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

## TL;DR

This study explores how helminth parasites manipulate host behavior to increase transmission, finding that mature parasites reliably increase host predation risk.

## Contribution

A phylogenetic meta-analysis of 207 studies reveals patterns of host manipulation by helminths and tests ecological and evolutionary drivers.

## Key findings

- Mature parasites consistently enhance host susceptibility to predation.
- Immature parasites show little or inconsistent impact on host behavior.
- Phylogenetic constraints on host manipulation are minimal.

## 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.

Host manipulation by parasites is wide spread but the conditions shaping it remain unclear. In a phylogenetic meta‐analysis on trophically transmitted helminths, manipulation reliably increased host predation susceptibility to predation in mature parasites, while the effect of immature parasites remained unclear. No clear ecological and evolutionary drivers emerged.