Scientists have created a theoretical framework that reveals the complex role of polyploidy—when organisms have extra copies of their genomes—in the process of evolution. Their research shows that polyploidy can help maintain stable populations in consistent environments, where the need for new traits isn’t critical. This ability allows these organisms to adapt in tough conditions by enhancing the pace of evolutionary changes. This significant discovery provides new perspectives on how evolution works and its potential effects on microbiology, biotechnology, and medical science.
Evolution is fundamental to biological diversity, powered by various mechanisms that help organisms adapt and survive. One such mechanism is polyploidy, where organisms possess additional copies of their genetic material. While having extra genetic material can provide a safety net against mutations that might threaten survival, it can also hinder evolutionary advancement by overshadowing beneficial mutations. This intriguing paradox has caught the attention of researchers for many years. A recent investigation from the Earth-Life Science Institute (ELSI) at the Institute of Science Tokyo delivers new perspectives on polyploidy’s evolutionary significance. Spearheaded by ELSI’s Specially Appointed Associate Professor Tetsuhiro Hatakeyama, with assistance from co-author Associate Professor Ryudo Ohbayashi from Tokyo Metropolitan University, the study merges theoretical models with biological evidence to analyze how polyploidy impacts genetic variation and evolution. Their results indicate that polyploidy can serve as both an obstacle and a catalyst for evolutionary change, depending on the requirements for inventive adaptations in different environments.
Hatakeyama’s fascination with polyploidy originated during his early days in molecular biology while he was pursuing his master’s degree, where he conducted experiments on cyanobacteria. During that time, he pondered why these microorganisms had multiple genome copies. Although he didn’t solve that puzzle then, his subsequent research in theoretical physics, over a period of more than 15 years, led he and Ohbayashi to propose a potential answer. Hatakeyama notes, “We developed a theoretical model in the simplest way we could envision, which revealed that polyploidy slows down evolution in stable environments where gradual adaptations are necessary, yet fosters evolutionary innovation crucial for survival in extreme conditions.”
The research differentiates between smooth fitness landscapes, where changes in an organism’s traits occur gradually, and rugged landscapes, requiring major shifts in traits for survival. In smooth fitness landscapes, polyploid organisms tend to evolve more slowly due to reduced genetic variability, which makes it hard for beneficial mutations to thrive. Ohbayashi adds, “On the other hand, in rugged landscapes, polyploidy speeds up the emergence of new traits by enhancing the chances of substantial genetic changes.”
The researchers argue that two prominent theories in evolution—Fisher’s fundamental theorem of natural selection and Susumu Ohno’s concept of neofunctionalization through gene duplication—actually complement each other rather than conflict. Each of these theories is crucial depending on the necessity for rare evolutionary adjustments for survival.
A vital mechanism that contributes to faster evolution is termed “skewness,” which refers to the uneven distribution of genetic material across the extra genome copies. This enables polyploid cells to accommodate beneficial mutations in some of their genomes while maintaining overall fitness, allowing them to develop new features without jeopardizing their survival. The study makes a pioneering use of large deviation theory, which addresses rare events, to show that significant evolutionary shifts are more likely to occur in polyploid organisms and explains how biased genetic information contributes to these rare changes.
The implications of these findings are particularly relevant to the study of microbes in extreme environments, many of which exhibit polyploidy. Additionally, these insights can clarify how polyploidy presents advantages in adapting to harsh landscapes, offering important considerations for genetic engineering, industrial microbial production, resistance to drugs, and cancer treatments. This research integrates theoretical and empirical approaches for Hatakeyama, enhancing our comprehension of the role of polyploidy in evolution. “Our work sheds light on how polyploidy influences evolution and paves the way for future applications in fields like engineering and medicine,” he explains.
The study also underscores the necessity for experimental testing. Further research will be needed to verify the theoretical models, along with potential investigations into other mechanisms that contribute to evolutionary innovation. Looking forward, the researchers highlight the value of experimental approaches to confirm their findings. Hatakeyama concludes: “This research connects theoretical physics with evolutionary biology, illuminating the relationship between genetic structure and adaptability, with potential applications stretching from microorganisms to cancer cells.”
