The star-nosed mole (Condylura cristata) is a small semiaquatic mole found in moist, low elevation areas in the northeastern parts of North America. It is the only extant member of the tribe Condylurini and genus Condylura. It has more than 25,000 minute sensory receptors in touch organs, known as Eimer's organs, with which this hamster-sized mole feels its way around. With the help of its Eimer's organs, it may be perfectly poised to detect seismic wave vibrations.
The nose is about in diameter with its Eimer's organs distributed on 22 appendages. Eimer's organs were first described in the European mole in 1872 by German zoologist Theodor Eimer. Other mole species also possess Eimer's organs, though they are not as specialized or numerous as in the star-nosed mole. Because the star-nosed mole is functionally blind, the snout was long suspected to be used to detect electrical activity in prey animals, though little, if any, empirical support has been found for this hypothesis. The nasal star and dentition of this species appear to be primarily adapted to exploit extremely small prey. A report in the journal Nature gives this animal the title of fastest-eating mammal, taking as little as 120 milliseconds (average: 227 ms) to identify and consume individual food items. Its brain decides in approximately eight milliseconds if prey is edible or not. This speed is at the limit of the speed of neurons.
These moles are also able to smell underwater, accomplished by exhaling air bubbles onto objects or scent trails and then inhaling the bubbles to carry scents back through the nose.
Ecology and behavior The star-nosed mole lives in wet lowland areas and eats small invertebrates, such as aquatic insects (such as the larvae of caddisflies, midges, dragonflies, damselflies, crane flies, horseflies, predaceous diving beetles, and stoneflies), terrestrial insects, worms (such as earthworms, leeches, and other annelids), mollusks, and aquatic crustaceans, as well as small amphibians and small fish.Star-nosed Mole. Adirondack Ecological Center. College of Environmental Science and Forestry. State University of New York Condylura cristata has also been found in dry meadows farther away from water. They have also been found in the Great Smoky Mountains as high as . However, the star-nose mole does prefer wet, poorly drained areas and marshes. It is a good swimmer and can forage along the bottoms of streams and ponds. Like other moles, this animal digs shallow surface tunnels for foraging; often, these tunnels exit underwater. It is active day and night and remains active in winter when it has been observed tunneling through the snow and swimming in ice-covered streams. C. cristata is particularly adept at thermoregulation, maintaining a high body temperature in a wide range of external conditions relative to other Talpid moles. This explains its ability to thrive in cold aquatic environments. Little is known about the social behavior of the species, but it is suspected to be colonial.
This mole mates in late winter or early spring, and the female has one litter of typically four or five young in late spring or early summer. However, females are known to have a second litter if their first is unsuccessful. At birth, each offspring is about long, hairless, and weighs about . Their eyes, ears, and star are all sealed, opening and becoming useful only about 14 days after birth. They become independent after about 30 days and are fully mature after 10 months. Predators include the red-tailed hawk, great horned owl, barn owl, screech owl, foxes, weasels, minks, various skunks and mustelids, and large fish such as the northern pike, as well as domestic cats.
Snout comparison to visual organ Vanderbilt University neuroscientist Kenneth Catania, who has studied star-nosed moles for 20 years, recently turned his research to the study of star-moles as a route to understanding general principles about how human brains process and represent sensory information. He called star-moles "a gold mine for discoveries about brains and behavior in general—and an unending source of surprises".
Comparing the mole's snout to vision, his research showed that whenever the mole touched potential food, it made a sudden movement to position the smallest rays, the twin rays number 11, over the object for repeated rapid touches. He reports: "The similarities with vision were striking. The star movements resembled saccadic eye movements—quick movements of the eyes from one focus point to another—in their speed and time-course. The two 11th rays are over-represented in the primary somatosensory cortex relative to their size, just as the small visual fovea in primates—a small region in the center of the eye that yields the sharpest vision—is over-represented in primary visual cortex." He notes that some bats also have an auditory fovea for processing important echolocation frequencies, suggesting that "evolution has repeatedly come to the same solution for constructing a high-acuity sensory system: subdivide the sensory surface into a large, lower-resolution periphery for scanning a wide range of stimuli, and a small, high-resolution area that can be focused on objects of importance".
The star-shaped nose is a organ found only on the star-nosed mole. Living as it does, in complete darkness, the star-nosed mole relies heavily on the mechanical information of its specialized nose to find and identify their invertebrate prey without using sight (since moles have small eyes and a tiny optic nerve). This organ is often recognized by its high sensitivity and reaction speed. In only eight milliseconds it can decide whether something is edible – in fact, this is one of the fastest responses to a stimulus in the animal kingdom and is the reason why the star-nosed mole was lately recognized in the Guinness Book of World Records as the world's fastest forager.
