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.
One area of investigation concerns the role that adaptation from standing genetic variation has in speciation. In collaboration with Matthew Osmond (website) and Dolph Schluter, I am using simulations to evaluate whether standing variation makes speciation between phenotypically similar populations more difficult than ecologically divergent populations. We’ve also investigated how environmental differences among population pairs affects the extent of parallel genetic evolution.
I am conducting a systematic review on the inheritance of hybrid phenotypes. The largest goal is to investigate how common trait ‘mismatches’ are in first-generation hybrids. More soon!
The empirical work is being done with stickleback, and will be a long haul.
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 in Marc Johnson’s EvoEco Lab. We are looking at multivariate adaptation to urbanization gradients, the evolution of sex in urban environments, and global patterns of cyanogenesis cline evolution. I have recently submitted an paper on speciation in urban environments and hope to share this shortly.
Thompson KA, Rieseberg L and D Schluter. Speciation and the city. TREE.
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
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.
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.
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.
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.
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.