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 functional genomic approaches (cDNA and oligo microarrays).

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 Teri Markow (University of Arizona).

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, 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 cDNA microarrays. We have built a cDNA microarray for D. pseudoobscura that we have used to gene expression data from adult individuals of D. pseudoobscura, D. persimilis and their hybrids. We have found strong patterns of hybrid dysfunction asymmetry and breakdown of regulation of genes involved in respiratory metabolism in both male and female hybrids.

An NSF grant has been funded to support this research (DEB-0520535 ). We are using a whole-genome microarray of D. pseudoobscura to obtain gene expression profiles during the development of male and female D. pseudoobscura, D. persimilis, D. p. bogotana, pseudoobscura/persimilis F1 hybrids, and pseudoobscura/bogotana F1 hybrids. With these experiments we will identify misexpressed genes in hybrid males that are known to be involved in reproduction or spermatogenesis and are thus potential candidate genes for hybrid male sterility in this group. We will then characterize a subset of the reproductive-related misexpressed genes by: a) determining whether gene expression and hybrid male sterility are correlated across five generations of backcross; b) mapping the genetic basis of expression differences in confirmed candidates in order to determine whether expression differences are due to cis or trans-regulatory factors; c) conducting basic molecular evolution and population genetic studies in all confirmed candidate loci, to determine the extent to which selection has driven their divergence. If the technology is available we plan to apply transgenesis techniques to study the phenotypic effects of candidate genes in the genomic background of each sibling species. In principle, the identification of “speciation genes” from this group of Drosophila will allow us to ask whether the evolution of mechanisms of reproductive isolation is due to the same set of genes across different species.

All contents copyright © 2005 Carlos Machado. All rights reserved.