Journal Article

Simple versus complex models of trait evolution and stasis as a response to environmental change

Hunt, Gene, Lidgard, Scott, Hopkins, Melanie J.

2015

Overview

Significance Paleontologists have long argued about what the fossil record call tell us about how species evolve over long periods. Simple models such as stasis and random walks have been used to explore evolutionary patterns, but these have not always adequately captured the ways in which traits change over time in fossil species. Here we find that models with complex evolutionary dynamics are often favored, especially for fossil series that sample many populations, suggesting that the underlying evolutionary reality is likely more complex than represented by simplified—though still useful—models of trait change. Previous analyses of evolutionary patterns, or modes, in fossil lineages have focused overwhelmingly on three simple models: stasis, random walks, and directional evolution. Here we use likelihood methods to fit an expanded set of evolutionary models to a large compilation of ancestor–descendant series of populations from the fossil record. In addition to the standard three models, we assess more complex models with punctuations and shifts from one evolutionary mode to another. As in previous studies, we find that stasis is common in the fossil record, as is a strict version of stasis that entails no real evolutionary changes. Incidence of directional evolution is relatively low (13%), but higher than in previous studies because our analytical approach can more sensitively detect noisy trends. Complex evolutionary models are often favored, overwhelmingly so for sequences comprising many samples. This finding is consistent with evolutionary dynamics that are, in reality, more complex than any of the models we consider. Furthermore, the timing of shifts in evolutionary dynamics varies among traits measured from the same series. Finally, we use our empirical collection of evolutionary sequences and a long and highly resolved proxy for global climate to inform simulations in which traits adaptively track temperature changes over time. When realistically calibrated, we find that this simple model can reproduce important aspects of our paleontological results. We conclude that observed paleontological patterns, including the prevalence of stasis, need not be inconsistent with adaptive evolution, even in the face of unstable physical environments.

• Publisher: National Academy of Sciences
• Subject: "Earth, Atmospheric, and Planetary Sciences" / Biological Evolution / Biological Sciences / Climate change / Computer Simulation / Environment / Environmental changes / Environmental conditions / Evolution / Evolutionary biology / Fossils / Global climate / Mathematical models / Models, Biological / Oceans and Seas / Oxygen Isotopes / Paleontology / Phylogeny / Physical Sciences / Quantitative Trait, Heritable / SPECIAL FEATURE: PERSPECTIVE / Temperature