The relative brain size of birds is constantly increasing

Birds' brains relative to their body mass have grown larger as a result of evolutionary changes over the past 70 million years, according to research conducted by an international team of scientists who recently published a study of the most comprehensive and detailed family tree of bird species in the journal called Nature. An evolutionary biologist at the University of Debrecen, Tamás Székely, was also involved in the project.

This study traces the evolution of bird phylogeny from the first early birds of the dinosaur age to modern species. The phylogenetic tree was compiled by collecting whole-genome sequence data from as many as 363 bird species, representing 218 taxonomic families, which corresponds to 92 percent of all bird families. The genome data were analyzed along with anatomical features of birds, such as body mass and brain size, which are linked to behavioral and ecological traits.

The research team has found that the phylogeny reconstructed from genome data is broadly consistent with previously hypothesized phylogenies, but it has also revealed new details of the evolution of birds. A time calibration of the phylogeny using fossil evidence shows that the number of bird species as good as exploded after the mass extinction event that exterminated the dinosaurs about 66 million years ago. The main driving force for the emergence of new bird species at that time was their ability to fill the empty ecological niches that had been created after the extinction of most of the life forms on Earth.

Research findings have also shown that the body mass of bird species has decreased over time, but that there has been a rapid increase in relative brain size, which tendency continues to this day.

“The average body mass of birds has decreased during evolutionary changes, but their relative brain size has increased, indicating that they have developed cognitive abilities and probably become more intelligent,” said Tamás Székely, professor at the Institute of Biology and Ecology, Faculty of Science and Technology, UD.

According to another Hungarian researcher involved in the project, evolutionary biologist András Liker of Pannon Egyetem [University of Pannonia], the large brain size may also be linked to the evolution of complex social behavior, the impressive diversity of bird species and, in some species, sophisticated tool use.

The researchers also looked at the impact of different genome sampling methods on the accuracy of the phylogenetic tree. By analyzing one hundred and fifty thousand genomic regions, they showed that sampling both large amounts of genetic sequence and a large proportion of taxonomic diversity is important for accurately mapping the evolutionary history of the roughly 10,000 bird species alive today.

This currently available phylogenetic tree of bird families is based on the most complete pool of genetic data ever used, which has allowed a more accurate and reliable placement of several hitherto mysteriously related bird groups on the phylogenetic tree. The phylogenetic tree can serve as a solid backbone for future work on the evolutionary history of all bird species alive today, while it is also an important tool for ornithological and biodiversity research in general.

The overall research is part of the project named Bird 10 000 Genomes (B10K), one of the largest genome sequencing projects in the world, involving 52 co-authors of the paper, representing 49 institutions from 13 different countries in the world.

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Photo: Prof. Oliver Krüger
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