Ecological divergence and the evolution of reproductive isolation

Does ecological divergence necessarily lead to the evolution of reproductive isolation? I am pursuing this question for my Ph.D. research. Many cases that link ecological divergence to speciation are circumstantial; perhaps there is no suitable environment for intermediate hybrids, or maybe there is assortative mating based on phenotype. What links ecological divergence and reproductive isolation in one system probably does not hold water in another. I am using computational and empirical approaches to try and identify a general process (or processes) that link them. This work is just getting under way and I’ll have more to share soon!

Plant evolution in urban environments

During my M.Sc. I worked on understanding how urban environments can affect the evolution of wild plants. When I started this work, urban environments were very underutilized systems for testing questions in evolutionary biology. Cities are replicated spatially and temporally, and all probably exert similar selection pressures on natural populations. By capitalizing on this ‘urbanization experiment’ we tested ideas about the repeatability of evolution, and uncovered some surprising details about what drives evolution in cities. Ongoing work is being led by James Santangelo & Amanda Nelson in Marc Johnson’s EvoEco Lab. I am starting to think about speciation in urban environments… more soon on this front!

Relevant publications

Thompson KA, Renaudin M and MTJ Johnson. 2016. Urbanization drives the evolution of parallel clines in plant populations. Proceedings of the Royal Society B: Biological Sciences. 283:20162180. doi: 10.1098/rspb.2016.2180.

Johnson MTJ, KA Thompson and HS Saini. 2015. Plant evolution in the urban jungle. American Journal of Botany 102(12): 1–3. doi:10.3732/ajb.1500386.

Antiherbivore defenses and natural selection on plant reproductive traits 

Trifolium repens (Fabaceae) growing in a field experiment at the Koffler Scientific Reserve.

Trifolium repens growing in a field experiment at the Koffler Scientific Reserve.

Also during my Master’s research at the University of Toronto Mississauga, I investigated the evolutionary relationship between antiherbivore defenses and plant reproductive traits. This research was motivated by the observation plant defense and reproductive traits are often correlated, but we didn’t know whether variation in defense actually changed selection on traits involved in reproduction. We did two field experiments to test this idea in different plant species. In both experiments, we found natural selection is considerably different for plants that have defenses relative to those that do not.

Relevant publications

Thompson KA, Cory KA and MTJ Johnson. 2017. Induced defences alter the strength and direction of natural selection on reproductive traits in common milkweed. Journal of Evolutionary Biology. In press. doi: 10.1111/jeb.13045.

Thompson KA and MTJ Johnson. 2016. Antiherbivore defenses alter natural selection on plant reproductive traits. Evolution 70(4): 796–810. doi: 10.1111/evo.12900.

Ecological consequences of genome duplication

During my undergraduate program at the University of Guelph, I worked with Dr. Brian Husband and Dr. Hafiz Maherali studying the ecological consequences of genome duplication (polyploidy).  One of the most immediate consequences of genome duplication is an increase in cell size. In plants, cell size is correlated with the width of xylem conduits—vascular tissue that transports water from the roots to the leaves. Consequently, polyploid plants typically have wider xylem conduits than conspecific diploids. Wider xylem conduits confer elevated drought tolerance, and so polyploids are  typically more tolerant of drought than diploids.  How exactly the increased drought tolerance due to polyploidy affects the ecology of plants is unclear, however. For my undergraduate thesis, I conducted two projects using Chamerion angustifolium (Onagraceae), fireweed, to explore the ecological consequences of polyploidy. First, I examined the climatic envelopes of diploids and tetraploid populations sampled in the field. And second, I conducted a greenhouse experiment to determine whether tetraploid plants were better competitors than diploids under drought. See photos from the greenhouse experiment.


Flower of Chamerion angustifolium. Photo by Brian Husband.

Relevant publications

Thompson KA, BC Husband and H Maherali. No influence of water limitation on competitive interactions between diploid and tetraploid Chamerion angustifolium (Onagraceae). Journal of Ecology 103(3), 733–741.

Thompson KA, BC Husband, and H Maherali. Climatic niche differences between diploid and tetraploid cytotypes of Chamerion angustifolium (Onagraceae). American Journal of Botany 101(11) 1868–1875. 

Using DNA-based species identification to improve field surveys

During my time at Guelph, I worked with Dr. Steven Newmaster to determine whether DNA-based species identification can be used to improve the accuracy and cost-effectiveness of vegetation surveys in the field. This work was featured in an issue of the Barcode Bulletin Newsletter.

Relevant publication

Thompson KA and SG Newmaster. 2014. Molecular taxonomic tools provide more accurate estimates of species richness at less cost than traditional morphology-based taxonomic practices in a vegetation survey. Biodiversity and Conservation 23(6): 1411-1424.

Function of mucilage in Brasenia schreberi

On a canoe trip to Algonquin Park in May of 2014 with the Husband Lab, I came across a very strange aquatic plant called the water shield (Brasenia schreberi [Cabombaceae]) that was covered in slime (formally: mucilage). Surprisingly, nobody had tried to figure out what—if anything—this stuff did for the plant. When I returned to Algonquin for a field course in August of 2014, I worked with some students from the U of Guelph to experimentally test the relationship between mucilage and herbivory on leaves. This work was featured as an Editor’s Choice Selection by Canadian Science Publishing.

Mucilage on petiole and abaxial leaf surface of Brasenia schreberi (Cambombaceae). Photo from the University of South Carolina Herbarium.

Mucilage of Brasenia schreberi. Photo from the USC Herbarium.

Relevant publication

Thompson KA, Sora DS, Cross KA, St. Germain JM, and K Cottenie. 2014. Mucilage reduces leaf herbivory in Schreber’s water shield, Brasenia schreberi J. F. Gmel. (Cabombaceae). Botany 92(5): 412-416.

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