Some of the most fundamental questions in evolution remain unanswered, such as when and how extremely diverse groups of animals – for example reptiles – first evolved. For 75 years, adaptive radiations – the relatively fast evolution of many species from a single common ancestor – have been considered as the major cause of biological diversity, including the origins of major body plans (structural and developmental characteristics that identify a group of animals) and new lineages. However, past research examining these rapid rates of evolution was largely constrained by the methods used and the amount of data available.
Postdoctoral Researcher Tiago Simões (S. Pierce Lab) teamed with Prof. Pierce and colleagues from University of Alberta to tackle the longstanding question of how adaptive radiations have shaped reptile evolution. The team examined the largest available data set of living and extinct major reptile groups (such as marine reptiles, turtles, lizards, and the ancestors of dinosaurs and crocodiles) using DNA information from modern species and hundreds of anatomical features from both modern and fossil species for statistical analysis. The study published in Nature Communications detected that periods of fast anatomical change during the origin of reptile groups often predate when those groups diversified into hundreds or thousands of species: contradicting long-held ideas of adaptive radiation in evolution biology.
“Surprisingly,” Pierce said, “reptiles that evolved similar protective armour, like turtles or serpentine bodies like snakes, show radically different rates of evolution indicating the origin and evolution of unique body plans is heterogeneous through evolution.”
“Our results also show that the origin of snakes is characterized by the fastest rates of anatomical change in the history of reptile evolution,” said Simões. “But, that this does not coincide with increases in taxonomic diversity [as predicted by adaptive radiations] or high rates of molecular evolution.”
The mismatch between morphological and molecular evolution supports the idea that protein coding DNA sequences do not seem to be correlated with broad-scale changes in anatomy. Although much more research is needed to understand how body plans evolve, the team hypothesizes that non-protein coding regions of the genome may be responsible for rapid morphological change, as these parts are more free to mutate and take on new functional roles.
“It is clear to us that to advance our understanding of the major patterns in evolution we need further studies capable of measuring phenotypic and molecular evolutionary rates, times of origin, and phenotypic diversity across such a large timescales” said Simões. EurekAlert! Harvard Gazette
Partial funding provided by the Alexander Agassiz Postdoctoral Fellowship in the Museum of Comparative Zoology at Harvard University
Image: The animals sampled in the analysis. Colors indicates rates of evolution: warm colors high rates and cool colors low rates. Courtesy of Tiago Simões