Parasite phenotypic plasticity

Isolation-by-distance x isolation-by-time simulation

Previous work by Hendry and Day (2005) modelled isolation-by-time (IBT) for an asexual population and considered two traits: reproductive time and body size, a trait they consider to have variable fitness along a temporal cline. While their work is a foundation to our own, their results reflect weak selection and perfect heritability for body size, which, coupled with asexual reproduction, have limited application to real-life population dynamics. To expand upon their investigation, we are modelling a sexually reproducing flowering plant population that can be manipulated for a number of parameters related to IBT and isolation-by-distance (IBD). With this model, we hope to answer:

1. Does IBT between early and late flowering plants amplify temporal genetic structure for the flowering time trait by building linkage disequilibrium among alleles with similar phenotypic effect, i.e., if a plant has an ‘early’ allele at one flowering time locus, is it more likely than by chance to have ‘early’ alleles at the other flowering time loci?
2. Does the temporal genetic structure for flowering time interact with limited pollen and seed dispersal to create spatial population genetic structure for flowering time, i.e., over time, do early and late plants cluster over the landscape more tightly than by chance?
3. Does the temporal genetic structure amplify linkage disequilibrium among neutral loci and alter the impact of genetic drift?

Maintenance of genetic variation in pollen competiveness in mixed-mating systems

If a gene has consequences that affect both haploid and diploid phases of a plant’s life cycle and there is dominance involved in the gene locus, then a recessive deleterious allele can be protected in a diploid that is heterozygote. This same allele would be exposed in a haploid that carries this recessive deleterious allele alone. The exposure of this deleterious allele would thus put the gamete that holds this allele at a fitness disadvantage. Such a scenario then posits a theory that genes that have adverse effects on the gametic phase will be purged by natural selection. Such deleterious recessive genes should not be found to have strong effects on gamete performance, because if they did they would consequently be eradicated by natural selection. This project uses a population genetics model to explore the potential for genes that have deleterious effects on gamete competition to be maintained in the population as a result of assortative mating, which would consequently lead to assortative competition among gametes. If early flowering plants produce largely strongly competitive pollen, it follows that the effect of being a strongly competitive pollen grain would be essentially neutral, as the strongly competitive pollen grain would not have an advantage against its competitors. Similarly, late flowering plants that produce weakly competitive pollen would find their pollen in a similarly competitively neutral environment, as a weakly competitive pollen grain would not be at a disadvantage against its competitors. In other words, the overall success rate of early and late flowering plants could be same if like competes with like in terms of flowering time and therefore pollen competitiveness.

Our work features two forms of assortative mating, fixed and mass-action:

1. Fixed - Fixed selfing can be considered two different ways. Either a certain proportion of a population is entirely while the remaining individuals are entirely outcrossing, or- more realistically- a certain proportion of ovules per maternal plant receive entirely self pollen while the remaining ovules receive outcross pollen.
2. Mass-action - An individual's ovules are able to receive both self and outcross pollen; however, a certain proportion of the entire pollen load that an individual receives is self pollen with the remaining pollen being outcross.

This projects features both numerical and analytical results based on recursion equations describing changes in genotype frequency over generations.