Stars for their Eyes: A Nose that Acts Like a Visual System

Abstract

The star-nosed mole (Condylura cristata) is one of the most unusual mammals on the planet and stands out as an apparent biological anomaly. It is the only mammal with a “star” consisting of 22 fleshy appendages that ring the nostrils. This structure raises many questions for biologists, anatomists, and neuroscientists. What is the star for? How and why did it evolve? How does it develop? What advantages does it provide the mole? What senses are associated with the star and how is the star represented in the mole's brain? Many years of study have provided answers to these questions and revealed remarkable sensory receptors, brain specializations, and behaviors that allow star-nosed moles to flourish in their wetland habitat. The star is not an olfactory structure, but rather a touch organ with unparalleled sensitivity and resolution. The star is innervated by more than 100,000 myelinated afferents and receptive fields are often microscopic. The mole's neocortex contains visible maps of the star, which in turn reveal a somatosensory (touch) fovea paralleling the organization of primate visual cortex. These specializations allow the mole to find and eat food faster than any other mammal in terms of handling time. Developmental and comparative studies reveal a unique developmental sequence for the nasal appendages and suggest how the star evolved from less specialized ancestral species. Together these findings put the mole's star in context as an extreme adaptation, yet as a variation on more common themes and part of an anatomical continuum with other species. Finally, these studies illustrate the usefulness of diverse species for revealing general principles of brain organization, development, and evolution. Support or Funding InformationNSF grant 1456472 Star-Nosed Mole