My research interests are in the mechanisms of evolution in natural populations. In approaching this problem, the Campbell lab uses a diverse set of approaches, including large-scale field experiments, laboratory and greenhouse experiments, molecular analyses, and computer modeling.



1. Hybrid Zones and 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 using hybrid zones between two species of Ipomopsis (Polemoniacea) to test 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). We are also examining the genomic basis of traits critical to reproductive isolation. Our base for this work is the Rocky Mountain Biological Laboratory (RMBL) in the Colorado mountains. Although both of these Ipomopsis species are native to the area, other hybrid zones can involve movement of genes from an introduced species into a native one, or between a crop plant and surrounding natives.


PovertyGulchhybridzonemeasuring photosynthesisIpomopsis hybrids


Hybrid zone in CO mountains, measurements of photosynthetic gas exchange, and two species of Ipomopsis (left upper corner and left bottom corner) along with F1 and F2 hybrids


2. Natural Selection of Multimodal Trait Associations

We are taking an experimental approach to understanding selection on combinations of traits. Such trait combinations can be subject to correlational selection that arises from synergistic effects of multiple traits. We use experimental methods to test evolutionary hypotheses about ways that correlational selection can be generated, using flowers as a model. This work began through our studies of how insect pollinators respond to flower color and other floral traits of alpine plants in New Zealand (Campbell et al. 2010, 2012).








Currently we are using three species in the Polemoniaceae that grow in the Colorado Rockies to test whether animal responses to multiple traits can generate correlational selection through the use of different sensory modalities, such as vision and olfaction. Floral fragrances are sampled and analyzed with gas chromatography-mass spectrometry (in collaboration with Robert Raguso and Andreas Juergens) to identify key compounds used in subsequent tests of insect behavior in the field.



Reflectance spectra for natural flowers and those phenotypically manipulated


Hawkmoths approach flowers of Ipomopsis aggregata at night only after the volatile indole is experimentally added.

3. Pollination, Plant Demography, and Global Change

I have a long-term interest in how low levels of pollination influence the ecology or evolution of plant populations. One recent collaborative effort, with Mary Price, Nick Waser, and Alison Brody, focuses on how pollination level and seed input impact the demography of I. aggregata (Price et al. 2008, Waser et al. 2010). In addition, the lab is now examining impacts of invasive species and of climate change on levels of pollination. We have shown that rainfall reductions favor the production of more flowers by hybrid Ipomopsis, which could lead to alterations in hybrid zones (Campbell and Wendlandt 2013). PhD student Daniela Bruckman is now investigating the impact of invasive Brassica nigra on the pollination of native plants in coastal sage scrub and grasslands in Southern California. PhD student Kate Gallagher is investigating impacts of early snowmelt in the Colorado Rockies on pollination of Mertensia ciliata mediated by changes in soil moisture.


Greenhouse experiment on impacts of heterospecific pollen on seed set in Phacelia. Photo by D. Bruckman.

4. Evolution of Breeding Systems

About three quarters of flowering plant species are hermaphrodites with both male and female reproductive functions in the same flower. But plants also exhibit a bewildering variety of other breeding systems, including not only dioecy (separate sexes), but also such systems as gynodioecy (female plants and hermaphrodite plants), andromonoecy (male and hermaphroditic flowers on the same plant. One general explanation for this remarkable diversity is offered by sex allocation theory. Currently I am collaborating with Ann Sakai and Stephen Weller on a quantitative genetic experiment on sex allocation in Schiedea (Weller et al. 2007, Sakai et al. 2008, Campbell et al. 2011). We are investigating whether the evolutionary trend towards dioecy hypothesized on the basis of phylogenetic studies can be produced with artificial selection.


Hermaphroditic Schiedea salicaria (Caryophyllaceae). Photo by N. Kawakubo.