Macroevolutionary diversification rates show time-dependency

Abstract

For centuries, biologists have been captivated by the vast disparity in species richnessbetween 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 amongst these seemingly idiosyncratic results: speciation and extinction rates follow a scaling law where 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.Significance Statement 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.Though once controversial, it is now widely accepted that both the traits of organisms and the environments in which they live can influence the pace of evolution of life on Earth (1-3) . In particular, there is tremendous variation between groups of organisms in the rate at which species form and go extinct. This variation is reflected both in the wildly uneven diversity of clades in the fossil record and in the imbalanced shape of the tree of life (2)(3)(4)(5) . Our estimates of speciation and extinction rates vary by orders of magnitude when comparing different clades, locations, or time intervals.In turn, researchers have suggested a tremendous array of mechanisms that may have accelerated or slowed the accumulation of biodiversity. These mechanisms include aspects of organisms, such as colour polymorphism (6) , body size (7) , and many others; the environment, including geographic region (8,9) , temperature (10) , and the interactions between the two (11) . Taken as a whole, this growing body of work implicates a wide variety of factors that influence speciation and/or extinction rates and suggests that the growth of the Tree of Life has been largely idiosyncratic.Despite the rapid growth of research on v...

Hybridization increases population variation during adaptive radiation

“…Adaptive radiations provide rich material for understanding how and why natural and sexual selection cause populations to diverge, how barriers to interbreeding arise, why some taxa radiate and others do not (60), and how species accumulation through speciation is reduced by extinction (61)(62)(63). Introgressive hybridization in the early stages of a radiation may play a central role in both speciation (3,4,15,64,65) or its opposite, the collapse of the speciation process (38,(66)(67)(68)(69)(70).…”

Altitudinal biodiversity patterns of seed plants along Gongga Mountain in the southeastern Qinghai–Tibetan Plateau

“…The divergence time was calibrated with 39 commonly used fossils. This phylogeny represents the current understanding about the relationships between major clades of flowering plants and has been widely used in previous studies (e.g.,Diaz, Harmon, Sugawara, Miller, & Pennell, 2019).…”

“…, which contained 32,223 flowering plant species. This phylogeny represents the current understanding about the relationships between major clades of flowering plants and has been widely used in previous studies (e.g.,Diaz, Harmon, Sugawara, Miller, & Pennell, 2019). The divergence time was calibrated with 39 commonly used fossils.…”

Do latex and resin canals spur plant diversification? Re‐examining a classic example of escape and radiate coevolution

“…A high number of sister clade comparisons in our study were relatively young and species poor (Figure ), which may confound our ability to detect diversification rate shifts. This is particularly true in light of recent evidence suggesting that diversification rates may be time‐dependent across the tree of life (Henao‐Diaz, Harmon, Sugawara, & Pennell, ). Ultimately, it may be that variation in the relationship between latex, resin and diversification rates across clades is unlikely to be explained by a single factor, or even handful of factors, and instead a myriad of clade‐specific factors may shape diversification patterns across plants (Donoghue & Sanderson, ).…”

“…A high number of sister clade comparisons in our study were relatively young and species poor (Figure 2), which may confound our ability to detect diversification rate shifts. This is particularly true in light of recent evidence suggesting that diversification rates may be time-dependent across the tree of life (Henao-Diaz, Harmon, Sugawara, & Pennell, 2018).…”