title: Altruism can evolve when relatedness is low: evidence from bacteria committing suicide upon phage infection.
abstract: High relatedness among interacting individuals has generally been considered a precondition for the evolution of altruism. However, kin-selection theory also predicts the evolution of altruism when relatedness is low, as long as the cost of the altruistic act is minor compared with its benefit. Here, we demonstrate evidence for a low-cost altruistic act in bacteria. We investigated Escherichia coli responding to the attack of an obligately lytic phage by committing suicide in order to prevent parasite transmission to nearby relatives. We found that bacterial suicide provides large benefits to survivors at marginal costs to committers. The cost of suicide was low, because infected cells are moribund, rapidly dying upon phage infection, such that no more opportunity for reproduction remains. As a consequence of its marginal cost, host suicide was selectively favoured even when relatedness between committers and survivors approached zero. Altogether, our findings demonstrate that low-cost suicide can evolve with ease, represents an effective host-defence strategy, and seems to be widespread among microbes. Moreover, low-cost suicide might also occur in higher organisms as exemplified by infected social insect workers leaving the colony to die in isolation.
authors.affiliation: Department of Environmental Systems Science, Institute of Integrative Biology, Swiss Federal Institute of Technology, Universitätsstrasse 16, 8092 Zürich, Switzerland. dominik.refardt@gmail.com
authors.forename: Dominik
authors.initials: D
authors.lastname: Refardt
authors.forename: Tobias
authors.initials: T
authors.lastname: Bergmiller
authors.forename: Rolf
authors.initials: R
authors.lastname: Kümmerli
mesh_terms: D000533:Altruism; D017122:Bacteriophage T4 / Q000502:physiology; D003090:Coliphages / Q000502:physiology*; D004926:Escherichia coli / Q000235:genetics / Q000502:physiology* / Q000821:virology*; D005434:Flow Cytometry; D056265:Microbial Interactions; D039002:Prophages / Q000502:physiology*; D012641:Selection, Genetic; D017361:Viral Nonstructural Proteins / Q000378:metabolism
chemical_list: C094107:RexA protein, Bacteriophage lambda; D017361:Viral Nonstructural Proteins