isolation, and that postmating barriers are approximately three times more asymmetrical in their action than premating barriers. Barriers involve a variable number of loci, and chromosomal rearrangements may have a limited direct role in reproductive isolation in plants. Future research should aim to understand the relationship between particular genetic loci and the magnitude of their effect on reproductive isolation in nature, the geographical scale at which plant speciation occurs, and the role of different evolutionary forces in the speciation process.

Spatial variation in natural selection may play an important role in determining the genetic structure of hybridizing populations. Previous studies have found that F1 hybrids between naturally hybridizing Ipomopsis aggregata and Ipomopsis tenuituba in central Colorado differ in fitness depending on both genotype and environment: hybrids had higher survival when I. aggregata was the maternal parent, except in the centre of the hybrid zone where both hybrid types had high survival. Here, we developed both maternally (cpDNA PCR-RFLP) and biparentally inherited (nuclear AFLP) species-diagnostic markers to characterize the spatial genetic structure of the natural Ipomopsis hybrid zone, and tested the prediction that the majority of natural hybrids have I. aggregata cytoplasm, except in areas near the centre of the hybrid zone. Analyses of 352 individuals from across the hybrid zone indicate that cytoplasmic gene flow is bidirectional, but contrary to expectation, most plants in the hybrid zone have I. tenuituba cytoplasm. This cytotype distribution is consistent with a hybrid zone in historical transition, with I. aggregata nuclear genes advancing into the contact zone. Further, nuclear data show a much more gradual cline than cpDNA markers that is consistent with morphological patterns across the hybrid populations. A mixture of environment- and pollinator-mediated selection may contribute to the current genetic structure of this hybrid system.