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Hosts elevate either within-clutch consistency or between-clutch distinctiveness of egg phenotypes in defence against brood parasites.

ABSTRACT: In host-parasite arms races, hosts can evolve signatures of identity to enhance the detection of parasite mimics. In theory, signatures are most effective when within-individual variation is low ('consistency'), and between-individual variation is high ('distinctiveness'). However, empirical support for positive covariation in signature consistency and distinctiveness across species is mixed. Here, we attempt to resolve this puzzle by partitioning distinctiveness according to how it is achieved: (i) greater variation within each trait, contributing to elevated 'absolute distinctiveness' or (ii) combining phenotypic traits in unpredictable combinations ('combinatorial distinctiveness'). We tested how consistency covaries with each type of distinctiveness by measuring variation in egg colour and pattern in two African bird families (Cisticolidae and Ploceidae) that experience mimetic brood parasitism. Contrary to predictions, parasitized species, but not unparasitized species, exhibited a negative relationship between consistency and combinatorial distinctiveness. Moreover, regardless of parasitism status, consistency was negatively correlated with absolute distinctiveness across species. Together, these results suggest that (i) selection from parasites acts on how traits combine rather than absolute variation in traits, (ii) consistency and distinctiveness are alternative rather than complementary elements of signatures and (iii) mechanistic constraints may explain the negative relationship between consistency and absolute distinctiveness across species.

SUBMITTER: Caves EM

PROVIDER: S-EPMC8220279 | biostudies-literature |

REPOSITORIES: biostudies-literature

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

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Project description: Not available

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Project description:Brood parasitism has evolved independently in several bird lineages, giving rise to strikingly similar behavioural adaptations that suggest convergent evolution. By comparison, convergence of physiological traits that optimize this breeding strategy has received much less attention, yet these species share many similar physiological traits that optimize this breeding strategy. Eggshell structure is important for embryonic development as it controls the flux of metabolic gases, such as O2, CO2 and H2O, into and out of the egg; in particular, water vapour conductance ( GH2O) is an essential process for optimal development of the embryo. Previous work has shown that common cuckoos ( Cuculus canorus) have a lower than expected eggshell GH2O compared with their hosts. Here, we sought to test whether this is a trait found in other independently evolved avian brood parasites, and therefore reflects a general adaptation to a parasitic lifestyle. We analysed GH2O for seven species of brood parasites from four unique lineages as well as for their hosts, and combined this with species from the literature. We found lower than expected GH2O among all our observed brood parasites both compared with hosts (except for brown-headed cowbirds ( Molothrus ater)) and compared with the expected rates given their phylogenetic positions. These findings suggest that a lowered GH2O may be a general adaptation for brood parasitism, perhaps helping the parasite nestling to develop greater aerobic fitness. This article is part of the theme issue 'The coevolutionary biology of brood parasitism: from mechanism to pattern'.

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