How DNA Methylation Affects Evolution in Songbirds and Their Hybrids

Greg Howard
29th May, 2024

How DNA Methylation Affects Evolution in Songbirds and Their Hybrids

Image Source: Natural Science News, 2024

Key Findings

  • The study from Uppsala University focused on DNA methylation in two Ficedula flycatcher species and their hybrids on the island of Öland
  • DNA methylation differences between the two species were significant and reflected in their gene expression profiles
  • These methylation differences persisted in the F1 hybrids, indicating a role in maintaining species-specific gene expression patterns even in hybrids
Understanding how species evolve and differentiate from one another is a central question in evolutionary biology. A recent study from Uppsala University[1] delves into the role of DNA methylation—a chemical modification of DNA that can regulate gene expression—in population differentiation and speciation. This research examines the regulatory and evolutionary impact of DNA methylation in five tissues of two Ficedula flycatcher species and their naturally occurring F1 hybrids. DNA methylation typically occurs in the 5’-CpG-3’ context and can lead to differences in gene expression among genetically identical cells, which persist throughout development. These differences can reinforce gene expression variation among cells, tissues, populations, and species. Despite a surge in studies on DNA methylation, its importance in population differentiation and speciation has remained largely unexplored. This study builds on the understanding that intrinsic postzygotic isolation, which can manifest as reduced viability or fertility of interspecific hybrids, is a significant factor in speciation[2]. Such isolation often results from genetic incompatibilities between diverged parental genomes. Previous research has highlighted various mechanisms behind this phenomenon, including Dobzhansky-Muller interactions among individual genes, chromosomal rearrangements, and overall divergence of DNA sequences[2]. However, the role of epigenetic changes, such as DNA methylation, in these processes has become increasingly evident. Incompatibilities in interspecific hybrids, such as sterility and lethality, are well-documented causes of reproductive isolation and speciation[3]. These incompatibilities reveal genomic changes that occur on short evolutionary timescales and have functional consequences. While much of this divergence does not seem to be driven by ecological adaptation, it may result from responses to mutational mechanisms or internal genetic conflicts[3]. The current study by Uppsala University provides empirical evidence that DNA methylation is a critical factor in these processes. The researchers investigated DNA methylation patterns in five tissues of two species of Ficedula flycatchers and their F1 hybrids. By comparing these patterns, they aimed to understand how DNA methylation contributes to gene expression differences and, consequently, to population differentiation and speciation. The study found significant differences in DNA methylation between the two species, which were reflected in their gene expression profiles. These differences were also present in the F1 hybrids, suggesting that DNA methylation plays a role in maintaining species-specific gene expression patterns even in hybrid individuals. The findings align with previous studies that have shown the importance of regulatory genetic pathways in the evolution of postzygotic reproductive isolation[4]. These pathways can provide a source of epistatic variation, where the interaction of different genes affects the phenotype. When two populations evolve independently, their regulatory pathways can become incompatible, leading to reduced fitness in hybrids[4]. The current study adds to this understanding by demonstrating that DNA methylation is a key regulatory mechanism that can contribute to such incompatibilities. Moreover, the study's results support the notion that epigenetic changes, such as DNA methylation, can limit gene flow between diverging populations, as previously suggested[5]. In Arabidopsis thaliana, for instance, hybrid incompatibility resulting from deleterious gene combinations was shown to involve a silent epiallele, a gene that is epigenetically silenced[5]. The current study extends this concept to animal species, highlighting the broader relevance of epigenetic mechanisms in speciation. In conclusion, the research from Uppsala University provides valuable insights into the role of DNA methylation in population differentiation and speciation. By examining DNA methylation patterns in two Ficedula flycatcher species and their hybrids, the study demonstrates how epigenetic regulation can contribute to gene expression differences and reproductive isolation. These findings underscore the importance of considering epigenetic factors, alongside genetic and chromosomal changes, in the study of speciation.

GeneticsAnimal ScienceEvolution

References

Main Study

1) Regulatory and evolutionary impact of DNA methylation in two songbird species and their naturally occurring F1 hybrids

Published 29th May, 2024

https://doi.org/10.1186/s12915-024-01920-2

Related Studies

2) Mechanisms of Intrinsic Postzygotic Isolation: From Traditional Genic and Chromosomal Views to Genomic and Epigenetic Perspectives.

https://doi.org/10.1101/cshperspect.a041607

3) The genetics of hybrid incompatibilities.

https://doi.org/10.1146/annurev-genet-110410-132514

4) Rapid speciation via parallel, directional selection on regulatory genetic pathways.

Journal: Journal of theoretical biology, Issue: Vol 205, Issue 4, Aug 2000

5) Hybrid incompatibility caused by an epiallele.

https://doi.org/10.1073/pnas.1700368114


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