The Evolution and Ecology of Host Manipulation in Helminth Parasites: A Phylogenetic Meta-Analysis

Abstract

Parasites have repeatedly evolved the ability to modify their host's behaviour to enhance transmission. However, the conditions shaping such host manipulation remain unclear. I conducted a phylogenetic meta-analysis of 207 studies comprising 1635 observations from 82 parasite and 80 host taxa to identify patterns in host manipulation and test ecological and evolutionary drivers of host manipulation in trophically transmitted helminths. Manipulation reliably increased host susceptibility to predation and effects depended strongly on parasite stage: mature parasites consistently enhanced predation susceptibility, whereas immature stages showed little or inconsistent impact. In mixed infections, mature parasites dominated, and manipulation was stronger in the presence of the correct predator. Phylogenetic constraints were minimal, in line with repeated independent origins. The ecological and evolutionary drivers and constraints tested here had only weak or inconsistent effects.