Thomas Fredrik Hansen
I am a theoretical evolutionary biologist who uses mathematical modeling as my chief research tool. I have background and interests in mathematical and statistical modeling within a wide range of topics including population genetics, population dynamics, and phylogenetic analysis.
Most of my current research is focused at the interface between evolutionary genetics and trait adaptation. Evolutionary theory contains a sophisticated and detailed account of how adaptations are produced and maintained by natural selection, but selection is based on available genetic variation and the 'variational' properties of organisms are less well understood. A major challenge for evolutionary biology is to understand the laws of organismal variation and how they relate to evolutionary change. Some of the questions I ask in my research are: 1) To what extent is the observed genetic variation of a character available to build adaptations, and to what extent is it constrained by conflicting selection pressures and pleiotropic interactions with other characters? 2) What are the properties of new mutations and how do these properties affect adaptation? 3) How do the effects of genes and mutations depend on the genetic background? 4) What determines the genetic architecture of a trait? 5) How do the variational properties of organisms evolve? 6) What makes a character evolvable and how does evolvability evolve? I pursue these questions in a number of different theoretical and empirical projects. Some of my ongoing projects are:
Modeling the evolution of genetic architecture
One approach to answer these questions is to study the evolution of genetic architecture through mathematical modeling. Much of this work is based on a general model of gene interactions that I developed in collaboration with Günter Wagner (Yale Univ.) and Joachim Hermisson (Univ. of Munich). Through simulation and analytical techniques we use this model to study the evolution of mutational properties and gene effects, as well as the evolution of the genotype-phenotype map itself. A related project uses the model as a statistical tool to estimate aspects of genetic architecture from various types of genetic data. I also work to develop models of gene-regulatory networks.
Variation and adaptation in Dalechampia blossoms
In collaboration with Scott Armbruster (Univ. of Portsmouth) and Christophe Pélabon (NTNU, Trondheim), I use quantitative genetic methods to study floral variation in Dalechampia vines. The 'blossoms' of these plants are functionally integrated inflorescences that secrete resin from a specialized gland to attract bees that use resins as nest-building materials. We seek to characterize the variability and evolvability of the blossoms and relate this to adaptive diversity among populations and species. Currently, we have an NSF grant through Florida State Univ. and Univ. of Alaska for this work.
The genetic architecture of Drosophila wing morphology
In collaboration with David Houle (Florida State Univ.), I study the genetic architecture of fruit-fly wing morphology through artificial selection and genetic experiments. Fly wings are interesting as they exhibit an extreme degree of stasis across species. We try to understand whether there are variational constraints that keep the wings stable. This work is funded by NSF and is being carried out at Florida State Univ.
Model-based phylogenetic comparative methods
In a long-standing project initiated in collaboration with Emilia Martins (Univ. of Indiana) and currently in collaboration with Steven Orzack (Freshpond Res. Inst.) and Jason Pienaar (Florida State Univ.), we develop statistical methods for analysis of comparative data based on explicit models of adaptive evolution. We seek to develop methods that are both statistically sound and make reasonable biological assumptions about adaptation and phylogenetic inertia.