Molecular Population Genetics of Demodex folliculorum

The follicle mite, Demodex folliculorum, lives in the follicles and sebaceous glands of human skin. In fact, D. folliculorum is one of the most common permanent ectoparasites of humans. Despite their prevalence in the human population, little is actually known about these mites. The Palopoli lab has begun to study variation in the mitochondrial genome of D. folliculorum. Last semester, in the process of sequencing mites from Asian hosts, Biology 216 groups found that these Asian mite samples yielded a significantly lower PCR amplification success rate than those from hosts of recent European descent. One explanation for this low amplification rate of the Asian mites is that the primers, which were designed from a mite taken from a host of recent European descent, are simply biased and therefore, unable to amplify the divergent sequences of the Asian mites. Another possibility is that DNA is not being properly extracted from the mites due to their small size and oily texture. This summer, I designed primers in the 18S gene, a highly conserved nuclear gene, in which a higher amplification rate was expected. After many PCR experiments were carried out using mites taken from a host of recent European descent, it was found that the amplification rate had not significantly increased. Therefore, it was concluded that primer ascertainment bias does not exist and that the DNA extraction protocol is responsible for the low amplification rates. Modifications to the protocol were able to increase the amplification rate. Convinced that our results have not been biased, I began sequencing mites from Asian hosts in order to find out more about the nature of D. folliculorum transmission and hostspecificity. So far, the Asian sequences show a significant degree of divergence when compared to mites from hosts of recent European descent.