Evolution is typically portrayed as a gradual process that builds greater complexity over time. New genes are acquired, and biological systems become increasingly intricate as species adapt to their environment. However, the rise of genomic technologies has upended this conventional view. The discovery that gene loss and simplification are not just occasional events but frequent and pivotal processes in evolution offers a surprising new dimension to our understanding of biological change. This process, which might initially seem counter-intuitive—“less is more” in genetic terms—opens the door to a new evolutionary framework that highlights the unexpected advantages of gene loss, followed by gene duplication, in fostering biological innovation and survival.
This new evolutionary driver has been explored in depth in a recent article published in the journal Molecular Biology and Evolution. Led by researchers from the University of Barcelona’s Genetics Section and the Institute for Research on Biodiversity (IRBio), with collaboration from the Okinawa Institute of Science and Technology (OIST), the study introduces the concept of “less, but more”. It provides a deeper understanding of how massive gene losses followed by large-scale gene duplications can lead to significant evolutionary adaptations.
The Traditional View: Complexity Through Gene Acquisition
For much of the 20th century, evolution was often framed as a process that increased biological complexity over time. As species evolved, it was believed that they gained new genes, thus acquiring new traits that enabled them to survive in changing environments. In this view, gene duplication—where a gene is copied and potentially adapted to new functions—was recognized as an important evolutionary mechanism. However, gene loss was largely seen as a rare and often detrimental process.
This view, however, has been challenged by new findings from the genomic era. Gene loss, as it turns out, is not only common but can play a fundamental role in driving the evolution of new traits. This phenomenon is especially apparent in certain lineages, where the loss of genes results in more efficient or specialized adaptations that promote survival.
A New Evolutionary Framework: “Less, But More”
The article published in Molecular Biology and Evolution describes an important shift in our understanding of how species evolve. The authors suggest that, in many cases, gene loss can be just as important as gene acquisition. This has led to the introduction of a new framework for thinking about evolution, called “less, but more”.
The concept behind “less, but more” is that massive gene losses are often followed by gene duplications, which can significantly increase the number of genetic variations available to a species. These variations may lead to new biological functions or traits, thus providing the raw material for evolutionary innovation. The research team argues that this pattern—where simplification through gene loss is followed by expansion through gene duplication—offers an important mechanism for evolutionary change, contrary to the traditional idea that complexity must always increase.
Cristian Cañestro, the lead author of the study, explains that gene loss is a widespread phenomenon that can increase genetic variability and spark biological adaptations. Traditionally known as the “less is more” hypothesis, this phenomenon has now evolved into a broader concept that accounts for the cyclical process of gene loss followed by subsequent duplication and expansion.
Gene Loss and Duplication in the Genome of Oikopleura dioica
To explore the implications of gene loss and duplication, the research team focused on the genome of Oikopleura dioica, a species of marine zooplankton that belongs to the tunicates—a group of chordates (animals with a notochord, which includes vertebrates). The species is of particular interest because it is closely related to vertebrates but exhibits a radically different lifestyle. While vertebrates evolved into complex, highly mobile organisms, tunicates like O. dioica provide insight into the process of evolutionary change from a simpler, more static form to a more complex, active organism.
The researchers specifically focused on a family of genes known as fibroblast growth factors (FGF). These genes are essential for various developmental processes in animals, including growth, differentiation, and cellular function. By reconstructing the evolutionary history of the FGF gene family, the team was able to trace how gene loss and subsequent duplications affected the development of O. dioica and its relatives.
Gene Loss and the Evolution of FGF Families
In the case of O. dioica, the gene family underwent dramatic changes. The research revealed that the number of FGF gene families was initially reduced from eight to just two through a process of gene loss. The two remaining families, Fgf9/16/20 and Fgf11/12/13/14, each underwent duplication to produce a total of ten genes in O. dioica.
These surviving gene subfamilies, while minimal in number, are highly conserved and play critical roles in the organism’s secretory and intracellular functions. This reduction in gene number, followed by an increase through duplication, appears to have played a crucial role in shaping the biology of O. dioica. According to Gaspar Sánchez-Serna, the first author of the study, the gene loss helped establish a “minimal set” of gene families that are able to support key functions within the organism’s body.
The study also provides important insights into the way these gene changes relate to broader evolutionary processes. FGF gene duplications likely played a pivotal role in the morphological changes that allowed O. dioica to transition from a more stationary, sessile lifestyle (similar to its ascidian ancestors) to a free-living, actively swimming form. This shift is thought to be linked to important evolutionary innovations, such as the development of new body structures that facilitated mobility and the ability to interact with a more dynamic environment.
From Sessile to Active: Evolutionary Innovations in Tunicates
The transition from a sessile lifestyle to active swimming represents a dramatic shift in the evolutionary history of tunicates. The loss and duplication of FGF genes are thought to be intimately tied to this change. As the species lost certain ancestral genes, they gained new genetic potential through duplications that allowed them to evolve traits that were better suited to free-living environments.
This evolutionary shift not only led to changes in morphology but also to adaptations in developmental processes. For example, O. dioica’s ability to swim actively, rather than remain attached to the sea floor, may have been facilitated by these genetic changes, which influenced the development of its body plan and the functionality of its genes. This phenomenon offers a compelling example of how genetic reduction followed by duplication can lead to the emergence of entirely new forms of life.
Gene Duplication, Cryptic Species, and Rapid Evolution
Another important finding from this research involves the genetic differences observed in Oikopleura dioica populations from different parts of the world. These populations, despite their similar appearance, showed molecular evidence of becoming cryptic species—organisms that are genetically distinct but morphologically indistinguishable. This indicates that rapid evolutionary changes, driven by gene loss and duplication, are occurring in different populations of O. dioica, pushing them toward greater diversity despite their morphological similarities.
The study suggests that gene loss and duplication are ongoing processes that continue to shape the genetic landscape of populations, promoting diversity and adaptability. These findings underscore the importance of genetic flexibility in evolution—highlighting that sometimes, losing genes can open up new avenues for adaptive change.
Conclusion: Embracing the “Less, But More” Evolutionary Paradigm
The concept of “less, but more” revolutionizes our understanding of evolution. Rather than assuming that evolution always leads to greater genetic complexity, this new framework emphasizes the role of gene loss and duplication as central drivers of adaptive evolution. As Cañestro concludes, the idea that “losing opens up new possibilities for subsequent gains” offers a fresh perspective on how evolution can take unexpected paths toward survival and diversification.
By studying species like O. dioica, scientists can better understand how the simplification of genetic material, followed by duplication, plays a crucial role in the emergence of new adaptations and the ongoing process of evolutionary innovation. These findings are not just important for understanding the past but may also provide insights into how organisms can continue to adapt and thrive in an ever-changing world.
Reference: Gaspar Sánchez-Serna et al, Less, but More: New Insights From Appendicularians on Chordate Fgf Evolution and the Divergence of Tunicate Lifestyles, Molecular Biology and Evolution (2024). DOI: 10.1093/molbev/msae260