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Naked Mole Rat Queen with Offspring

Naked Mole Rat Queen with Offspring

Naked Mole Rats (Heterocephalus glaber) are unique among mammals in that they are eusocial (well actually Damaraland mole rats might be eusocial too, but they are in the same family, the Bathyergidae).  Like bees or ants, mole rats live in a hive society: only one naked mole rat female is fertile and she gives birth to sterile workers who maintain and protect the underground burrows where the colony lives.  A queen breeds with 3 or 4 male naked mole rats and she jealously guards her reproductive monopoly.  If other female naked mole rats begin to produce sexual hormones or behave in a queenlike manner, the queen will viciously attack them.  When the old queen dies, violent battles can break out to become the new queen.  Once a victor emerges, the spaces between her vertebrae expand and she becomes longer and larger. Mole rats breed all year and they can produce a litter of three to twelve pups every 80 days.

Naked Mole Rat (Heterocephalus glaber)

Naked Mole Rat (Heterocephalus glaber)

Naked mole rats live in the arid parts of Kenya, Somalia, and Ethiopia.  They feed on huge tubers which weigh as much as all the mole rats in a colony.  The mole rats eat the tubers slowly from the inside, which give the roots time to regrow.  Additionally mole rats can efficiently recycle food, so newly weaned mole rats are fed feces (which can also provide sustenance for adults).    Naked mole rats have huge sharp incisors for tunneling.   Their lips close in such a way that the incisors always remain outside their mouth–so the mole rats can tunnel indefinitely without getting dirt in their mouths.   Worker mole rats are 8 to 10 cm (3 to 4 in) long and weigh 30 to 35 grams (1.1 to 1.2 oz), although the queen grows much larger.  Naked mole rats have weak eyes and tiny skinny legs.  In effect they are pale pink wrinkled tubes with a few long sensitive whisker-like hairs sprouting from their bodies.  They move equally quickly forwards and backwards through their elaborate tunnels (which can measure up to 5 kilometers (3 miles) in total length).

06_12_Digging_side

Mole rats are unusual among mammals in other significant ways as well.  Naked mole rats do not maintain same thermal homeostasis as other mammals.  Their body temperatures are much closer to the ambient temperature in their burrows.  If they become unduly cold, they move to the top tunnels of their burrows and huddle together.  If they become hot, the naked mole rats retreat into the bottom levels where the temperatures are cooler.

Oxygen is a precious commodity in the underground tunnels of mole rats, so the fossorial roents have evolved extremely efficient blood and lungs in order to maximize oxygen uptake.   Additionally mole rats have very low metabolic rates compared to other (non-hibernating) mammals.  Their hearts beat slowly:  they breathe shallowly and eat little. In times of drought or famine, they are capable of going into a survival mode where their already slow metabolisms drop another 25 percent.  Naked Mole rats lack a critical neural transmitter which would allow them to feel certain sorts of pain sensations (such as pain caused by acid or hot pepper).  It is believed that the mole rats lost the ability to feel such sensations because the high carbon dioxide levels in their tunnels lead to extremely acidic conditions (mole rats are also surprisingly acid resistant, although I shudder to think of how we know this).

naked-mole-rats

Mole rats live a long time—some captive mole rats are in their early thirties—and they do not age like other mammals but remain young and fit throughout their lives.  Additionally mole rats are untroubled by cancers.  It seems the underlying cause of this remarkable cancer-free long life is a certain hyaluronan (HMW-HA), a gooey peptide which fills up gaps between cells.  The fact that cells do not grow closely together prevents tumors from ever forming.  Hyaluronans exist in all other mammals (and in other animals).  The complex sugars are part of our joints and cartilage.  However the hyaluronan found in naked mole rats is much larger and more complicated.

Thanks to their ant-like colonial life and bizarre appearances, naked mole rats might seem quite alien, but they are near cousins to humans (primates and rodents are close relatives—which will surprise nobody who has ever known a businessperson).  They even come from the same part of Africa as us. The naked mole rats are social animals and they care deeply for one another over their decades of life.  Additionally our kinship with the wrinkly pink rats could provide other benefits.  Humans suffer greatly from aging and cancers.  Mole rats–with their remarkable hyaluronans–could provide workable insights into how to alleviate cancer and aging.

Family Portrait?

Family Portrait?

An Irisdescent Green Sweat Bee (photo by Cyrus Khamak)

Sweat bees are tiny bees of the family Halictidae.  They take their common name from their affinity for human sweat, which they lap off of our naked skin for the salts and electrolytes therein. Sweat bees are small (at least to us) and tend to measure between 3 and 10 millimeters in length. A few species have thick robust bodies, but most are slender and delicate.  They tend to be glossy black, but some have exoskeletons which are gorgeous shades of metallic gold, green, purple, or blue.

The majority of sweat bee species nest in the ground (although a few build their homes in dead trees).  The social behavior of sweat bees runs the entire gamut of bee conduct: the University of Florida Department of Entomology Website states, “species can be solitary, communal, semi-social, or eusocial.”  Sweat bees therefore greatly interest entomologists who are studying the development of eusocial insects—those hive-minded insects which form colonies made up of a mass-reproducing queen served by a number of biologically sterile individuals.  Most species of sweat bees live together in a simple underground tunnel-hive where they act more like roommates than like city-states, however some halictids do indeed create caste-based societies (albeit not as large and elaborately organized as those of honey bees or ants).

Sweat bees mass-provision their larval offspring—which is to say they stick a mass of pollen inside a waterproof cell, place an egg on it, and seal then it off until a functional adult emerges (as opposed to honey bees which lovingly feed the larva as they develop).

Halictidae species are immensely important to flowering plants.  They are critical pollinators for many wildflowers, crops, and fruits.  Therefore, although the creatures usually fly beneath our notice, they have a tremendous importance to humankind and to ecosystems as a whole. Not all sweat bees are virtuous workers: some species are cleptoparasitic and lay their eggs on the pollen masses accumulated by another species of bee.  A handful of these little bees are outright parasites in the manner of the parasitoid wasps.

A Sweat Bee Gathering Pollen and Nectar from a Poppy

Like their fiercer large relatives, sweat bees are capable of stinging, however their stings are weak (which is fortunate considering their affinity for landing on us).   Sweat bee stings rate a lowly 1.0 on the Schmidt Sting Pain Index (a remarkably poetic scale for rating the discomfort caused by hymenopteran venom). I have been stung by a sweat bee and the sensation was that of a needle-like itch which penetrated deep below the skin and then subsided almost immediately.

The sweat bees are cosmopolitan, which means they can be found throughout all similar habitats in the world (although they are thin on the ground in Australia and South East Asia).  However the sweat bees are cosmopolitan in another way: alert reader, Michael Donohue (who is always on the look-out to identify his fellow native New Yorkers), sent me an article which details the discovery and naming of a new species of Halictidae, Lasioglossum gotham, which Dr. John Ascher, a bee researcher at the American Museum of Natural History, discovered in Brooklyn Botanic garden in 2009.  In the NY Times article about the discovery, Ascher describes how New York City has a very rich diversity of wild bees.

Lasioglossum gotham–actually about the size of a rice grain (photo by American Museum of Natural History)

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