18. Animal Senses
Naked Mole Rats
Naked mole rats aren’t rats or moles or hairless. They are rodents. Some people consider them the ugliest creature they have ever seen — saber-tooth, poorly-made sausages. What they are is one of the most incredible creatures on earth; or I should say, under the earth. These East African rodents are about the size of mice and live in colonies up to 6 feet under the ground, in tunnel systems up to 2 1/2 miles long, with multiple branching levels. They have chambers for sleeping, food storage, and latrines. These colonies have up to 300 rodents and are eusocial; they are highly cooperative communities, and a “queen” is the sole fertile member of the colony. When a queen dies, the competition/battle for the position can take weeks, and when one is triumphant, her body length extends by a third to accommodate large litters of pups. Unlike insect eusocial colonies, the naked mole rat queens do not repress reproduction in other females with pheromones but with intimidation. They cause so much stress in other females their reproductive systems switch off. The queens do not go through menopause and can reproduce the rest of their 20-30-year lives. One queen produced over 900 pups in her life. The members of the colony care for the young, dig tunnels, gather roots, and defend and plug tunnel entrances from predators, primarily snakes. The crowded colonies cause extremely low levels of oxygen and very high levels of carbon dioxide; levels would kill or brain damage most mammals.
Their exceptionally long lives and the rarity of age-related diseases, including cancer, have stimulated considerable scientific research. Naked mole rats also develop extremely little plaque or tangles in their neurons. They are playful creatures who wrestle, play tug of war, and have some rudimentary tool use. They patch the areas of roots where they eat with dirt so that the rest of the tuber will remain healthy and grow. Their large incisors are used for digging, and their lips are behind the teeth to block earth from entering the mouth. A quarter of their muscle mass is in their jaws.
Their senses have evolved to support their success in the underground environment. Living in complete darkness, they have lost all the ability to see, except for slight changes in light and dark. They hear little in higher frequencies but some lower frequencies quite well. They are quite talkative, with around 18 vocalizations, and each colony has a distinct dialect learned in adolescence. The dialects can change when a queen dies, and a new one takes power. Taste is highly developed in naked mole rats, aiding them in foraging and avoiding poisonous plants. Used in the same endeavors, they have an acute sense of smell. The olfactory area of the brain is enlarged to support this keen sense. Smell is a primary tool in social interaction, recognizing individuals, and taking social cues. The rodents roll in their latrines to have the scent of the colony and set themselves apart from an invading mole rats from another colony. They are very xenophobic.
Naked mole rats’ most highly developed sense is touch. On each side of their body, they have about 50 whisker-like, nerve-laden vibrissae that give them full-time tactile information about their surroundings. They have more facial whiskers than many mammals to help them navigate. A fascinating tactile aspect is what they don’t feel. Adult rodents do not feel pain or not much. Their skin nerve endings have evolved to not send the expected pain level to the brain. This, again, has researchers scrambling for understanding and possible medical applications.
Naked mole rats are a good reminder of the old adage, “Don’t judge by appearances.” They may seem repellent to some, but they are critters of wonder and mystery.
Mark W McGinnis 