Hadfield Group

When individuals interact they may determine each other's phenotype and therefore each other's fitness. As a consequence, variation in a trait across individuals may arise from genetic differences that directly affect the expression of the trait, but also from genetic differences that indirectly affect the expression of the trait in others. When these indirect effects are large the standard quantitative genetic approach can fail to accurately predict the rate, or even the direction of evolutionary change, particularly when individuals that interact are also kin. Although we do some theoretical work in this area, our main interest is in getting much-needed empirical data to obtain accurate estimates of the magnitude of these indirect effects and determining whether they covary with the direct effects. In an on-going long-term experiment we manipulate the composition of families of blue tits (currently 4500 birds from 600 families) so that we can distinguish the direct effect of genes from the indirect effects of genes expressed in siblings and also parents. Combining this information with fitness data we hope to develop and parameterise quantitative genetic models that incorporate the consequences of these kin interactions.

Environmental conditions can change in both time and space, and organisms can respond directly to these changes through phenotypic plasticity or indirectly through evolutionary change. Both plasticity and evolution are known to contribute to geographic variation in many traits in many species. In collaboration with Ally Phillimore we are interested in the relative importance of these two processes, and to what extent they vary across taxa. In order to measure the strength of these two processes for taxa where reciprocal transplant studies are not feasible, we developed a statistical approach for separating the two types of contribution using spatiotemporally replicated data. Like much theory on the spatial evolution of quantitative characters the approach assumes an island model and we are currently working on theoretical and statistical models that are spatially explicit. We hope such models will shed light on the spatial scale of local adaptation and the magnitude of migration load.

Both the quantitative genetic approach and the phylogenetic comparative approach study the effects of shared ancestry. Unsurprisingly, the analytical tools used by the two approaches share a lot in common. In collaboration with groups mainly working on host-parasite evolution we have started to apply quantitative genetic tools to address phylogenetic comparative problems. These collaborations include work on humans and HIV, Drosophila and Sigma virus, small mammals and their fleas, and aphids and their endosymbionts. They range from questions that only concern the evolutionary history of the parasites in isolation, or the hosts in isolation, to more complex analyses that consider the evolutionary histories of both parties and how they interact. More recently, we have started to apply phylogenetic comparative approaches in order to address quantitative genetic questions, such as what determines between-species differences in the amount of heritable variation and can it be predicted from between-species differences in neutral molecular diversity.