title: Hosts of avian brood parasites have evolved egg signatures with elevated information content.
abstract: Hosts of brood-parasitic birds must distinguish their own eggs from parasitic mimics, or pay the cost of mistakenly raising a foreign chick. Egg discrimination is easier when different host females of the same species each lay visually distinctive eggs (egg 'signatures'), which helps to foil mimicry by parasites. Here, we ask whether brood parasitism is associated with lower levels of correlation between different egg traits in hosts, making individual host signatures more distinctive and informative. We used entropy as an index of the potential information content encoded by nine aspects of colour, pattern and luminance of eggs of different species in two African bird families (Cisticolidae parasitized by cuckoo finches Anomalospiza imberbis, and Ploceidae by diederik cuckoos Chrysococcyx caprius). Parasitized species showed consistently higher entropy in egg traits than did related, unparasitized species. Decomposing entropy into two variation components revealed that this was mainly driven by parasitized species having lower levels of correlation between different egg traits, rather than higher overall levels of variation in each individual egg trait. This suggests that irrespective of the constraints that might operate on individual egg traits, hosts can further improve their defensive 'signatures' by arranging suites of egg traits into unpredictable combinations.
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.
authors.forename: Eleanor M
authors.initials: EM
authors.lastname: Caves
authors.affiliation: Centre for Ecology and Conservation, College of Life and Environmental Sciences, University of Exeter, Penryn Campus, Penryn, Cornwall TR10 9FE, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Stevens
authors.affiliation: Department of Statistical Science, Duke University, PO Box 90251, Durham, NC 27708-0251, USA.
authors.forename: Edwin S
authors.initials: ES
authors.lastname: Iversen
authors.affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, University of Cape Town, Cape Town, Rondebosch 7701, South Africa cns26@cam.ac.uk.
authors.forename: Claire N
authors.initials: CN
authors.lastname: Spottiswoode
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001717:Birds / Q000469:parasitology* / Q000502:physiology*; D009425:Nesting Behavior; D010063:Ovum / Q000502:physiology*; D010641:Phenotype; D020308:Songbirds / Q000469:parasitology / Q000502:physiology
keywords: avian vision; brood parasitism; coevolution; entropy; information theory; signals