Mega-evolutionary dynamics of the adaptive radiation of birds

Abstract

The origin and expansion of biological diversity is regulated by both developmental trajectories1,2 and limits on available ecological niches3–7. As lineages diversify an early, often rapid, phase of species and trait proliferation gives way to evolutionary slowdowns as new species pack into ever more densely occupied regions of ecological niche space6,8. Small clades such as Darwin’s finches demonstrate that natural selection is the driving force of adaptive radiations, but how microevolutionary processes scale up to shape the expansion of phenotypic diversity over much longer evolutionary timescales is unclear9. Here we address this problem on a global scale by analysing a novel crowd-sourced dataset of 3D-scanned bill morphology from >2000 species. We find that bill diversity expanded early in extant avian evolutionary history before transitioning to a phase dominated by morphospace packing. However, this early phenotypic diversification is decoupled from temporal variation in evolutionary rate: rates of bill evolution vary among lineages but are comparatively stable through time. We find that rare but major discontinuities in phenotype emerge from rapid increases in rate along single branches, sometimes leading to depauperate clades with unusual bill morphologies. Despite these jumps between groups, the major axes of within-group bill shape evolution are remarkably consistent across birds. We reveal that macroevolutionary processes underlying global-scale adaptive radiations support Darwinian9 and Simpsonian4 ideas of microevolution within adaptive zones and accelerated evolution between distinct adaptive peaks.

Comparative analysis of vestibular ecomorphology in birds

“…The selection of PC axes to display here is guided by our finding that relatively minor shape axes (PC11) may describe ecologically significant variation in form (and also see Cooney et al. for beak morphology).…”

Introgression and repeated co-option facilitated the recurrent emergence of C4photosynthesis among close relatives

“…2017; Cooney et al. 2017). However, species trees per se are not always able to disentangle the complex scenarios underlying the appearance or losses of multicomponent adaptations, especially when complex phenotypes are modeled as different states of a single character (e.g., Goldberg and Igic 2008; Pardo‐Diaz et al.…”

“…2017; Cooney et al. 2017). However, distinguishing between a single origin of a trait with subsequent losses versus multiple independent origins can be problematic (Whiting et al.…”

Reconstructing the geographic and climatic origins of long‐distance bird migrations

“…To base our study on the most up to date worldwide avian phylogeny, we merged two phylogenies by constructing a composite of the new phylogeny of birds recently established by Prum et al (2015) and the maximum clade credibility (MCC) tree from Jetz et al (2012), following the method described in Cooney et al (2017; see details in Supporting Information). We also pruned all trees from the Prum MCC posterior distribution to generate trees for the three study orders (i.e.…”