Data from: Coevolution and the diversification of nestling ornamentation in a species-rich avian radiation

Conspicuous juvenile phenotypes are puzzling to evolutionary biologists.
Why should organisms vulnerable to predation boldly broadcast their
presence? We reconstructed the evolutionary history of nestling phenotypes
across the estrildid finches (family Estrildidae) a radiation exhibiting
unparalleled diversity in nestling ornamentation. Many are parasitised by
Vidua finches whose offspring mimic host nestling phenotypes. We examined
the role of brood parasitism, predation, sibling competition and
signalling environment in the diversification of nestling ornamentation.
We found that parasitised lineages exhibit elevated rates of nestling
ornamentation evolution compared to unparasitised ones. Despite this, the
extent to which nestlings were ornamented did not differ between
parasitised and unparasitised lineages, contrasting with systems where
coevolution proceeds at the egg stage and generates increased complexity
in host traits. Species occupying denser habitats had increased
ornamentation, suggesting a role for light environment in the evolution of
begging displays. Nestling appearance showed strong phylogenetic signal,
helping explain why successfully colonised hosts are often closely related
to ancestral ones. Neither nest height nor clutch size (proxies for
predation and sibling competition) predicted nestling ornamentation
levels, and parasitism did not predict estrildid diversification rates.
Overall, our results support a model of trait diversification in which
host lead and parasites follow in the coevolutionary arms race.