Keywords
ancestor reconstruction
cowbirds
eggshell thickness
egg weight
incubation period
nestling growth
Abstract
Parasitic cowbirds lay their eggs in the nest of other species, the host, depending on the host’s parental care for their successful reproduction. It has been suggested that cowbirds modified some life-history traits as adaptations to brood parasitism. Specifically, they would have developed small-sized eggs with thicker eggshells, would have shortened their incubation periods, and would have accelerated nestling growth. A previous analysis with independent phylogenetic contrasts found that observed values of those life-history traits in parasitic cowbirds only differ from the predicted ones by their non-parasitic relatives in their thicker eggshell. In this work, we reanalyzed these traits as potential adaptations to brood parasitism in cowbirds by reconstructing ancestral values under two models of character evolution. By comparing the ancestors reconstructed from the parasitic cowbirds with those reconstructed from their non-parasitic relatives, we only found differences in eggshell thickness. This demonstrates that both techniques (ancestor reconstruction and independent phylogenetic contrasts) are consistent, and that the increase in eggshell thickness as a potential adaptation to brood parasitism is a robust result.
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