Why these rodents have teeth that never stop growing throughout their entire lives

Nature · Published 20 October 2026 Swipe more like this →

In short: Voles, lemmings, and muskrats are the most populous rodents in the Northern Hemisphere. To survive on abrasive plants, they evolved unique molar teeth with prismatic, alternating cusps. Because these teeth are constantly worn down by their diet, they grow continuously, ensuring these animals can feed throughout their adult lives.

The Arvicolinae subfamily, which includes voles, lemmings, and muskrats, is a major group of rodents that successfully migrated to the New World via Beringia. These animals are remarkably resilient, thriving in the subnival zone beneath winter snowpack without needing to hibernate. They are also known for extreme population fluctuations, which makes them a critical subject for paleontologists; their remains are frequently found in predator caches, such as owl pellets, and serve as essential tools for biostratigraphic dating in North America and Europe.

Beyond their unique teeth, Arvicolinae possess distinct physiological traits that set them apart from other rodents like the Muridae. A recent study comparing leukocyte profiles in wild rodents found that while both groups are dominated by lymphocytes, Arvicolinae exhibit higher neutrophil proportions. These hematological differences provide insights into their specific immune responses and physiological adaptations. Interestingly, researchers observed cells consistent with azurocytes in certain species like Microtus thomasi, highlighting the need for species-specific reference values in eco-immunological research.

The evolutionary history of the Arvicolinae is complex and has been refined through both morphological and molecular analysis. While mitochondrial DNA like the cytochrome b gene has been a standard marker, researchers now use nuclear genes like the growth hormone receptor to resolve relationships among recently evolved species. These nuclear markers are particularly useful because they evolve at a rate that avoids evolutionary noise. Recent studies have even challenged traditional classifications, such as finding that the genus Arvicola falls outside the tribe Arvicolini, demonstrating that our understanding of these rodents continues to evolve as new genetic data emerges.

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