The branching patterns of phylogenetic trees reflect evolutionary dynamics of the groups studied. Despite variation in tree patterns that result from features of organisms as well as biotic interactions and abiotic conditions, some patterns related to tree shape and branch length distribution are remarkably common across trees. Writing in Systematic Biology, Henao-Diaz and Pennell analyse nine published species-level molecular megaphylogenies to describe the major common features of these trees that characterize macroevolution. The megaphylogenies analysed include taxa such as birds, mammals and fungi that are associated with different traits, ecology and evolutionary histories. Nevertheless, the authors found marked similarities across the phylogenetic trees. The shape of the trees was similar across all taxonomic groups: trees were more imbalanced (nodes have unequal number of descendants) and exhibit more variable branch lengths towards the present. It has been suggested that taxonomic decisions (for example, which nodes on the tree to name) can influence the inferences that researchers make, as they tend to study named groups. Although the authors found no evidence that different taxonomic groups (for example, birds versus mammals) had systematically different branching patterns, the stem branches from named clades were longer than those from unnamed nodes. This suggests that higher taxonomic groups were evolutionarily distinct and conspicuous enough to be recognized as different groups and named accordingly by systematists, or that modern systematists use branch lengths (perhaps unconsciously) to make taxonomic decisions. This study reveals common patterns of macroevolution and stimulates research on the driving forces behind them.
Original reference: System. Biol., https://doi.org/10.1093/sysbio/syad032 (2023)
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