A family tree for all the world’s small bird families
An international research team in which Uppsala University and the Swedish University of Agricultural Sciences (SLU) are participating has for the first time reconstructed the tree of life for all the world’s approximately 140 passerine families. The passerines include more than 6,000 species, making it the largest bird group by far. The family includes all small birds, such as chickadees, thrushes and finches as well as corvids.
The study is based on a large amount of DNA data from one to four species per family and has used these DNA sequences in combination with fossil data to estimate the age of the different branches of the tree. The tree confirms many of the relationships between the families obtained in previous studies, but it also reveals a number of new forks in branches of the tree.
One of the authors of the study is Professor Per Alström at the Department of Ecology and Genetics, Uppsala University, and the Swedish Species Information Centre, SLU. “One of the most enjoyable results for me personally is that there is now strong support for positioning the spotted wren-babbler as a ‘sister’ to several large families, such as thrushes, flycatchers, starlings and others. I was involved in ‘discovering’ the spotted wren-babbler’s unique status as a single species in a family a few years ago. Its lineage separated from its closest relatives about 25 million years ago, right after Asia was first colonised by passerines.”
The research also shows that the passerines separated from their closest relatives, parrots, about 55 million years ago and that the three main branches of passerines (New Zealand wrens, only 2 species in New Zealand; the Tyranni clade, about 1,000 species, mainly in South America; and oscines, about 5,000 species all over the world) separated about 45 million years ago from a common origin in the Australia region. From there, they have colonised the world. The Tyranni probably spread in a first round via Asia to North America and from there to South America, and much later the oscines spread in several waves all over the world.
It is hard to tell what factors affected the passerines evolution, but the results at least suggest that their divergence was not solely influenced by climate changes and colonisation of new lands. Three main groups of passerines, comprising approximately 56 per cent of all species, increased significantly in number in Australia, Africa and Eurasia beginning with the transition between the Oligocene and Miocene epochs about 23 million years ago. This could possibly be connected with the expansion of grassland and scrubland during the Miocene epoch, which may have offered new habitats in which species could evolve and have fragmented contiguous forest areas – two factors that could have favoured the evolution of new lineages.
Oliveros et al. (2019) Earth history and the passerine superradiation, PNAS: http://www.pnas.org/cgi/doi/10.1073/pnas.1813206116