A major goal of our research is to link genotype to phenotype in the process of adaptation and the evolution of reproductive isolation. We study how traits that contribute to reproductive isolation and adaptation evolve through the interaction of migration, drift, and selection. Our work focuses on Phlox, a charismatic genus of flowering plants with a rich history of ecological and evolutionary study. We use Phlox to investigate an ever-increasing range of topics including plant-pollinator interactions, the evolution of self-incompatibility, and the process of reinforcement.
Reinforcement is the process by which reduced hybrid fitness generates selection for the evolution of reproductive isolation between emerging species. This is an important way in which natural selection can contribute to the process of speciation. We use molecular biology, population genetic analyses, and field-based selection experiments to investigate reinforcement in two Texas wildflowers, Phlox drummondii and Phlox cuspidata.
Both species of Phlox produce light blue flowers throughout most of their ranges, but P. drummondii has dark red flowers in eastern populations that are sympatric with P. cuspidata. Our work has shown that this change in flower color is caused by reinforcement. Using common garden field experiments, we determined that dark-red flowered plants produce nearly half as many hybrids as light-blue flowered plants. Hybrids have high sterility and therefore this reduction in hybridization is favored by reinforcing selection. This work represents the first time reinforcement was measured under natural field conditions.
We followed up this work by estimating the strength of reinforcing selection acting on flower color variation. We combined field observations of the change in flower color over geographic space with a spatially explicit population genetic model. Our results indicate that selection is very strong and acts to favor dark red flowers in sympatric populations and light blue flowers in allopatric populations.
Suni, Sevan S. and Robin Hopkins. 2018. The relationship between postmating reproductive isolation and reinforcement in Phlox. Evolution 72(7):1387–1398 [PDF]Continue reading →
Roda, Federico, Fábio K. Mendes, Matthew W. Hahn, and Robin Hopkins. 2017. Genomic evidence of gene flow during reinforcement in Texas Phlox. Molecular Ecology 26: 2317-2330. [PDF]Continue reading →
Hopkins, Robin, Rafael F. Guerrero, Mark D. Rausher, Mark Kirkpatrick. Strong reinforcing selection in a Texas wildflower. 2014. Current Biology 24:1995-1999. (Featured in Current Biology Dispatch by Daniel Matute and Daniel Ortiz-Barrientos) [PDF]Continue reading →
Hopkins, Robin, Rausher, Mark D. The cost of reinforcement: Selection on flower color in allopatric populations of Phlox drummondii. 2014. The American Naturalist 183: 693-710. [PDF]Continue reading →
Hopkins, Robin. 2013 Reinforcement in plants. New Phytologist 197: 1095-1103 [PDF]Continue reading →
Hopkins, Robin, Mark D. Rausher. 2012. Pollinator-mediated selection on flower color allele drives reinforcement. Science 335: 1090-1092. (Featured in Current Biology Dispatch by John Pannell) [PDF]Continue reading →