black rat commensalism

PLoS ONE has an interesting article by Aplin et al. on the history of commensalism in black rats. The team studied mtDNA in rats and found three lineages that relate to prehistoric and historic periods of human population and trade expansion. So, commensalism occurred independently multiple times, and is clearly important for understanding black rat adpatation and biogeography today, as well as the importance of rat-carried pathogens in human history.