Macroevolutionary diversification rates show time dependency
Press
UBC Science, Mar 26, 2019 - In the Tree of Life, youth has its advantages
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A meta-analysis of phylogenetic trees and fossil time series reveals that younger groups appear to accumulate diversity at much faster rates than older groups, suggesting that there may be hidden generalities governing the diversification of life on Earth.
Significance
Some branches of the tree of life are incredibly diverse, while others are represented by only a few living species. Ultimately, this difference reflects the balance of the formation and the extinction of species. Countless explanations have been proposed for why the rates of these two processes vary between lineages, including aspects of the organisms themselves and the environments they live in. Here we reveal that a substantial amount of variation in these rates is associated with a simple factor: time. Younger groups appear to accumulate diversity at much faster rates than older groups. This time scaling of macroevolutionary rates suggests that there may be hidden generalities governing the diversification of life on Earth.
Abstract
For centuries, biologists have been captivated by the vast disparity in species richness between different groups of organisms. Variation in diversity is widely attributed to differences between groups in how fast they speciate or go extinct. Such macroevolutionary rates have been estimated for thousands of groups and have been correlated with an incredible variety of organismal traits. Here we analyze a large collection of phylogenetic trees and fossil time series and describe a hidden generality among these seemingly idiosyncratic results: speciation and extinction rates follow a scaling law in which both depend on the age of the group in which they are measured, with the fastest rates in the youngest clades. Using a series of simulations and sensitivity analyses, we demonstrate that the time dependency is unlikely to be a result of simple statistical artifacts. As such, this time scaling is likely a genuine feature of the tree of life, hinting that the dynamics of biodiversity over deep time may be driven in part by surprisingly simple and general principles.