Genomic comparisons and the adaptive basis of brain size plasticity and chromosomal instability in the Eurasian common shrew

2026/01/08 by William R. Thomas, Tanya M Lama, Cecilia Baldoni +21 · 1 voice
Biochemistry, Genetics and Molecular Biology · Neuroscience · #Animal Vocal Communication and Behavior #Genetic diversity and population structure #Neurogenesis and neuroplasticity mechanisms

paper · doi:10.1093/molbev/msag006

openalex publication_date 2026/01/08 · openalex created_date 2026/01/11 · openalex updated_date 2026/07/30

Abstract

Sorex araneus, the Eurasian common shrew, has seasonal brain size plasticity (Dehnel's phenomenon) and many intraspecific chromosomal rearrangements. Genomic contributions to these traits, however, remain unknown. We couple a chromosome-scale genome assembly with seasonal brain transcriptomes to discover relationships between molecular evolution and both traits. While Positively Selected Genes (PSGs) enriched the Fanconi anemia DNA repair pathway (FANCI, FAAP100), which is likely involved in chromosomal rearrangements by preventing the accumulation of chromosomal aberrations, genes under positive selection or showing seasonal differential expression in the brain implicate neurogenesis (PCDHA6, SOX9, Notch signaling) and metabolic regulation (VEGFA, SPHK2) as key mechanisms underlying Dehnel's phenomenon. We also find that both positively selected and differentially expressed genes in the hippocampus are overrepresented near S. araneus evolutionary breakpoints. This relates both positive selection and differential expression to accessible chromatin configuration, suggesting that chromosomal rearrangements are integral to adaptive evolution and the regulation of brain size plasticity.

Citations

• Fertility Cost (or Sometimes a Lack of It) in Relation to Heterozygosity for Robertsonian Rearrangements in Mammals: A Review
• Captivity alters behaviour but not seasonal brain size change in semi-naturally housed shrews
• Seasonal and comparative evidence of adaptive gene expression in mammalian brain size plasticity
• Cellular development and evolution of the mammalian cerebellum
• Haplotype-resolved de novo assembly using phased assembly graphs with hifiasm
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• Merqury: reference-free quality, completeness, and phasing assessment for genome assemblies
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Discussions

• Thomas et al. reveal that positively selected and differentially expressed hippocampal genes cluster near breakpoints in shrews, tying chromosomal rearrangements and accessible chromatin to adaptation [bsky, 4 points, 1 comments]

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