“Another misconception is that there is only one locus of selection,” Lang explains. “Mmulti-level selection, as the name suggests, asserts that selection can act simultaneously on multiple levels of biological organization.“
In this experiment, selection at multiple levels was common, Lang said. “Selection acts on several levels of biological organization, from the genes of a cell to the individuals of a population. Selection at one level can impact fitness at another.
“In reality, when we extended our study of the evolution of the host virus genome to other populations, we found that almost half of the 140 or so populations we studied underwent multi-level selection, fixing adaptive mutations in nuclear and viral genomes,” he adds.
“Evolutionary laboratory experiments have proven to be very effective in studying the principles of evolution, but this work is the first to document a non-transitive interaction and provide a mechanistic explanation,” says co-author Sean. W. Buskirk, an assistant professor at West Chester University who collaborated on research as a postdoctoral student in Lang’s lab. “Ultimately, the presence of a virus in the ancestor has a huge impact on how evolved yeast populations compete and interact with one another.”
The work of co-author Alecia B. Rokes, then an undergraduate biology student at Lehigh, focused on the competition of two intracellular viruses inside yeast cells in what she calls her own. “Virus club”.
“I worked on two competing viruses within yeast cells to see if one of the viral variants had an advantage over the other, resulting in a higher frequency and one virus supplanting the other,” says Rokes, now a graduate student in microbiology at the University of Pittsburgh. “It was amazing to be part of the process of elimination, persistence and sheer curiosity to understand what was really going on in these populations.”
By showing that non-transitive interactions can occur along a line of genealogical succession, the team’s work has broad implications for the understanding of evolutionary processes by the scientific community.
“This resolves what evolutionary biologist Stephen Jay Gould has called” the first-level paradox, “which is the inability to identify broad patterns of progress over long evolutionary timescales, despite clear evidence of active selection. over successive short intervals of time, ”Lang says. “In addition, it calls into question the existence of true fitness maxima and, more broadly, it implies that directionality and evolutionary progress mcan be illusory.