Current projects Evolutionary Medicine Research objectives in this area centre on two broad topics: (1) the evolution of pathogen virulence, and (2) the evolution of senescence. (1) Evolutionary theory is challenging the deeply entrenched notion that successful pathogens eventually evolve toward benign coexistence with their hosts. Emerging theory and experimental data have revealed that the degree of evolved virulence (defined as parasite-induced host mortality) depends on the ecology of both host and parasite. The challenge for theoreticians and empiricists is to discover the specific factors that direct virulence evolution. We are currently exploring a number of open theoretical questions in this area, including questions involving the quantitative genetics of virulence evolution, virulence evolution in multi-host and more realistic ecological settings, and virulence evolution in spatially structured populations. (2) Senescence is the deterioration in reproductive potential of an organism as it ages. There are two main hypotheses for the evolution of senescence, the mutation accumulation (MA) hypothesis, and the antagonistic pleiotropy (AP) hypothesis. The MA hypothesis asserts that age-specific deleterious mutations reach a higher frequency for later ages as a result of the declining strength of selection. The AP hypothesis asserts that there is a trade-off between reproductive success early and late in life. Since the strength of selection declines with age, early reproduction is favoured at the expense of late. These theories have been treated largely as alternative hypotheses, but evidence for both is often found. We are currently exploring models that examine the interplay between these two hypothese as well as models that explore the evolution of senescence in more realistic ecological settings. Sexual Conflict/Sexual Selection Both males and females of many species have evolved surprisingly intricate characteristics that appear to be involved in sexual interactions between the two. Much of the current thinking about how such traits evolve is based on the premise that there is an evolutionary conflict of interest between the two parties over many aspects of mating and reproduction. Over the last few years several papers have been published that contain data bearing on these issues, but as yet there is still no complete quantitative theoretical framework in which to interpret these results. Consequently, there are conflicting opinions about what we should expect to observe under different evolutionary scenarios. In collaboration with Dr. Locke Rowe at the University of Toronto we are developing theoretical models aimed at predicting the outcome of coevolutionary interactions between males and females. We are also constructing theory that explores a number of related issues with the field of sexual selection, including the effects of spatial population structure, and the interplay between orgnismal life history patterns and evolution, and the evolution of male secondary sexual characters. A related project will also focus on drawing out the theoretical connections between various models of sexual selection and the theory of sexual conflict. Genomic Conflict and Imprinting One of the most intriguing types of evolutionary conflict documented occurs at the genome level. It need not be the case that different loci within a genome, or even different alleles at the same locus within a genome be acted upon in the same way by natural selection. For example, there is now good empirical evidence and theory suggesting that natural selection acts differently on alleles depending upon their parent of origin. In some cases this conflict appears to have resulted in the evolution of differential allelic expression depending upon whether the allele was inherited maternally or paternally (genomic imprinting). Although a strong body of theory has been developed to explain this specific phenomenon, the evolutionary processes involved are actually very general. We are using the mathemtical tools of kin selection to construct a more general theory of genomic conflict to understand how the form of genomic conflict that has resulted in the evolution of imprinting is related to other evolutionary conflicts. This theory is intended to illustrate how conflict between alleles owing to their 'parent of origin' is a special case of a much more general phenomenon of evolutionary conflict between different 'classes' of alleles. Effects of Spatial Population Structure on Evolutionary Change It has long been known that limited movement of organisms (population viscosity) can result in the genetic structuring of populations, and this can have important evolutionary consequences. We are exploring the evolution of resource exploitation strategies and life history characters in such spatial contexts, as well as how how such spatial structuring affects speciation. An important related project involves virulence evoluton in a spatial context. Many host-parasite systems have distinct spatial components. For example, avian malaria in the Hawaiian islands has had catastrophic effects on the native bird fauna, but the extent of this effect has a strong spatial signal mediated through an altitudinal gradient. Understanding virulence evolution in such contexts, where the epidemiological parameters change throughout space, is of basic interest and it has important applied significance as well. We are developing explicit spatial models of virulence evolution, both by individual-based simulation models and analytical theory to explore these issues.
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