Evolution of multiple postzygotic barriers between species of the Mimulus tilingii complex.

Species are often defined by their ability to interbreed (i.e., Biological Species Concept), but determining how and why reproductive isolation arises between new species can be challenging.

Characterization of polymorphic microsatellite loci for invasive wavyleaf basketgrass, (Poaceae).

Premise Of The Study: Novel nuclear microsatellite markers were developed for the invasive plant (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 after initial assessment of 48 loci. When screened in three populations, these markers identified two to six alleles per locus.

Evidence for natural hybridization between native and introduced lineages of Phragmites australis in the Chesapeake Bay watershed.

Premise Of The Study: The introduction of nonnative taxa into areas occupied by conspecifics can lead to local extinction of native taxa via habitat modification and competitive dominance, and be exacerbated by outbreeding depression or the formation of invasive hybrid lineages following intraspecific gene flow. The expansion of Eurasian Phragmites australis into tidal wetlands of North America has been accompanied by a dramatic decline of native P. australis, with few relic populations remaining along the Atlantic coastline of the United States, particularly in the Virginia portion of the Chesapeake Bay.

The genetic basis of a rare flower color polymorphism in Mimulus lewisii provides insight into the repeatability of evolution.

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.

Microsatellite loci in Ipomopsis aggregata (Polemoniaceae) and cross-species applicability for ecological genetics studies.

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.

Photosynthetic and growth responses of reciprocal hybrids to variation in water and nitrogen availability.

Premise Of The Study: Fitness of plant hybrids often depends upon the environment, but physiological mechanisms underlying the differential responses to habitat are poorly understood. We examined physiological responses of Ipomopsis species and hybrids, including reciprocal F(1)s and F(2)s, to variation in soil moisture and nitrogen. •

Methods: To examine responses to moisture, we subjected plants to a dry-down experiment.

Natural variation for drought-response traits in the Mimulus guttatus species complex.

Soil moisture is a key factor affecting plant abundance and distribution, both across and within species. In response to water limitation, plants have evolved numerous morphological, physiological, and phenological adaptations. In both well-watered and water-limited conditions, we identified considerable natural variation in drought-related whole-plant and leaf-level traits among closely related members of the Mimulus guttatus species complex that occupy a diversity of habitats in the field.

Lifetime fitness in two generations of Ipomopsis hybrids.

Various models purporting to explain natural hybrid zones make different assumptions about the fitness of hybrids. One class of models assumes that hybrids have intrinsically low fitness due to genetic incompatibilities, whereas other models allow hybrid fitness to vary across natural environments. We used the intrinsic rate of increase to assess lifetime fitness of hybrids between two species of montane plants Ipomopsis aggregata and Ipomopsis tenuituba planted as seed into multiple field environments.

Review. The strength and genetic basis of reproductive isolating barriers in flowering plants.

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.

Leaf physiology reflects environmental differences and cytoplasmic background in Ipomopsis (Polemoniaceae) hybrids.

Natural hybridization can produce individuals that vary widely in fitness, depending upon the performance of particular genotypes in a given environment. In a hybrid zone with habitat heterogeneity, differences in physiological responses to abiotic conditions could influence the fitness and spatial distribution of hybrids and parental species. This study compared gas exchange physiology of Ipomopsis aggregata, I.

Environmental stressors differentially affect leaf ecophysiological responses in two Ipomopsis species and their hybrids.

The recombination that follows natural hybridization may produce hybrid genotypes with traits that are intermediate or extreme relative to the parental species, and these traits may influence the relative fitness of the hybrids. Here we examined leaf ecophysiological traits that may influence fitness patterns in a natural plant hybrid zone. We compared the biochemical photosynthetic capacity of Ipomopsis aggregata, I.

Ecophysiology of first and second generation hybrids in a natural plant hybrid zone.

Hybrids between related species vary widely in relative fitness, and that fitness can depend upon the environment. We investigated aspects of physiology that might influence fitness patterns in a plant hybrid zone. Seeds of Ipomopsis aggregata, I.

Cytoplasmic and nuclear markers reveal contrasting patterns of spatial genetic structure in a natural Ipomopsis hybrid zone.

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.