Summary of our laboratory’s research

Our laboratory’s research is devoted to developing a robust framework for the science of coevolutionary biology. The major problem we are pursuing is how the process of coevolution organizes the earth's biodiversity. Coevolution is reciprocal evolution between interacting species driven by natural selection. It is responsible for many of the major events in the history of life, and it is a major force in the organization of biological communities. The coevolutionary process shapes interacting networks of species at local levels, regional levels, and global levels. It weaves the threads of biodiversity into a rich and resilient fabric.

We now know that coevolution is a relentless process, creating ever-changing geographic mosaics in how species interact with one another. Populations of one species often become adapted to local populations of other species.

We also now know that these local coevolutionary changes can sometimes occur on time scales of less than a hundred years, indicating that there is often no real difference between ecological time and evolutionary time. The challenge, then, is to understand how interactions can be so highly dynamic and yet persist across landscapes and millennia. We therefore work at multiple time scales and spatial scales, studying traits and interactions that evolve rapidly and others that evolve more slowly.

 

 

 

The three major problems to solve

Our lab’s approach has been to divide the study of coevolution into three major problems to solve and then to use a combination of ecological, genetic/molecular, and phylogenetic techniques to analyze coevolution as a hierarchical process.

1) Species are collections of genetically distinct populations. Any theory of how coevolution organizes biodiversity must begin with an understanding of this nearly universal property of species, and of how it influences local adaptation and specialization in interacting organisms.

2) Coevolving interactions are often locally transient and geographically variable, yet many persist regionally for millions of years. An important goal of coevolutionary biology is therefore to understand how the temporal and geographic dynamics of interspecific interactions shape coevolution.

3) Coevolving interactions commonly form networks of species rather than simply pairs of species. The problem to solve is whether coevolution shapes these networks in predictable ways.

Most of the published papers from our laboratory, including my three books on coevolution (Thompson 1982, 1994, 2005), address these three central problems from an increasing diversity of perspectives.

 

Details of some recent and current studies

How do coevolving interactions vary across ecosystems, and what can we learn from these studies to help preserve coevolutionary interactions into the future amid environmental change?

Each local interaction between a pair of species, or among a group of species, is a mini-coevolutionary experiment. By studying the same interaction in multiple ecosystems, and asking how these local populations are genetically connected over large regions, we can start getting answers to how coevolution shapes the web of life over large geographic scales.

That requires interactions that are broadly distributed, are found easily in the field, and are easily manipulated both in the field and in the lab. We have studied a wide range of interactions over the past several decades, but one set of interactions has proven particularly useful. These are the interactions between prodoxid moths and their hostplants. Prodoxids includes the yucca moths that have coevolved with yuccas as their obligate pollinators, the Greya moths that are much more variable in their interactions with plants, and some other species.

The interactions between Greya moths and their hostplants have been particularly useful, because these interactions vary from mutualism to antagonism among ecosystems. Unlike yucca moths, Greya moths feed on small herbaceous plants in the Saxifragaceae and Apiaceae. We have a molecular phylogeny of the moths and the plants, which has helped us understand how the interaction has diverged as it has spread across large regions. We also have developed a large-scale molecular phylogeographic database for Greya politella, the most widely distributed member of the genus, and we have similar genetic data for the two major lineages of hostplants used by Greya politella: Lithophragma and Heuchera. These past and ongoing studies have provided us with a molecular template for understanding how populations, traits, and ecological outcomes with hostplants have evolved across western North America. We are currently focusing on two questions::

• How do coevolving moth and plant traits vary across the thousands of kilometers north to south over which the interaction occurs?

 

• How does coevolution proceed when multiple species are involved in the interaction rather than just a single pair of species?

 

 

 

 

 

 

 

What is the geographic scale of local adaptation in coevolving interactions?

In recent years, we have also used interactions between coastal pines and mycorrhizal fungi to explore questions on the spatial scale of coevolution. These studies have taken advantage of the observation that several species of pine are restricted to a narrow band of coastal environments from Alaska to Baja California, and these pines harbor specialized mycorrhizal fungi in the genus Rhizopogon. That structure makes it easier than in many interactions to interpret the geographic scale of local coadaptation. Jason Hoeksema, a former postdoctoral associate in our lab who is now an assistant professor at University of Mississippi, has led the work on these continuing studies. Christopher Schwind, who is currently our laboratory manager, has been closely involved with the day-to-day maintenance of these studies. This work is reaching completion and we are moving on to other interactions to explore questions on the scale of local adaptation.

 

How do geographic selection mosaics and gene flow shape the rate and trajectory of coevolving interactions?

These studies have used laboratory microcosms of E. coli and T7 phage to explore the dynamics of rapid coevolution. The experiments have been designed to test specific predictions of the geographic mosaic theory of coevolution. The work involves experimentally induced coevolution followed by sequencing of the genes undergoing selection. These studies began as a collaboration between our laboratory and Brendan Bohannan’s laboratory at Oregon State University, with Samantha Forde as the postdoctoral associate who spearheaded this work. Robert Holt from University of Florida and Ivana Gudelj and Robert Beardmore, both from Imperial College, London have been closely involved in the modelling aspects of these studies in recent years. Samantha Forde is now an adjunct faculty member at UCSC, and we continue to collaborate on these studies.

Our laboratory is now also involved in a new collaboration on microbial coevolution with Angus Buckling's laboratory at Oxford University. Postdoctoral associate Britt Koskella is leading that effort. These studies are using Pseudomonas bacteria and bacteriophage to evaluate geographic selection mosaics in a very different kind of interaction between bactieria and phage. One of the goals of these studies is to understand the spatial scale at which local coadaptation, coevolutionary hotspots, and coevolutionary coldspots occur in these interactions in the field, rather than in the lab.

 

How does coevolution shape large webs of interacting species?

Increasingly, we are asking questions about how large groups of species coevolve. These studies are using mathematical models and available data from other laboratories to ask how coevolution may shape the traits and patterns of specialization within large webs of interacting species. We are currently focusing on interactions among pollinators and plants and similar kinds of mutualistic interactions that are crucial for the functioning of most ecosystems worldwide but are under threat in many ecoystems.

Our mathematical studies of coevolving webs are being led by Paulo Guimarães, who was a postdoctoral associate in our lab and is now an assistant professor at the University of São Paulo, Brazil. Pedro Jordano from the Estación Biológica de Doñana in Seville, Spain is collaborating directly with us on this work and Jordi Bascompte, from the same institute, has provided ongoing insights into this work.

We are also collaborating with Victor Rico-Gray from the Instituto de Ecología in Xalapa on analyses of temporal changes in networks of ant-plant interactions in Mexico amid invasion by new ant species. These studies are taking advantage of large datasets that he and Cecilia Diaz, also from the Instituto de Ecología, have collected during the past decade.

 

Other Research Questions

In addition to these questions, we continue to explore a wide range of related questions on the coevolutionary process. These include investigations into how the evolution of plant polyploidy has shaped coevolution between plants and animals, how outcomes of interactions vary temporally on the time scale of decades, and how changes in species ranges and the introduction of novel species may alter the dynamics of coevolution.

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