Diversification history and morphological evolution of larks

Larks (Alaudidae) constitute one of the avian families best adapted to xeric environments, having colonized a wide suite of open habitats including deserts. Although their highest diversity is in Africa, larks occur on all non-polar continents. We tested whether larks exhibit exceptional and/or correlated shifts in the tempos of speciation and ecological trait diversification in the face of open ecological space. We employed a near-complete phylogeny and a morphological dataset including several recently recognized species. We found homogeneity in diversification dynamics across the family and evidence for a diversity-dependent slowdown in cladogenesis, which indicates that Alaudidae may approach their “ecological limit”. We did not observe an early-burst in phenotypic diversification, as would be expected in a “classic” adaptive radiation. Our findings suggest that larks’ morphology show a high level of evolutionary conservatism and overall lack ecomorphological convergence: ecological variables (diet and habitat) —which by contrast display a higher lability— explain little of shape/size variation except beak shape. Both adaptation to aridity and dietary transitions have evolved independently in multiple lineages across subfamilies. This study supports the idea that continental radiations in open habitats may reach an equilibrium faster in comparison with those in tropical forests, due to differences in ecological opportunities.