Drosophila Research

We are studying the process of species divergence and the genetics of speciation in Drosophila pseudoobscura and close relatives using population genetic data and genomic approaches.

The history of divergence of closely related species of Drosophila

We are interested in understanding the roles of gene flow and natural selection during speciation. One way to disentangle the history of closely related species and study speciation is by using large multilocus data sets of DNA sequences and to fit that data to coalescent models of population divergence. By including multiple loci it is possible to make inferences regarding historical gene flow and natural selection that have occurred on some, but not all loci in the genome. One can therefore investigate whether different regions of the genome of incipient species have undergone more gene flow than others. We studied the divergence between Drosophila pseudoobscura and its close relatives D. pseudoobscura bogotana and D. persimilis using a dataset that included 16 loci. We identified regions of the genome in which these species have or have not exchanged genes, and showed that those regions corresponded to regions associated with reproductive isolation. Our results match the prediction that natural selection should impede introgression at regions of the genome that are involved in reproductive isolation and/or associated with species-specific adaptations.

We have continued this work by conducting a finer scale study on the second chromosome of D. pseudoobscura and D. persimilis in order to investigate the effect of inversions on interspecific introgression (in collaboration with Mohamed Noor, Duke University). We have also conducted a similar study in the D. mojavensis-D. arizonae species pair in collaboration with Therese Markow (UCSD).

Functional genomics and the study of speciation in Drosophila

Changes in the timing and the level of gene expression have been long suggested to be fundamental for generating evolutionary change and to play a major role in the adaptation process. Furthermore, changes of gene expression patterns due to gene incompatibilities in the genome of interspecific hybrids have been suggested to play an important role in the generation of reproductive isolation. The advent of new technology that allows looking at patterns of gene expression on a genomic scale, using microarrays or RNA sequencing, provides the opportunity to start testing those suggestions. Microarrays have become a powerful tool to identify relevant genes for evolutionary studies, and can become an important complement to classical genetic and developmental approaches to understand the genetic basis of speciation and the phenotypic divergence of species. We are studying transcriptome evolution in D. pseudoobscura and its close relatives (D. persimilis and D. pseudoobscura bogotana) using microarrays and whole transcriptome sequencing.

All contents copyright © 2009 Carlos Machado. All rights reserved.