Fig. 1: Host circadian plasticity as a target for parasitic manipulation of behavior.

A visual summary of the hypothesis that parasites manipulate host behavior by targeting their circadian plasticity, explained at three levels of biological organization: molecular, cellular and behavioral phenotypes. a The molecular clock consists of a handful of interacting core circadian genes that create robust transcription-translation feedback loops (yellow). These interactions repeat in a ~24 h rhythm and entrain many downstream genes to cycle in their expression levels (blue). The dotted circle symbolizes the surrounding environment of an organism, which contains multiple factors that can act as predictable 24 h Zeitgebers and present disturbances that require some level of clock plasticity. b Cellular and molecular mechanisms of circadian plasticity. Red boxes include examples of parasitic manipulation on both levels. Cell bodies of clock neurons (magenta) and glial cells (teal) are illustrated in an ant brain slice (adapted from⁹⁰). c Examples of rhythmic output that can be measured at the behavioral level in insects (e.g. ant, caterpillar and fly) and how these rhythms may change because of environmental factors or parasitic manipulation.