Biomedical subjects

Todd A Schlenke

Publications and source records attributed to Todd A Schlenke.

3 recordsLinked to original sources

PubMed2005

Linkage disequilibrium and recent selection at three immunity receptor loci in Drosophila simulans.

Immune system genes in a California population sample of Drosophila simulans were shown to bear several hallmarks of the effects of past directional selection. One potential effect of directional selection is an increase in linkage disequilibrium among the polymorphic sites that are linked to the site under selection. In this study, we focus on three D. simulans immunity loci, Hmu, Sr-CI/Sr-CIII, and Tehao, for which the polymorphic sites are in nearly perfect linkage disequilibrium, an unusual finding even with respect to other immunity genes sampled from the same lines. The most likely explanation for this finding is that, at each locus, two divergent alleles have been selected to intermediate frequencies in the recent past. The extent to which the linkage disequilibrium extends to the flanks of each of the immunity genes is minimal, suggesting that the favored mutations actually occurred within the immunity genes themselves. Furthermore, the excess linkage disequilibrium found in the California population is not found in an African D. simulans population sample and may be a result of novel pathogen-mediated selection pressures encountered during establishment of non-African populations.

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PubMed2004

Strong selective sweep associated with a transposon insertion in Drosophila simulans.

We know little about several important properties of beneficial mutations, including their mutational origin, their phenotypic effects (e.g., protein structure changes vs. regulatory changes), and the frequency and rapidity with which they become fixed in a population. One signature of the spread of beneficial mutations is the reduction of heterozygosity at linked sites. Here, we present population genetic data from several loci across chromosome arm 2R in Drosophila simulans. A 100-kb segment from a freely recombining region of this chromosome shows extremely reduced heterozygosity in a California population sample, yet typical levels of divergence between species, suggesting that at least one episode of strong directional selection has occurred in the region. The 5' flanking sequence of one gene in this region, Cyp6g1 (a cytochrome P450), is nearly fixed for a Doc transposable element insertion. Presence of the insertion is correlated with increased transcript abundance of Cyp6g1, a phenotype previously shown to be associated with insecticide resistance in Drosophila melanogaster. Surveys of nucleotide variation in the same genomic region in an African D. simulans population revealed no evidence for a high-frequency Doc element and no evidence for reduced polymorphism. These data are consistent with the notion that the Doc element is a geographically restricted beneficial mutation. Data from D. simulans Cyp6g1 are paralleled in many respects by data from its sister species D. melanogaster.

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PubMed2003

Natural selection drives Drosophila immune system evolution.

Evidence from disparate sources suggests that natural selection may often play a role in the evolution of host immune system proteins. However, there have been few attempts to make general population genetic inferences on the basis of analysis of several immune-system-related genes from a single species. Here we present DNA polymorphism and divergence data from 34 genes thought to function in the innate immune system of Drosophila simulans and compare these data to those from 28 nonimmunity genes sequenced from the same lines. Several statistics, including average K(A)/K(S) ratio, average silent heterozygosity, and average haplotype diversity, significantly differ between the immunity and nonimmunity genes, suggesting an important role for directional selection in immune system protein evolution. In contrast to data from mammalian immunoglobulins and other proteins, we find no strong evidence for the selective maintenance of protein diversity in Drosophila immune system proteins. This may be a consequence of Drosophila's generalized innate immune response.

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