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Hosts of avian brood parasites have evolved egg signatures with elevated information content.

Caves EM, Stevens M, Iversen ES, Spottiswoode CN - Proc. Biol. Sci. (2015)

Bottom Line: 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.Parasitized species showed consistently higher entropy in egg traits than did related, unparasitized species.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.

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.

No MeSH data available.


Related in: MedlinePlus

Diversity of egg phenotypes and phylogenetic relationships within each of the two host families studied here, (a) Cisticolidae warblers and (b) Ploceidae weavers. Open and closed circles, respectively, indicate unparasitized species and species parasitized by (a) cuckoo finch and (b) diederik cuckoo in our study area in Zambia. Sample sizes (clutches) and a representative selection of eggs from five clutches are shown for each species.
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RSPB20150598F1: Diversity of egg phenotypes and phylogenetic relationships within each of the two host families studied here, (a) Cisticolidae warblers and (b) Ploceidae weavers. Open and closed circles, respectively, indicate unparasitized species and species parasitized by (a) cuckoo finch and (b) diederik cuckoo in our study area in Zambia. Sample sizes (clutches) and a representative selection of eggs from five clutches are shown for each species.

Mentions: In support of this hypothesis, recent studies have revealed low levels of correlation among egg traits in hosts of the cuckoo finch Anomalospiza imberbis [11,19] and common cuckoo Cuculus canorus [23], potentially increasing the information about egg identity that they encode. However, neither study was able to compare these low levels of correlation to baseline levels in related, unparasitized host species. Hence, they could not specifically test whether low levels of correlation are an adaptation to parasitism. In this study, we took a comparative approach to examine sympatric parasitized and unparasitized species within two African bird families, warblers (Cisticolidae) and weavers (Ploceidae). Each family is heavily parasitized by mimetic parasites (cuckoo finches [24] and diederik cuckoos Chrysococcyx caprius [25], respectively), and each shows remarkable diversity in egg phenotype within and between species (figure 1). We quantified multiple egg traits (colour, luminance and several aspects of pattern) using established visual modelling approaches and metrics that have in past work predicted rejection behaviour by three warbler host species at the same study site [11,19]. Hence, this approach captures information used by hosts themselves in distinguishing their own eggs from those of parasites.FigureĀ 1.


Hosts of avian brood parasites have evolved egg signatures with elevated information content.

Caves EM, Stevens M, Iversen ES, Spottiswoode CN - Proc. Biol. Sci. (2015)

Diversity of egg phenotypes and phylogenetic relationships within each of the two host families studied here, (a) Cisticolidae warblers and (b) Ploceidae weavers. Open and closed circles, respectively, indicate unparasitized species and species parasitized by (a) cuckoo finch and (b) diederik cuckoo in our study area in Zambia. Sample sizes (clutches) and a representative selection of eggs from five clutches are shown for each species.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4590476&req=5

RSPB20150598F1: Diversity of egg phenotypes and phylogenetic relationships within each of the two host families studied here, (a) Cisticolidae warblers and (b) Ploceidae weavers. Open and closed circles, respectively, indicate unparasitized species and species parasitized by (a) cuckoo finch and (b) diederik cuckoo in our study area in Zambia. Sample sizes (clutches) and a representative selection of eggs from five clutches are shown for each species.
Mentions: In support of this hypothesis, recent studies have revealed low levels of correlation among egg traits in hosts of the cuckoo finch Anomalospiza imberbis [11,19] and common cuckoo Cuculus canorus [23], potentially increasing the information about egg identity that they encode. However, neither study was able to compare these low levels of correlation to baseline levels in related, unparasitized host species. Hence, they could not specifically test whether low levels of correlation are an adaptation to parasitism. In this study, we took a comparative approach to examine sympatric parasitized and unparasitized species within two African bird families, warblers (Cisticolidae) and weavers (Ploceidae). Each family is heavily parasitized by mimetic parasites (cuckoo finches [24] and diederik cuckoos Chrysococcyx caprius [25], respectively), and each shows remarkable diversity in egg phenotype within and between species (figure 1). We quantified multiple egg traits (colour, luminance and several aspects of pattern) using established visual modelling approaches and metrics that have in past work predicted rejection behaviour by three warbler host species at the same study site [11,19]. Hence, this approach captures information used by hosts themselves in distinguishing their own eggs from those of parasites.FigureĀ 1.

Bottom Line: 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.Parasitized species showed consistently higher entropy in egg traits than did related, unparasitized species.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK.

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.

No MeSH data available.


Related in: MedlinePlus