Hybrid zones as a natural laboratory for measuring mechanisms of ecological speciation
The mechanisms by which new species form is one of the central issues in evolutionary biology. In ecological speciation, reproductive isolation between incipient species arises as a result of divergent natural selection between environments. We are testing two major mechanisms of ecological speciation in plants. One mechanism relies on pollinator-mediated divergent selection, and the other relies on divergent selection imposed by other features of the habitat. This requires us to take approaches ranging from long-term reciprocal transplants (Campbell et al. 2008) to studying behavior of hummingbird pollinators (Aldridge and Campbell 2007) to measuring physiological traits such as photosynthetic rate and water use efficiency (Campbell et al. 2013).
Predicting evolution in response to climate change and how that impacts the demography of plant populations
Evolutionary rescue is a process in which a population responds to a new selective regime rapidly enough that the increase in absolute fitness outpaces negative demographic effects. We are capitalizing on three decades of research with Ipomopsis to measure how natural selection on multiple traits is altered by increased drought under climate change and the evolutionary and demographic consequences. Natural selection of flower traits by animal pollinators is less intense in years with early snowmelt (Campbell and Powers 2015). We are now examining the potential for evolutionary response in functional vegetative traits.
Selection on floral volatile emissions and other traits due to pollinators and herbivores
We are taking an experimental approach to understanding selection on combinations of traits, with an emphasis on floral volatile emissions. Production of a minor component of the scent in Ipomopsis attracts hawkmoths to approach inflorescences (Bischoff et al. 2015). Flower color then influences whether or not the moth inserts its proboscis, effecting pollination. We are currently testing whether the combination of responses by pollinators (hummingbirds and hawkmoths) and seed predators (flies) that influence fitness at different points in the life cycle can generate correlational selection on combinations of traits. Floral fragrances are sampled and analyzed with gas chromatography-mass spectrometry to identify key compounds used in subsequent tests of insect behavior in the field.