Anatomy and physiology The star-nose is a highly specialized sensory-motor organ shaped by 22 fleshy finger-like appendages, or tendrils, that ring their nostrils and are in constant motion as the mole explores its environment. The star itself is across and thus has a diameter slightly smaller than a typical human fingertip. Nevertheless, it is much larger than the nose of other mole species, covering per touch compared to covered by the noses of other mole species. This structure is divided into a high resolution central fovea region (the central 11th pair of rays) and less sensitive peripheral areas. In this way, the star works as a "tactile eye" where the peripheral rays (1–10 on each side) study the surroundings with erratic saccade-like movements and direct the 11th ray to objects of interest, just like the primate's foveating eye.
Regardless of the anatomical position of the star as a distal (protruding or extending) portion of the nose, this is neither an olfactory structure nor an extra hand. The appendages do not contain muscles or bones and are not used to manipulate objects or capture prey. They are controlled by tendons by a complex series of muscles that are attached to the skull in order to perform a role that seems to be purely mechanical. For this purpose, the star also contains a remarkably specialized epidermis covered entirely by 25,000 small raised domes or papillae of approximately in diameter. These domes, known as Eimer's organs, are the only type of receptor organs found in the star of the star-nosed mole, which proves that the star-like structure has clearly a mechanical functioning.
Eimer's organ is a sensory structure also found in nearly all of the approximately 30 species of mole, however none contains as many as in Condylura. This large amount of specialized receptors makes the star ultrasensitive – about 6 times more sensitive than the human hand, which contains about 17,000 receptors.
Each Eimer's organ is supplied by a number of primary afferents, thus the star is densely innervated. It is associated with a Merkel cell-neurite complex at the base of the cell column, a lamellated corpuscle in the dermis just below the column and a series of free nerve endings that originate from myelinated fibers in the dermis, run through the central column and end in a ring of terminal swellings just below the outer keratinized skin surface. All 25,000 Eimer's organs distributed along the surface of the star have this basic structure in all 22 appendages. Nevertheless, the fovea region (11th pair of rays), which is shorter in area, has a lower density of these organs – 900 Eimer's organs on its surface while some of the lateral rays have over 1500. This may sound contradictory with the fact that this region has higher resolution and an important role in foraging behavior. However, instead of having more sensory organs, this fovea region uses a different approach where the skin's surface may be more sensitive to mechanoreceptic input; it has more innervation density. Rays 1 through 9 each have about 4 fibers per Eimer's organ, while rays 10 and 11 have significantly higher innervation densities of 5.6 and 7.1 fibers per organ, respectively, revealing how the sensory periphery is differentially specialized across the star.
The myelinated fibers innervating the 11 rays were photographed and counted from an enlarged photomontage by Catania and colleagues. The total number of myelinated fibers for half of the star ranged from 53,050 to 93–94; hence the total fibers for the entire star vary from roughly 106,000 to 117,000. This means that tactile information from the environment is transmitted to the somatosensory neocortex rapidly. This would be insufficient without an adequate processing system, but in the star-nosed mole, the processing also occurs at a very high speed almost approaching the upper limit at which nervous systems are capable of functioning. The threshold at which the mole can decide whether or not something is edible is of 25 milliseconds: 12 milliseconds to the neurons in the mole's somatosensory cortex to respond to touch and other 5 milliseconds for motor commands to be conducted back to the star. In comparison, this whole process takes 600 milliseconds in humans.
The importance of the star-like nose in the mole's lifestyle is evidenced in the somatosensory representation of the nose. Electrophysiological experiments using electrodes placed on the cortex during stimulation of the body demonstrated that roughly 52% of the cortex is devoted to the nose. This means that more than half of the brain is dedicated to processing sensory information acquired by this organ, even when the nose itself is only roughly 10% of the mole's actual size. Thus, it may be concluded that the nose substitutes for the eyes, with the information from it being processed so as to produce a tactile map of the environment under the mole's nose. As other mammals, the somatosensory cortex of the star-nosed mole is somatotopically organized such that sensory information from adjacent parts of the nose is processed in adjacent regions of the somatosensory cortex. Therefore, the rays are also represented in the brain. The inferior most sensitive pair of rays (11th) had a larger representation on the somatosensory cortex, even when these are the shortest pair of appendages in the nose of the star-nosed mole.