Parasitic Personalities: Consistent Individual Differences in Behavior in a Facultatively Parasitic Mite

Host attachment is a necessary behavior in the evolution of parasitism. It is hypothesized that populations pass through a stage of facultative parasitism before the evolution of obligate parasitism. Previous research has revealed the impact of extrinsic factors on the expression of parasitic tendencies, but to our knowledge, the role of individual behavioral variation driving parasitic tendencies remains to be tested. Here, we used repeated behavioral assays to quantify attachment propensity and activity level of individual Macrocheles muscaedomesticae, facultatively parasitic mites of flies, from two different populations. Mites from both populations exhibited repeatability in attachment propensity and mites from one population exhibited repeatability in activity level. We did not find a relationship between an individual's activity level and attachment propensity. Our data suggest that facultative parasitism may not simply describe a phenotypically plastic strategy that responds to environmental cues, but perhaps that individual differences in parasitic tendencies may appear like facultative parasitism at the population or species level.