Asynchronous evolution of interdependent nest characters across the avian phylogeny

Abstract

Nest building is a widespread behavior among birds that reflects their adaptation to the environment and evolutionary history. However, it remains unclear how nests evolve and how their evolution relates to the bird phylogeny. Here, by examining the evolution of three nest characters-structure, site, and attachment-across all bird families, we reveal that nest characters did not change synchronically across the avian phylogeny but had disparate evolutionary trajectories. Nest structure shows stronger phylogenetic signal than nest site, while nest attachment has little variation. Nevertheless, the three characters evolved interdependently. For example, the ability of birds to explore new nest sites might depend on the emergence of novel nest structure and/or attachment. Our results also reveal labile nest characters in passerines compared with other birds. This study provides important insights into avian nest evolution and suggests potential associations between nest diversification and the adaptive radiations that generated modern bird lineages.

Fig. 1

Frequency of nest character states distributed across avian families. Proportion of avian families using the character states of a nest structure, b nest site, and c nest attachment. A filled bar indicates the proportion of avian families whose nests only have the focal character state, whereas a striped bar indicates the proportion of avian families whose nests have mixed states including the focal state

Fig. 2

Phylogenetic distribution of nest character states. Nest character state distributions and ancestral state reconstructions of a nest structure, b nest site, and c nest attachment across an avian family phylogenetic tree. The filled colors of circles at tips and nodes of the tree represent nest character states for modern families and their ancestors, respectively. A circle filled with multiple colors indicates a family or an ancestral taxon with more than one character state. The families that are brood-parasitic, build mound nests, or have no nest data were excluded from analyses as their nests cannot be characterized, although they are shown in the figures for the purpose of comprehension. The blue rings indicate two major adaptive radiations in modern bird evolution. The Roman numerals indicate events discussed in the Results. The avian order names are labeled on the tree (see Supplementary Fig. 8 for family names labeled on the tree)

Fig. 3

Phylogenetic signal tests for nest characters. Mantel coefficients under the null hypotheses in conventional Mantel (red histograms) and EM-Mantel (blue histograms) tests. a Nest structure, b nest site, and c nest attachment. Red and blue dashed lines indicate the means of the expected values in conventional Mantel and EM-Mantel tests, respectively. Green lines indicate the empirical values for the three nest characters