New research results from Uppsala University, Sweden, confirm the assumptions of the “dead-end” theory on maladaptation of selfing species in a fungus. This is the first time that the theory is confirmed in a haploid system, and the results were recently published in the journal Evolution.
The “dead-end” theory is one of the most important theories in evolution. It postulates that species which reproduce sexually by selfing are prone to gradual extinction due to maladaptation. The dead-end theory has been tested in model systems such as the hermaphrodite Caenorhabditis elegans, or selfing plants like Arabidopsis thaliana, but never in a haploid species – species with only a single set of chromosomes. In this study, which was conducted at Uppsala University in collaboration with the University of California Riverside, the filamentous fungus Neurospora was used.
The research teams used next-generation sequencing technologies to obtain the full genomes of four practically unstudied obligate selfing species, representing distinct transitions to selfing within the genus Neurospora. Evidence is provided that several genomic features of these species reflect maladaptation: Accelerated protein evolution rates, reduced genome defense against transposable elements, and relaxed synonymous codon usage bias. The study also shows that the spread of transposable elements and mutation rate are reduced in selfing species compared to their outcrossing counterparts.
The results, along with a previous study showing the irreversibility of transitions to selfing (Gioti A. et al, MBE 2012: 29, 3215-3226), confirm both assumptions of the dead-end theory in the model genus Neurospora and show that both sexual and asexual reproduction can have traceable impacts on the genomes of fungi.
“Our observations open new directions for future research aiming to explore mechanisms promoting long-term persistence of Neurospora and selfing species in general. The results have widespread implications for biologists studying genome evolution, sexual reproduction and evolutionary theory. Also, our approach is novel in fungi, and can inspire similar studies testing evolutionary theory in other systems where divergence/polymorphism data are available”, says lead author Anastasia Gioti, Uppsala University.
Read the full article "Neurospora and the Dead-End Hypothesis: Genomic Consequences of Selfing in the Model Genus" in the journal Evolution.
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