title: Dominant male song performance reflects current immune state in a cooperatively breeding songbird.
abstract: Conspicuous displays are thought to have evolved as signals of individual "quality", though precisely what they encode remains a focus of debate. While high quality signals may be produced by high quality individuals due to "good genes" or favourable early-life conditions, whether current immune state also impacts signalling performance remains poorly understood, particularly in social species. Here, we experimentally demonstrate that male song performance is impaired by immune system activation in the cooperatively breeding white-browed sparrow weaver (Plocepasser mahali). We experimentally activated the immune system of free-living dominant males via subcutaneous injection of phytohemagglutinin (PHA) and contrasted its effects with those of a control (phosphate buffered saline) injection. PHA-challenged males showed significant reductions in both the duration and the rate of their song performance, relative to controls, and this could not be readily attributed to effects of the challenge on body mass, as no such effects were detected. Furthermore, male song performance prior to immune-challenge predicted the scale of the inflammatory response to the challenge. Our findings suggest that song performance characteristics are impacted by current immune state. This link between current state and signal performance might therefore contribute to enforcing the honesty of signal performance characteristics. Impacts of current state on signaling may be of particular importance in social species, where subordinates may benefit from an ability to identify and subsequently challenge same-sex dominants in a weakened state.
authors.affiliation: Centre for Ecology and Conservation College of Life and Environmental Sciences University of Exeter, Penryn Campus, Treliever Road, Penryn Cornwall TR10 9EZ UK; School of Biological Sciences University of Bristol 24 Tyndall Avenue Bristol BS8 1TQ UK; Department of Zoology University of Cambridge Downing Street Cambridge CB2 3EJ UK.
authors.forename: Jenny E
authors.initials: JE
authors.lastname: York
authors.affiliation: School of Biological Sciences University of Bristol 24 Tyndall Avenue Bristol BS8 1TQ UK.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Radford
authors.affiliation: Groningen Institute for Evolutionary Life Sciences University of Groningen Nijenborgh 7 9747 AG Groningen The Netherlands.
authors.forename: Ton G
authors.initials: TG
authors.lastname: Groothuis
authors.affiliation: Centre for Ecology and Conservation College of Life and Environmental Sciences University of Exeter, Penryn Campus, Treliever Road, Penryn Cornwall TR10 9EZ UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Young
keywords: Behavioral plasticity; cooperative breeder; dominance; handicap hypothesis; resource‐allocation trade‐offs; sociality; state‐dependent signaling
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