title: Parasitism and growth in the earthworm Lumbricus terrestris: fitness costs of the gregarine parasite Monocystis sp.
abstract: Parasites inflict fitness costs on their hosts, but often the exact reduction in fitness is not well understood. We investigated the influence of infection by the gregarine genus Monocystis sp. on growth and female investment (cocoon production) of its earthworm host, Lumbricus terrestris. Earthworms (n = 81) were observed in a laboratory setting for 8 months, after which parasite load was determined. The results revealed a significant negative relationship between parasite load and growth, yet no association to cocoon production was found. Although the exact nature, strength, and evolutionary consequence of reduced growth are still unclear, the results are the first indication for a clear, albeit weak effect of Monocystis on host fitness.
authors.affiliation: Department of Evolutionary Biology, Institute of Animal Ecology and Evolution, Universität Münster, Hüfferstrasse 1, 48149 Münster, Germany. sfield@uni-muenster.de
authors.forename: S G
authors.initials: SG
authors.lastname: Field
authors.forename: N K
authors.initials: NK
authors.lastname: Michiels
mesh_terms: D000818:Animals; D016782:Apicomplexa / Q000502:physiology*; D049628:Body Size / Q000502:physiology; D005260:Female; D005298:Fertility / Q000502:physiology; D006790:Host-Parasite Interactions; D009835:Oligochaeta / Q000254:growth & development / Q000469:parasitology* / Q000502:physiology