Male-biased infection is a common trend in vertebrate-parasite systems and male-biased transmission has been demonstrated for rodent micro- and macroparasite systems.  Males, compared to females, contribute a disproportionally higher number of infective stages and are responsible for a larger proportion of transmission; implying that males are the super-spreaders of disease within a population. A proposed mechanism that creates super-spreaders is the level of testosterone within an individual. Testosterone and parasite intensity have a strong positive correlation possibly due to the immunosuppressive effects of testosterone.  In addition to the effects of high testosterone on host susceptibility, behavioral changes may increase the exposure to parasites, as well as increase transmission events.  To test this, we performed a longitudinal mark-recapture study where we experimentally elevated testosterone levels of male mice in wild populations of Peromyscus leucopus.  We then recorded the changes in the social contact networks to assess the changes in exposure and potential transmission in relation to elevated testosterone levels.

Results/Conclusions

We found that experimentally elevating testosterone levels maintained or increased the number of contacts between hosts and, as a result, the potential transmission was higher compared to control populations where no testosterone treatment was applied.  Individuals in untreated control populations became less connected over the treatment period in accordance with seasonal behavior.  However, where males had been given testosterone implants, the average network degree and clustering among individuals did not follow seasonal trends and remained high, increasing the transmission potential within the population.  Our results indicate that males with high testosterone levels can maintain increased population level contacts, producing different transmission and social networks compared to those where testosterone is at background levels.  While testosterone has been shown to increase the susceptibility of males, these results demonstrate a mechanism whereby the behavioral effects of testosterone may increase transmission potential of parasites within a population.