The Campbell lab examines evolution in natural populations. Three research topics make use of the closely related plant species Ipomopsis aggregata and I. tenuituba as a model ecological system. Our base for this field work is the Rocky Mountain Biological Laboratory in the Colorado mountains. Other projects examine the influence of climate and invasive species on pollination of plants native to southern California.
- 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), and seed production declines. We are now examining the potential for evolutionary response in functional vegetative traits. In addition to measuring selection in natural populations (with 18 years of data), we are testing impacts on selection experimentally by manipulating snowmelt date and summer precipitation. These manipulations also demonstrate plasticity of traits (Powers et al. 2021).
2. 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).
3. Floral volatile emissions and their evolution in response 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 examined how the combination of responses by pollinators (hummingbirds and hawkmoths) and seed predators (flies) that influence fitness at different points in the life cycle generate patterns of selection on combinations of traits (Campbell et al. 2021). Floral fragrances are sampled and analyzed with gas chromatography-mass spectrometry to identify key compounds used in tests of insect behavior and to determine how floral emissions are changed by environmental conditions such as water availability (Campbell et al. 2019) and temperature.
