Many marine organisms, such as sea grasses found in the Baltic Sea, reproduce through the formation of clones. Their genetic information is a mixture of new and original genes. Credit: Dr. Jan Dierking, GEOMAR
The Kiel Evolution Center has revealed that somatic gene variations may play a greater role in evolution than previously believed.
Variability in genetic information within a species can be a key basis for different individual characteristics. It is what determines the phenotype. This includes how an individual's external shape or resistance develops. The genetic variability within a population also allows for evolutionary adaptation of a species to changing environments, for instance. Recombination, which is the process of creating new genetic information through sexual reproduction, accounts for most of the genetic variability. The genes of both the male and female individuals are split and recombined to create the offspring. This allows for almost unlimited combinations in the offspring.
This explanation of adaptability of species is not sufficient for organisms that reproduce sexually over a prolonged period of time. In the absence of recombination. Many evolutionarily-old organisms living in marine habitats that have been well-adapted to their environment (e.g. corals and sea grasses) must alter their genetic information by other means. They reproduce by creating genetically identical clones. Somatic mutations are the main way they achieve genetic variation. They are able to develop genetic variability primarily through so-called somatic mutations, which occur in tissue other than the germ line in sexual reproduction. This refers to the transformation of cells from an egg cell to a fully formed organism. However, somatic genetic variability in the body is still considered a dead end of evolution. This is because some somatic gene mutations can't be passed on to future generations. These gene changes can lead to aging or disease in more complex organisms like humans. Researchers from Kiel University's Kiel Evolution Center (KEC), and the Research Training Group, RTG) Translational Evolutionary Research at Kiel University propose a new concept of genetic variability. This view is contradicted by the previous one and focuses more heavily on somatic mutations.
Thorsten Reusch is a professor of marine ecology at GEOMAR Helmholtz Centre of Ocean Research Kiel and a member of the RTG TransEvo and KEC. He recently wrote a perspective paper in Trends in Ecology and Evolution in which he and colleagues from the U.S. and Great Britain pointed out that it is necessary to consider changes in the DNA of somatic cells in order to better understand genetic variability and how this affects evolution. This has implications for the definition and classification of an individual. If descendants of the same clone are genetically different from one another, they can attain all characteristics of biological individuality. These characteristics include metabolic independence, genetic uniqueness, and heritability.
Evolutionary adaptations can be made through genetic mosaics
The research team examined the impact of somatic genetic variation on natural selection based on genome analysis from previous research. It favors some advantageous genetic variants and the resulting traits characteristics of an organism. These are essential for adaptability and can last over the course of many generations. This is the best adaptation to the environment that an organism can make in order to survive. Many marine organisms, such as corals and sea grasses, or fungi on the land, reproduce through the formation of clones. They often go through different stages of life with different lifestyles and shapes. These modules or stages are created by budding or splitting away from an original organism. They can also occur without the need for sexual reproduction. Genetic drift can also occur within multicellular organisms, which is a key discovery. Researchers call this random variation in the frequency or certain gene variants. Because only a small number of somatic cells are required to create clonal organisms, this causes an evolutionary bottleneck. This leads to genetic variations that quickly accumulate among descendants. The natural selection process ensures that individuals with favorable genetic variations are able to adapt to changing environmental conditions and prevail despite clonal reproductive. The genetic information in modular organisms is a mix of new and original genes. This makes it possible. "Somatic gene mutations will also find their way into the reproductive cycle, affecting genetic diversity in many non-clonal species. Reusch says modular species like corals and sea grasses have more evolutionary paths than is often assumed.
Paradigm shift in evolutionary theories
Reusch and his collaborators propose a paradigm shift within evolutionary theory, which recognizes the impact of selection on modular species at multiple scales. The heart of synthetic evolution theory is sexual reproduction and its impact on population genetics. Reusch stresses that it is not appropriate to view sexual reproduction as the only basis for genetic variability. He concludes that sexual evolution is embedded in reproduction. Population genetic theory must be better integrated to allow for large numbers of clonal species including plants and fungi.
The scientists from Kiel want to investigate, among others, the effects of somatic genetic variability (SGV) on the fitness of different organisms. They also want to determine the details of the selection process. KEC's new perspective shows how fundamental research, conceptual work, and application can all be ideally enriched. The Kiel researchers are aiming to improve the theoretical and conceptual understandings of evolution in general, as well as the application of evolutionary concepts.
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More information: Thorsten B.H. Reusch et. al., Evolution via somatic gene variation in modular species. Trends in Ecology & Evolution (2021). Information from Trends in Ecology & Evolution Thorsten B.H. Reusch et. al., Evolution via somatic gene variation in modular species. (2021). DOI: 10.1016/j.tree.2021.08.011
