Riley Brandt, University of Calgary
Dec. 4, 2020
Evidence of parallel evolution found in tiny tooth fossils from 290 million years ago
Scientists will cite that one of the most compelling pieces of evidence for evolution is that they can often predict what adaptations an organism will develop if it’s placed in a new environment.
In practice, however, the process is too slow compared to human lifespans. As a result, we very rarely get a chance to observe these adaptations happening in our lifetimes.
Wyatt Petryshen, a graduate student supervised by Dr. Charles Henderson, PhD, in the Department of Geoscience, is the lead author of a new paper published in the journal Royal Society Proceedings B. In this study — a collaboration between the University of Calgary and the Department of Paleontology at Friedrich-Alexander University (FAU) in Erlangen, Germany — the researchers documented parallel evolution in conodonts, an extinct group of early vertebrates.
Analysis demonstrates parallel evolutionary trajectories
When it comes to evolution, cases where similar environments have led to the repeated development of the same adaptation, in organisms sharing a common ancestor, is known as parallel evolution.
The best-known examples of parallel evolution include marsupial and placental mammals, which developed nearly identical adaptations independently after they became separated on two continents millions of years ago. Direct observation of parallel evolution by humans, however, is only possible in organisms that live and reproduce fast.
One case is the rapid evolution of cichlid fishes in lakes of Nicaragua and in lakes of the east African rift. For most cases, parallel evolution can be reconstructed from changes happening over geological timescale, which can be only studied using fossils.
Conodont left behind millions of teeth-like fossils found in large abundance in marine rocks. The outstanding diversity of their forms and structures, or morphology, has made them a natural evolutionary laboratory.
In the summer of 2019, Petryshen traveled to Germany to work with Drs. Emilia Jarochowska and Kenneth De Baets at GeoZentrum Nordbayern of FAU, who have been developing methods of analyzing the morphology of fossil organisms using 3D models. The short international exchange allowed Wyatt and his co-authors to confirm that two lineages of Sweetognathus followed the same evolutionary trajectories in two different parts of the world.
Upon setting out for his exchange at FAU, Petryshen’s goal was to build on Henderson’s suggestion that the conodont Sweetognathus, which lived during the Permian Period between 299 and 284 million years ago, repeatedly evolved the same adaptations even after it moved into new and different environments. Henderson is one of only a handful of conodont researchers in the world.
This idea required years of meticulous observations under a microscope and collecting material in remote field areas ranging from Bolivia to Russia. The test for parallel evolution required scanning the microfossils in the microtomography facility of FAU, creating 3D models of each specimen, and describing their shapes mathematically.
“We were comparing the shapes between different conodont species and how they correspond to phenotype, which is the expression of genetic traits due to environment,” says Petryshen. “Based on the shape differences, you can tell the species apart. As we analyzed all the various samples, we saw the shapes changing in the same direction.”
“Wyatt has demonstrated the parallel evolution of these fossils within two lineages,” Henderson says. “We normally use the evolution of fossils to tell time, but every time we learn more about the evolution of life, we learn more about our planet. Understanding how evolution progresses represents one of the most fundamental questions in biology and paleontology.”
Funding was provided by a Discovery Grant to Henderson from the Natural Sciences and Engineering Research Council (NSERC) and travel funding to Petryshen came from the UCalgary Graduate Student Association.
The opportunity to travel, Petryshen says, was invaluable. “I had access to diverse resources and people, and experienced the cultural differences in how science is practised in Germany. Research travel is a great way for students to get a broader perspective.”