Groundbreaking research on the evolutionary history of the Heliconius butterfly is the topic of three current articles involving a Mississippi State biological sciences faculty member.
Associate Professor and a Institute for Genomics, Biocomputing and Biotechnology Researcher Brian Counterman is part of a research team whose new study is featured on the November cover of “Science” shedding light on phylogenomics—the intersection of the fields of evolution and genomics—and the ability of Heliconius to split into many species within a small window of time, a topic that has made the butterflies prime research subjects for evolutionary biologists for decades. The article is available online at https://science.sciencemag.org/content/366/6465.
“For the past 30 years, MSU researchers have made strides in developing Heliconius butterflies as a model organism for studying the origin of species and evolutionary novelties,” Counterman said.
For the “Science” study, researchers used a new low-cost sequencing strategy to assemble 20 whole Heliconius genomes to reconstruct a comprehensive picture of the Heliconius diversifying process with unprecedented detail.
Their results show the “evolutionary tree” of species relationships, assumed by scientists for decades, actually looks more like an “evolutionary bush.”
“The visual representation of evolutionary relationships popularized by Darwin have been imagined like a phylogenetic tree—each species represents the tip of a tree branch and the branch represents the species’ history,” Counterman said.
“However, the ‘Science’ paper shows that species have many different histories present in their genomes marked by many branches leading to the same tips of the phylogenetic tree—a ‘bush-like’ pattern,” he said.
Counterman and colleagues “found a lot of genetic exchange after speciation, specifically in the genes that control color patterns of butterfly wings. Their wing color patterns are warning signals to potential predators that they are toxic.”
“This study supports a growing body of evidence from a variety of organisms that hybridization and the exchange of genetic material between species can be an important driver of adaptive change,” Counterman said.
For “Science,” Counterman collaborated with a team led by researchers at Harvard University, including Jim Mallet, a former faculty member in MSU’s Department of Entomology, where Mallet began his work on the genetics of Heliconius in the 1980s.
The “Science” family of journals is published by the American Association for the Advancement of Science, the world’s oldest and largest general science organization.
Counterman and his students also published their research on butterfly wing colors in a November issue of “Current Biology,” a peer-reviewed journal publishing original research spanning all areas of biology.
Jennifer L. Fenner, a doctoral student from Millport, Alabama, in MSU’s Department of Biological Sciences, co-authored with Counterman the “Current Biology” article detailing the new, cutting edge CRISPR gene-editing technology used to delete genes that influence wing color patterns—their findings demonstrate “the unpredictable complexity of evolutionary change.”
“We were surprised to find the species with mimetic color patterns did not have similar mutant color patterns,” Counterman said. “Although the genes did influence color pattern in both species, they changed the color in very different ways.”
A third article in “Proceedings of the National Academy of Sciences” and online at https://www.pnas.org/content/early/2019/11/05/1907068116 is in collaboration with a team at Cornell University and the University of Puerto Rico. Counterman and MSU graduate student Caleb Benson of Petal sought to uncover the DNA differences responsible for the rapid evolution of Heliconius wing color patterns.
The team used a combination of approaches involving genome sequencing and CRISPR-based genome editing to discover which pieces of DNA could change gene expression and butterfly wing color.
“These findings challenged our understanding of how genes are regulated during development and how novel patterns can evolve in natural populations,” Counterman said.
“Identifying how specific DNA differences can change how an organism develops and what it looks like as an adult has important implications for understanding how biodiversity is generated in nature,” Counterman said.
“Proceedings of the National Academy of Sciences” is the official journal of the National Academy of Science for the U.S., considered to be one of the most highly cited and comprehensive scientific journals that spans all fields of science.
“Publishing in all three of these highly regarded journals is tantamount to high quality scientific contributions made by the researchers at MSU,” Counterman said. “These studies build on MSU’s legacy of excellence of research in the areas of evolutionary and genomics.”
An MSU faculty member since 2010, Counterman received his Ph.D. from Duke University and has been studying the evolution and genetics of butterflies for the past 15 years.