The research team, led by Claudia Pérez-Calles and Jingtao Lilue, with senior authors Ashlee H. Rowe and Thomas M. Keane, built the new genomes using modern long-read sequencing and assembly approaches, producing reference-quality resources for Onychomys and its non-resistant relative. This comparative framework matters because earlier work on grasshopper mice had focused largely on a single gene family: the voltage-gated sodium channels, and in particular Nav1.8, a channel expressed in pain-sensing neurons. Previous studies had shown that structural and functional modifications of Nav1.8 in grasshopper mice block the effect of the painful toxins delivered by their scorpion prey, effectively converting a weapon of deterrence into dinner. Yet important questions remained about whether other molecular systems contribute to toxin resistance, and about how the animals respond physiologically when they are actually exposed to toxins in the wild.

By scanning the newly assembled genomes for signatures of positive selection, the researchers identified Onychomys-specific mutations in another sodium channel gene, Scn3a, which encodes the Nav1.3 channel. Unlike Nav1.8, Nav1.3 is expressed in the central nervous system and in the peripheral sensory system after nerve damage, where it is associated with heightened neuronal excitability. The discovery that grasshopper mice carry their own distinctive variants of this channel suggests that toxin resistance is not the work of a single molecular tweak but of a broader rewiring of the excitability machinery of sensory and central neurons. If Nav1.8 keeps painful toxins from firing up peripheral nociceptors, the newly identified Scn3a mutations may help ensure that any signals that do get through, or that arise from tissue damage during a scorpion battle, are blunted as well. The authors are careful to frame these as candidate adaptations whose precise functional consequences will require further experimental testing, but their recurrence in a gene so central to pain signalling makes them a compelling addition to the story.

The pangenome approach also revealed something entirely unexpected outside the nervous system: an Onychomys-specific tandem duplication of a gene called Cblif, which encodes a glycoprotein crucial for the absorption of vitamin B12 in the gut. At first glance, a vitamin transport gene seems an odd companion to toxin resistance, but the researchers connect it to the grasshopper mouse’s unusual dietary and anatomical specialisation. These rodents are carnivorous in a family dominated by seed eaters, and their stomach morphology is distinctive, characterized by an abundance of parietal cells, the acid-secreting cells of the gastric lining. The study found that Cblif is expressed in these parietal cells, and the researchers propose that the gene duplication may represent an adaptation supporting the species’ meat-rich diet and its modified stomach architecture. In an animal that consumes large quantities of arthropod prey, efficient handling of nutrients and gastric chemistry could be as important to survival as venom resistance itself, and the duplication illustrates how a pangenome can surface copy-number changes that single-reference comparisons routinely miss.

To move beyond static genome comparisons and observe the molecular response to toxin exposure as it happens, the team generated RNA sequencing data from two key sensory structures: the dorsal root ganglion, which houses the cell bodies of sensory neurons that relay pain signals from the body to the spinal cord, and the trigeminal ganglion, which performs the equivalent role for the face and head. Grasshopper mice were exposed to toxic sprays from pinacate beetles, another chemically defended prey item that these rodents subdue with gusto. The transcriptomic readout revealed that in Onychomys torridus, the southern grasshopper mouse, genes associated with transportation processes were upregulated following toxin exposure. This pattern suggests that when the animals encounter defensive chemicals, they mobilize cellular transport machinery, potentially to move toxins or their metabolites away from sensitive tissues, to shuttle protective molecules to where they are needed, or to manage the cellular stress caused by chemical assault.

Taken together, the findings sketch a multi-layered model of toxin resistance in grasshopper mice. At the first layer sit the sodium channel adaptations, with Nav1.8 modifications established by earlier work and Scn3a mutations newly identified here, that alter how pain and danger signals are generated and propagated. At the second layer sits an inducible transcriptional response, in which transport-related genes are dialled up in sensory ganglia after chemical exposure, providing a dynamic defence that complements the hard-wired channel changes. And at a third layer, the Cblif duplication hints at the digestive and metabolic specialisations that accompany a predatory lifestyle, reminding readers that adaptation to toxic prey reshapes far more than the nervous system. The authors conclude that Onychomys-specific Scn3a mutations, together with the upregulation of transport-related genes following toxin exposure, may contribute to the evolution of toxin resistance in these rodents, a formulation that is deliberately measured but nonetheless expands the known genetic substrate of the trait.

The significance of the work extends beyond one charismatic genus of desert mice. Pangenomics, the practice of building reference resources that capture the full spectrum of variation within a group of related organisms, is rapidly becoming the standard for species where a single reference genome conceals important structural differences, such as duplications, inversions and gene losses. The Onychomys study demonstrates how such resources can expose candidate adaptations that would be invisible in a conventional single-genome alignment, from tandem duplications to lineage-specific amino acid changes in physiologically critical genes. It also provides a template for studying evolutionary convergence, since toxin resistance has evolved independently in several lineages that interact with venomous prey, including other rodents, hedgehogs and opossums. Comparative work across these systems, enabled by reference-quality genomes, can help distinguish shared molecular solutions from lineage-specific innovations.

There are also potential biomedical implications. Sodium channelopathies are central to chronic pain, epilepsy and cardiac arrhythmia, and the variants that grasshopper mice have evolved under natural selection represent natural experiments in how channel function can be modified without catastrophic side effects. Understanding precisely how the Onychomys Nav1.8 and Nav1.3 variants alter channel gating, drug binding and toxin sensitivity could inform the design of new analgesics that mimic the mouse’s painlessness. Similarly, the transport genes upregulated after toxin exposure may point to endogenous detoxification and cytoprotective pathways that could be pharmacologically enhanced. The researchers caution that their results are a foundation rather than a finished edifice: functional validation, including electrophysiological characterization of the mutant channels and mechanistic dissection of the transport response, remains to be done.

For now, the grasshopper mouse has yielded another instalment of its secrets, and the picture that emerges is one of layered, genome-wide specialization. High-quality reference genomes for Onychomys species and Peromyscus eremicus now stand as public resources for the community, and the specific discoveries, from Scn3a mutations to the Cblif duplication to the toxin-induced transport response, provide a rich set of hypotheses for the next generation of experiments. What was once framed as a single-gene story about a pain-proof sodium channel has become a systems-level account of how a mammalian predator co-evolves with dangerous prey, rewiring its neurons, its digestive physiology and its stress responses in the process. As the authors and their collaborators continue to probe these adaptations, the howling little hunter of the desert may yet teach medicine a thing or two about the molecular biology of pain.

Subject of Research: Genomic adaptations underlying toxin resistance in predatory grasshopper mice (Onychomys)

Article Title: The Onychomys pangenome reveals the unique molecular adaptations that confer toxin resistance

Article References: Pérez-Calles, C., Lilue, J., Anderson, E., Haggerty, L., Martin, F. J., McCarthy, S. A., Adams, D. J., Thybert, D., Rowe, A. H., & Keane, T. M. (2026). The Onychomys pangenome reveals the unique molecular adaptations that confer toxin resistance. Genome Biology. https://doi.org/10.1186/s13059-026-04288-4

Image Credits: AI Generated

DOI: 10.1186/s13059-026-04288-4

Keywords: grasshopper mouse, Onychomys, pangenome, toxin resistance, Nav1.8, Scn3a, sodium channels, Cblif, gene duplication, scorpion venom, dorsal root ganglion, positive selection