Hybridization and speciation–hybridization has multiple and varied effects on the speciation process and can be used as a tool to study this process. For example, hybridization and introgression can prevent, slow or reverse population divergence, or be the source of novel combinations of adaptive alleles that might facilitate rapid hybrid speciation. Moreover, segregating variation in hybrid zones can be used to map traits that differ between species, including those that constitute inherent barriers to gene flow. We are interested in hybridization for all of these reasons, and recent or ongoing studies in the lab investigate:

  • the genetic basis and evolution of barriers to gene flow in butterflies, manakins, and stick insects
  • the genetic architecture of morphological and behavioral trait differences between two butterfly species (read more)
  • the nature and repeatability of homoploid hybrid speciation in alpine butterflies (read more)
  • the genome composition of admixed lineages (see our recent review article and work on amazon mollies)

photo by L. Lucas

Genetics of adaptation–considerable uncertainty remains about the genetic basis of adaptation in nature. We still do not know whether adaptation most often occurs from new mutations or standing genetic variation, involves changes at a few or many loci, or involves the same genetic variants in different populations. We are using multiple systems and approaches to advance understanding of the genetic basis of complex adaptive traits and components of fitness, by, for example:

  • coupling field and lab experiments, morphometrics, and genome wide association mapping and admixture mapping in Lycaeides butterflies
  • quantifying the genome-wide response to phenotypic selection in field transplant experiments with Timema stick insects adapted to different host plants
  • testing for gene by gene interactions between a butterfly and its host plant (alfalfa) that affect the fitness of either species

artwork by R. Ribas

Genetic variation in the wild–Understanding what factors determine levels of genetic variation within populations and species or the distribution of genetic variants among populations is central to evolutionary biology and might be important for biodiversity conservation. Along these lines, we are particularly interested in:

  • the relative contribution of different evolutionary processes to the maintenance of genetic variation in nature
  • spatial and temporal variation in the nature, direction, and magnitude of selection in butterflies
  • population structure and conservation genetics

photo by L. Lucas

Statistical models and computational biology–large-scale genome sequencing and resequencing is now possible for many organisms, but making sense of these data requires computational tools and advanced statistical models. More work in this area is needed. In particular, we need models that are sufficiently complex to incorporate multiple evolutionary processes and linkage among variants, but also computationally efficient. We have developed hierarchical Bayesian models to quantify genetic differentiation and introgression using high-througput DNA sequence data (check out our software and software page). Similarly, we have studied several of these models or other aspects of population genomic inference using computer simulations. Current and future research in our lab will develop models and software to:

  • measure evolutionary processes from genome-scale space-time allele frequency data
  • test for evidence of polygenic adaptation
  • study global and local ancestry in admixed lineagesplot

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