title: The evolution of reduced antagonism--A role for host-parasite coevolution.
abstract: Why do some host-parasite interactions become less antagonistic over evolutionary time? Vertical transmission can select for reduced antagonism. Vertical transmission also promotes coevolution between hosts and parasites. Therefore, we hypothesized that coevolution itself may underlie transitions to reduced antagonism. To test the coevolution hypothesis, we selected for reduced antagonism between the host Caenorhabditis elegans and its parasite Serratia marcescens. This parasite is horizontally transmitted, which allowed us to study coevolution independently of vertical transmission. After 20 generations, we observed a response to selection when coevolution was possible: reduced antagonism evolved in the copassaged treatment. Reduced antagonism, however, did not evolve when hosts or parasites were independently selected without coevolution. In addition, we found strong local adaptation for reduced antagonism between replicate host/parasite lines in the copassaged treatment. Taken together, these results strongly suggest that coevolution was critical to the rapid evolution of reduced antagonism.
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405. amakgibs@indiana.edu.
authors.forename: A K
authors.initials: AK
authors.lastname: Gibson
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405.
authors.forename: K S
authors.initials: KS
authors.lastname: Stoy
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405.
authors.forename: I A
authors.initials: IA
authors.lastname: Gelarden
authors.affiliation: Department of Biology, Emory University, Atlanta, Georgia, 30322.
authors.forename: M J
authors.initials: MJ
authors.lastname: Penley
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405.
authors.forename: C M
authors.initials: CM
authors.lastname: Lively
authors.affiliation: Department of Biology, Indiana University, Bloomington, Indiana, 47405. levi.morran@emory.edu.|Department of Biology, Emory University, Atlanta, Georgia, 30322. levi.morran@emory.edu.
authors.forename: L T
authors.initials: LT
authors.lastname: Morran
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D005075:Biological Evolution; D017173:Caenorhabditis elegans / Q000235:genetics* / Q000382:microbiology; D054884:Host-Pathogen Interactions; D012641:Selection, Genetic; D012706:Serratia marcescens / Q000235:genetics*
keywords: Caenorhabditis elegans; Serratia marcescens; evolution of virulence; experimental coevolution; experimental evolution