Gene expression and skull shape suggest seismic-sensing adaptations in blind mole rats

A comparative study of blind mole rats found higher brain expression of four genes associated with auditory perception and echolocation in other mammals, lower expression of genes linked to vision and conventional hearing, and cranial differences from surface-dwelling rats consistent with adaptation to underground acoustic conditions. Together, the findings support the hypothesis that Nannospalax xanthodon uses low-frequency sound and seismic vibration for communication and navigation, but the evidence does not establish that it practices ultrasonic echolocation.

The study combined laboratory expression measurements, comparative sequence analysis and cranial morphometry. Brain tissue was collected from eight wild N. xanthodon and eight Rattus rattus individuals from the Western Anatolia Region in Bilecik, Türkiye. The researchers measured expression of eight genes, using three replicates per animal and normalizing expression to the reference gene GAPDH. They then compared seven normalized cranial measurements from 28 adult male blind mole rats with those of 18 adult male R. rattus. Comparative coding sequences for six auditory genes were drawn from Nannospalax galili and other echolocating and non-echolocating mammals.

In the expression analysis, the blind mole rats had significantly lower levels of the vision-related genes Pax6 and Impg2 and the hearing-related genes Coch and Necap1 than the surface-dwelling rats. In contrast, Foxp2, Bmp7, Kcnq4 and Tmc1, genes associated in other species with sensorimotor coordination, cochlear organization or auditory perception, had significantly higher expression in N. xanthodon. The authors described this pattern as a possible inverse association between classical sensory systems and alternative vibration-based sensing, rather than proof of a general sensory trade-off.

Lower expression of Coch and Necap1 does not by itself demonstrate loss of hearing. The study notes that underground tunnels can filter and amplify low-frequency vibrations, potentially shifting sensory priorities away from conventional airborne sound. Blind mole rats are generally not classified as full echolocators because they specialize in low-frequency signals rather than ultrasonic calls. Their head tapping against tunnel walls has been measured at 100–200 hertz, and low frequencies of approximately 0.5–1 kHz generally propagate more effectively through underground tunnel structures.

Comparative sequence analysis identified nonsynonymous amino acid substitutions shared by N. galili and some echolocating mammals in Kcnq4, Prestin, Cdh23 and Otof. The study reported three shared sites in Kcnq4, three in Prestin, five in Cdh23 and two in Otof, with no shared changes detected in Bmp7 or Pjvk. These observations include resemblances to bats and toothed whales, but nucleotide-based phylogenetic reconstructions did not place N. galili in a shared clade with high-frequency echolocating species.

Evolutionary models further indicated predominantly purifying selection across the six genes, with overall dN/dS values from 0.017 to 0.115. Likelihood-ratio comparisons supported site-specific signals consistent with positive selection in Kcnq4, Prestin, Otof, Cdh23 and Pjvk, while Bmp7 showed no such signal. Among substitutions also shared with echolocating mammals, only position 594 of Kcnq4 had a posterior probability above 95 percent for a dN/dS ratio greater than one. The researchers therefore treated this site as a candidate for functional convergence, while cautioning that not every shared amino acid change is necessarily adaptive.

Principal component analysis of cranial measurements normalized to greatest skull length separated the skulls of N. xanthodon from those of R. rattus. The most prominent differences were associated with zygomatic arch length, braincase width and rostrum length. Wide zygomatic arches are recognized traits of fossorial mammals and may support digging, but the zygomatic region can also participate in bone conduction. Blind mole rats detect seismic signals through bone conduction, sometimes described as hearing through the jaw, so the cranial differences may reflect both excavation and acoustic functions.

The morphology cannot separate those roles with certainty. Zygomatic arches and rostrum are also influenced by fossorial demands, bite mechanics and diet, while the braincase is affected by brain size and cranial development. Expression was measured in whole brain tissue rather than the specific auditory, tactile or other tissues responsible for vibration detection. In addition, the molecular comparison used N. galili, whereas the expression and skull measurements involved N. xanthodon, and the molecular results are associations with other echolocating lineages rather than demonstrations of equivalent function.

The study therefore offers converging but bounded evidence that subterranean blind mole rats have molecular and cranial specializations relevant to low-frequency acoustic communication and seismic navigation. The authors said future work should include broader species sampling and tissue-specific studies to distinguish acoustic adaptations from the effects of digging and to clarify the evolutionary basis of alternative echolocation strategies.

Subject of Research: Molecular and cranial adaptations associated with seismic sensing in blind mole rats

Article Title: Contributions of molecular and cranial specializations for sensory adaptation in the subterranean blind mole rats ( Nannospalax xanthodon )

Article References: Gurbanov, T. Y., Gurbanov, R., Kabaoğlu, U., Tekin, B., & Baydemir, N. A. (2025). Contributions of molecular and cranial specializations for sensory adaptation in the subterranean blind mole rats (Nannospalax xanthodon). Subterranean Biology, 52, 201-226. https://doi.org/10.3897/subtbiol.52.155412

Image Credits: AI Generated

DOI: 10.3897/subtbiol.52.155412

Keywords: blind mole rats, Nannospalax xanthodon, seismic sensing, echolocation, gene expression, cranial morphometry, convergent evolution, subterranean adaptation, Contributions, molecular, cranial, specializations