|Dr. Mark Johnston
A.B. (Harvard, 1982)
PhD (Chicago, 1990)
| Teaching & Research
Evolution, ecology and genetics of plants, mutation rate, polyploidy, natural selection, mating systems, self-fertilization, flower development, molecular evolution.
am interested generally in the forces that shape the evolution of plants, and more specifically in plant reproduction. Unlike most animals, the vast majority of plant individuals possess both female and male sexual organs. This raises a number of interesting issues: How much should an individual self-fertilize? Does self-fertilization cause populations to go extinct? In addition to their use in addressing these kinds of questions, plants are also very useful for addressing other issues of fundamental importance to evolutionary biology, not just plant evolutionary biology. Such topics include: the rate of appearance of new, harmful mutations; the effect of continued inbreeding on fitness; differences in rates of evolution between genes transmitted maternally vs. paternally; etc., etc.
We have recently discovered that a sperm transmits more mutations than an egg (Whittle and Johnston, 2002, 2003), and several projects are underway to understand the extent and causes of this phenomenon.
We use a variety of techniques to study these sorts of questions, including: field work; greenhouse propagation; the lab work (e.g., DNA sequencing, AFLPs, image analysis, electron and confocal microscopy, etc.); and theoretical modeling. Graduate training emphasizes the concepts of evolutionary ecology and evolutionary genetics, as well as the statistical analysis of data.
|Examples of Students' Research
Whittle, C.-A., and M.O.Johnston. 2003. Male-biased transmission of deletvious mutations to the progeny in Arrabidopsis thaliana. Proc. Natl. Acad. Sci. USA 100: 4055-4059.
Whittle, C.-A., and M.O.Johnston. 2003. Broad-scale analysis contradicts the theory that generation time affects molecular evolutionary rates in plants. J. Mol. Evol. 56: 223-233.
Whittle, C.-A., and M.O. Johnston. 2002. Male-driven evolution of
mitochondrial and chloroplastidial DNA sequences in plants. Molecular
Biology and Evolution. 19: 938-949.
Whittle, C.-A., T. Beardmore and M.O. Johnston. 2001. Is G1 arrest in plant seed induced by a p53-related pathway? Trends in Plant Science (6: 248 - 251).
Simons, A.M., and M.O. Johnston. 2000. Plasticity and the genetics of reproductive behaviour in the monocarpic perennial, Lobelia inflata (Indian tobacco). Heredity 85:356-365.
Simons, A.M., and M.O. Johnston 1999. The cost of compensation. American Naturalist 153: 683-687.
Li, P., and M.O. Johnston 1999. Evolution of meiosis timing during floral development. Proceedings of the Royal Society B: Biological Sciences 266: 185-190 (and cover photo).
Johnston, M.O. 1998. Evolution of intermediate selfing rates in plants: Pollination ecology versus deleterious mutations. Genetica 102/103: 267-278 (special issue, Mutation and Evolution. Published in book form as well by Kluwer Press).
O'Connell, L.M., and M. O. Johnston 1998. Male and female pollination success in a deceptive orchid, a selection study. Ecology 79: 1246-1260.
Johnston, M.O., B. Das, and W.R. Hoeh 1998. Negative correlation between male allocation and self-fertilization in a hermaphroditic animal. Proceedings of the National Academy of Sciences USA 95: 617-620.
Simons, A.M., and M.O. Johnston 1997. Developmental instability as a bet-hedging strategy. Oikos 80: 401-406.
Johnston, M.O., and D.J. Schoen. 1996. Correlated evolution of self-fertilization and inbreeding depression: An experimental study of nine populations of Amsinckia (Boraginaceae). Evolution 50: 1478-1491.
Johnston, M.O., and D.J. Schoen. 1995. Mutation rates and dominance levels of genes affecting total fitness in two angiosperm species. Science 267: 226-229 (and cover photo).Links