Population genetic analysis of invasive Rattus: Implications for evolutionary biology, disease ecology and invasion biology

Abstract

Scope and Method of Study: I utilized population genetic analyses to examine the colonization history and contemporary dispersal patterns of invasive Rattus in the U.S., as well as identifying any evolutionary impacts of these invasions (i.e., hybridization). In addition, I used reverse-transcription PCR to examine whether invasive Rattus were competent hosts for zoonotic hepatitis E virus in the U.S., where the source of infections has gone largely unidentified.

Findings and Conclusions: In terms of colonization history, I found that R. rattus and R. norvegicus were characterized by distinct patterns of colonization, with R. rattus colonizing from a single maternal lineage and R. norvegicus colonizing from at least four maternal lineages. In addition, R. rattus do not appear to be establishing in the U.S. at a high rate, nor do they appear to be exhibiting a high frequency of long-distance dispersal. In contrast, R. norvegicus appears to be establishing and dispersing long distances at a very high frequency. In terms of evolutionary impacts, I found that extensive hybridization with introgression is occurring among several black rat species, and introgression is leading to widespread genomic swamping of R. tanezumi by two other species. Finally, I found conclusive evidence that invasive R. rattus and R. norvegicus are capable of carrying the zoonotype genotype 3 of the hepatitis E virus within the U.S., laying the groundwork for future studies investigating their role in human infection.