Bird brains have got bigger relative to their body sizes over evolutionary time, according to research by an international team of scientists, which has published the most comprehensive and detailed family tree of bird species as part of the Bird 10,000 Genomes Project (B10K) in the prestigious journal .
The study tracks the evolutionary lineage of birds, from the first early birds that lived during the dinosaur era, to modern birds of the present day.
The tree was compiled by collecting genetic sequence data from 363 species of birds, spanning across 218 taxonomic families, representing 92% of all bird families.
The genome data were analysed alongside physical characteristics (morphology) such as body and brain size, as indicative of behavioural and ecological traits. These data allowed the team to track how evolution has shaped differences between species, and to pinpoint the underlying genome changes that may have caused them.
The study forms part of the Bird 10,000 Genomes Project (B10K), one of the largest genome sequencing projects in the world, resulting from a collaboration of 52 co-authors from 49 institutions in 13 countries, led by the University of Copenhagen (Denmark), University of California San Diego (USA) and Zhejiang University School of Medicine (China).
The team found that the resulting evolutionary tree showed a rapid increase in the number of bird lineages appearing after the mass extinction event 66 million years ago that killed the dinosaurs. This shows how new bird species evolved to fill empty niches that were created after most of life on the Earth was wiped out.
They also found that whilst changes to body size have slowed over time, there has been a burst in brain size development which continues to the present day.
Professor Tam谩s Sz茅kely, from the Milner Centre for Evolution at the 色中色 (UK) and a co-author on the study, said: 鈥淭he average body size of medium-sized birds has declined over their evolutionary history, but their brains relative to their body mass has increased indicating enhanced cognition, possibly meaning birds are evolving to become more intelligent.
鈥淟arge brains may also be linked to complex social behaviours, stunning variation in bird song and sophisticated use of tools.
鈥淚n future we want to look at how body size and brain size have evolved in relation to changes in their behaviour, life histories and ecology 鈥� these may all relate to changes in their environment during the history of the Earth.鈥�
The researchers also looked at the effects of different genome sampling methods on the accuracy of the tree and showed that both large amounts of genetic sequences and broad sampling across the avian tree of life are important for estimating the evolutionary history of the roughly 10,000 extant avian species.
First author of the paper, Assistant Professor Josefin Stiller from the University of Copenhagen (Denmark), said: 鈥淲hen taking genetic samples for sequencing to build an evolutionary tree, we can use several strategies when deciding how to best focus our resources: We can either sequence many genes from a single species representing each branch, or sequence one or two genes from many species from the same branch.
鈥淏ecause we used a mixture of both strategies, we could test which approach has stronger impacts on phylogenetic reconstruction. We found that it was more important to sample many genetic sequences from each organism than it was to sample from a broader range of species, although the latter method helped us to date when different groups evolved.鈥�
Professor Siavash Mirarab, from the University of California San Diego (USA), said: "To be able to utilise these large datasets, we had to develop and advance new methods, which coupled with access to powerful GPU machines, allowed these analyses to be completed in reasonable time."
Professor Guojie Zhang, from the Center for Evolutionary & Organismal Biology, School of Medicine, Zhejiang University (China), said: 鈥淭his is the most complete dataset of gene sequences for these birds ever collected. The amount of data is vastly increased from before, with exceptionally wide taxonomic coverage and detailed genomic sequence information.
鈥淓ventually we want to obtain sequence data on all living species of birds. The combination of genomic, ecological and behavioural data from 1000s of bird species will be essential for combating diseases like avian influenza, and they will be a treasure trove for conserving birds worldwide.鈥