EXPERIMENTAL INFECTION WITH A NATURALLY OCCURRING PROTOZOAN PARASITE REDUCES MONARCH BUTTERFLY (DANAUS PLEXIPPUS) MATING SUCCESSY

Parasitic infection is known to drive sexual selection in persuasive mating systems, where parasites influence the secondary sexual characteristics that underlie mate choice. However, comparatively little is known about their effects on animals that use coercive mating behavior. We use a tractable system consisting of monarch butterflies and their naturally occurring parasite Ophryocystis elektroscirrha to test how parasites influence host mating dynamics when males force females to copulate. Monarchs were placed in mating cages where all, half, or no individuals were experimentally infected with O. elektroscirrha. We found that parasites reduce a male's mating success such that infected males were not only less likely to copulate but obtained fewer lifetime copulations as well. This reduction in mating success was due primarily to the fact that infected males attempt to mate significantly less than uninfected males. However, we found that O. elektroscirrha did not influence male mate choice. Males chose to mate with both infected and uninfected females at similar rates, regardless of their infection status. Overall, our data highlight how mating dynamics in coercive systems are particularly vulnerable to parasites.

Automated summary

The study investigates the effects of parasites on coercive mating behavior in animals using monarch butterflies and their parasite Ophryocystis elektroscirrha as a model system. The results show that parasite infection reduces male mating success, mainly due to infected males attempting to mate less frequently. However, the parasites do not influence male mate choice. These findings highlight the vulnerability of mating dynamics in coercive systems to parasites.