My Second Appearance on Dom’s SketchCast

Dom invited me back on his podcast. Listen for more meandering conversation about human and animal psychology!

Buried Alive: Dwarf Lemurs Hibernate Underground

Of all the things you wouldn’t expect to find in a tropical rainforest, hibernating primates may be the cutest.

It was less than 10 years ago that scientists first discovered dwarf lemurs in western Madagascar hibernate the dry season away in hollow trees. Now, they report the hibernation habits of the island’s eastern dwarf lemurs: They spend 3 – 6 months of the year buried underground.

Fat-tailed dwarf lemur. By Frank Vassen [CC-BY-2.0 (http://creativecommons.org/licenses/by/2.0)%5D, via Wikimedia Commons

Dwarf lemurs (genus Cheirogaleus) are the only primates known to regularly hibernate. In a 2004 study, a German team reported fat-tailed dwarf lemurs (Cheirogaleus medius) in the western forests of Madagascar hibernate in tree holes for seven months of the year. They found the hibernating lemurs’ body temperature depends on how well its tree hole is insulated. In well-insulated hollows, lemurs maintained a relatively constant body temperature and woke up every 10 – 14 days for brief spells of arousal. The body temperature of lemurs in poorly insulated holes, however, fluctuated widely with the ambient temperature, and they did not go through any periods of arousal. It appears that hibernating fat-tailed lemurs regulate their temperature the reptilian way: hitching their thermostat to the environment instead of maintaining it internally. Since waking up during hibernation is energetically costly, this strategy allows them to conserve energy stores.

But why do tropical animals need to hibernate in the first place? In the western deciduous forests of Madagascar where fat-tailed lemurs live, winter temperatures can rise to over 86 °F, so it’s not a matter of cold temperatures. For western dwarf lemurs, hibernation is probably a response to the scarcity of fruit (a critical food source) and water during the winter.

Madagascar is a land with varied habitats, so eastern dwarf lemurs face different challenges. Unlike the fat-tailed lemur, eastern dwarf lemurs have to cope with (relatively) cold weather. The rainforests on the high plateaus of Madagascar are home to the island’s coldest environments. During the winter, temperatures consistently drop to nearly 40 °F and never rise above 86 °F during the day. Fruits are also scarce in eastern forests during the winter.

Non-hibernating Crossley’s dwarf lemur from Tsinjoarivo forest
Credit: K. Dausmann

A team of researchers from the Duke University Lemur Center, the University of Hamburg, and the University of Antananarivo in Madagascar set out to uncover the hibernation habits of the island’s eastern dwarf lemurs. Specifically, they looked at two species that live in Tsinjoarivo, a high-altitude rainforest in central-eastern Madagascar. Sibree’s dwarf lemur (C. sibreei) and Crossley’s dwarf lemur (C. crossleyi, also known as the furry-eared dwarf lemur) are between 7.5 and 10.5 inches long, with another 6-7 inches of tail. Sibree’s dwarf lemur is slightly smaller, weighing in at around half a pound, while Crossley’s dwarf lemur gets up to about three-quarters of a pound.

Twelve dwarf lemurs (eight C. crossleyi and four C. sibreei) were fitted with radio transmitter collars that allowed the researchers to track the animals to their hidden hibernation spots. The collars also recorded the skin temperature of their wearers every 60 minutes.

The researchers discovered both species of eastern dwarf lemur hibernated between three and six months of the year. And unlike the tree-hibernating western dwarf lemurs, the eastern dwarf lemurs all hibernated in underground burrows. The researchers found the dwarf lemurs buried 4- 16 inches below ground, beneath a spongy later of secondary roots and root hairs, humus, and leaf matter. The lemurs always hibernated individually (one lemur per burrow) and rarely changed locations over the course of hibernation season.

Close up of Crossley’s dwarf lemur from Tsinjoarivo held close to hibernaculum
Credit: M. Blanco

The underground burrows are better insulated than the tree holes used by western dwarf lemurs. The soil temperature is generally lower than the ambient temperature during the day but higher during the night. Underground hibernation might protect the lemurs from exposure to drastic temperature changes during the day and reduce the potential risk of freezing at night.

In their underground burrows, dwarf lemurs are able to maintain low, relatively constant body temperatures of about 59 °F for more than 10 days before undergoing energetically costly arousals. During the winter, the ambient temperature in high-altitude forests like Tsinjoarivo does not get high enough for the dwarf lemurs to use passive warming to raise their body temperatures. Since passive warming is not an option, maintaining a stable body temperature and avoiding mid-hibernation arousals as much as possible might be the most energetically efficient strategy to escape the challenges of winter.

In addition to the thermal advantages of hibernating underground, there may also be safety advantages. When they’re not hibernating, both Crossley’s and Sibree’s dwarf lemurs spend most of their time high in the canopy. During the non-hibernation period, the researchers observed large predatory birds flying by tree holes used by the lemurs as daytime sleeping sites and at least two dwarf lemurs were killed by such birds. While there is currently no evidence of predation of hibernating underground dwarf lemurs, not enough observations have been gathered to say with certainty whether lemurs are safer underground. The researchers report that the burrows they found were inconspicuous and may be too deep for predators to sniff out.

Given the thermal advantages of hibernating underground, why don’t western dwarf lemurs do it? The researchers believe what it might come down to is the type of soil. The soil in western Madagascar is harder and drier than the soil in eastern rainforests. Dwarf lemurs don’t have claws, so burying themselves might only be possible in spongy, soft, moist soil.

