An extended epiphenotype for an extended phenotype in Toxoplasma gondii infected feral house mice

Parasitism of mice by Toxoplasma gondii reduces the host's aversion to cat odors, likely increasing predation and transmission of the parasite to its definitive host. This behavioral change suggests a parasitic manipulation where host behavior becomes an extended phenotype of the parasite. Independently, epigenetic changes within an organism are now known to create behavioral change. The results described here provide an experimental connection between these disparate strands of extended phenotypes and the role of epigenetics in behavioral diversity. Using mice captured on Kangaroo Island in Australia, we demonstrate that Toxoplasma gondii infection leads to specific DNA hypomethylation events in the host brain. Previous laboratory studies have shown that these epigenetic changes underlie the central processing of cat odors. We posit that the concept of extended phenotype can be expanded to extended epiphenotype, thus linking parasite genes to host behavior through epigenesis. This phenomenon has broad implications for inter-species relationships.