Multidimensionality in host manipulation mimicked by

Published: 10-22-2016 In Publication

Tags: Gammarus Pulex Social Behavior

Manipulative parasites often alter the phenotype of their hosts along multiple
dimensions. ‘Multidimensionality’ in host manipulation could consist in the
simultaneous alteration of several physiological pathways independently of
one another, or proceed from the disruption of some key physiological parameter, followed by a cascade of effects. We compared multidimensionality in
‘host manipulation’ between two closely related amphipods,Gammarus fossarum
andGammarus pulex,naturally and experimentally infected withPomphorhynchus laevis(Acanthocephala), respectively. To that end, we calculated in
each host – parasite association the effect size of the difference between infected
and uninfected individuals for six different traits (activity, phototaxis, geotaxis,
attraction to conspecifics, refuge use and metabolic rate). The effects sizes were
highly correlated between host –parasite associations, providing evidence for a
relatively constant ‘infection syndrome’. Using the same methodology, we compared the extent of phenotypic alterations induced by an experimental injection
of serotonin (5-HT) in uninfectedG. pulexto that induced by experimental or
natural infection withP. laevis. We observed a significant correlation between
effect sizes across the six traits, indicating that injection with 5-HT can faithfully
mimic the ‘infection syndrome’. This is, to our knowledge, the first experimental
evidence that multidimensionality in host manipulation can proceed, at least
partly, from the disruption of some major physiological mechanism.