Video: Sibree’s dwarf lemur is retrieved from underground hibernaculum at Tsinjoarivo forest
Credit: J.F. Ranaivoarisoa

Reference: Blanco, M.B., Dausmann, K.H., Ranaivoarisoa, J. F. and Yoder, A.D. (2013). Underground hibernation in a primate. Scientific Reports 3: 1768. DOI: 10.1038/srep01768.

Listen To Me on Dom’s Sketch Cast!

Drawing by Dominick Rabrun

My blog recently caught the eye of Dominick Rabrun, an artist living in Silver Spring, MD. He invited me to be a guest on his podcast where he draws interesting things and has conversations with interesting people. It’s called Dom’s Sketch Cast, and you can find it here.

I had a great time talking with Dom about all sorts of cool things – vampires, naked mole rats, microbiomes, horror movies, and more. He’s a great guy and a talented artist, and hopefully I’ll have the chance to chat with him more in future Sketch Casts.

 

Profile of Erich Jarvis

I recently had the opportunity to talk with Dr. Erich Jarvis for this brief profile. He studies vocal learning, a trait which only a few animals (including humans) possess. Read the ‘Meet the Researcher’ piece: Erich Jarvis: Connecting Birdsong to Human Speech.

Beautiful New Bat Discovered in South Sudan

This is a special bat, and not just because of its strikingly beautiful spots and stripes. This is a rare specimen, whose discovery in South Sudan led researchers to identify a new genus of bat. The bat is just the fifth specimen of its kind ever collected.

The distinctly patterned bat was discovered by researchers from Bucknell University and Fauna & Flora International during a field research expedition with wildlife authorities in South Sudan.

DeeAnn Reeder, an Associate Professor of Biology at Bucknell and first author of the paper announcing the new bat genus, recognized the bat as the same species as a specimen captured in the Democratic Republic of the Congo in 1939. That specimen was classified as Glauconycteris superba, but after detailed analyses she and her colleagues determined it did not belong in the genus Glauconycteris. It was so unique that they needed to create a new genus for it.

Reeder and her colleagues named the new genus Niumbaha, which means “rare” or “unusual” in Zande, the language spoken in Western Equatoria State, where the bat was captured. The bat’s full scientific name is Niumbaha superba, reflecting both the rarity and the magnificence of this creature.

“Our discovery of this new genus of bat is an indicator of how diverse the area is and how much work remains,” Reeder said in a press release. “Understanding and conserving biodiversity is critical in many ways. Knowing what species are present in an area allows for better management. When species are lost, ecosystem-level changes ensue. I’m convinced this area is one in which we need to continue to work.”

All photos courtesy of Bucknell University/DeeAnn Reeder.

Reference: Reeder, D.M., Helgen, K.M., Vodzak, M.E., Lunde, D.P. and Ejotre, I. (2013) A new genus for a rare African vespertilionid bat: insights from South Sudan. ZooKeys 285: 89. doi: 10.3897/zookeys.285.4892

Fauna & Flora International Programme Officer Adrian Garside (left) and Bucknell University Associate Professor of Biology DeeAnn Reeder with Niumbaha superba in South Sudan.

New on Animal Minds: Monkey See, Monkey Smile

Caption: RFM during a play session between an adult (left) and a juvenile gelada (right). The juvenile mimics the adult’s full play face. Credit: P.F. Ferrari

Don’t be fooled by those impressive teeth. These two gelada monkeys (Theropithecus gelada) are making play faces at each other — the simian equivalent of sharing a laugh. It’s an example of rapid facial mimicry (RFM), a quick and involuntary mirroring of another individual’s facial expression. Previously, it had only been observed in humans and orangutans. A new study documents RFM in geladas, adding another primate species to the list of animals capable of this surprisingly sophisticated emotional exchange.

What makes RFM so special? Read the whole story at my Animal Minds blog: Monkey See, Monkey Smile.

The Secret to the Sea Hare’s Sticky Defense

An inking sea hare. (Courtesy of Genevieve Anderson)

Don’t underestimate the sea hare. It might be soft, slow, and limbless, but it makes up for all that with an arsenal of antipredatory defenses. Now, scientists have figured out how one of these defenses — a sticky, milky-white substance called opaline — deters hungry spiny lobsters. Opaline works via sensory inactivation, blocking the lobsters’ sense of smell.

Sea hares (genus Aplysia) are soft-bodied marine mollusks, closely related to sea slugs and nudibranchs. They get their common name from a pair of large sensory rhinophores, chemical receptors that project from atop their heads like bunny ears.

Because they lack a protective outer shell, sea hares are equipped with a diverse array of antipredatory defenses, including cryptic coloring and shape and a coating of toxic mucus. When attacked by a predator or manhandled by scientists, sea hares can also release a mixture of secretions from ink and opaline glands (see video at end of post). The two glands are under separate neural control and can release their secretions independently or together. Most sea hare ink is a deep purple due to pigments found in their diet of red algae. Opaline is a clear-to white liquid that becomes viscous upon contact with water, and its production and color do not depend on the sea hare’s diet.

Charles Derby, a biologist at Georgia State University, has studied what makes this ink mixture so effective against predators for nearly a decade. He and his colleagues previously discovered that spiny lobsters (Panulirus interruptus) actually find the ink secretion attractive. High levels of amino acids in the ink mimic the stimulatory properties of food, so when the lobsters encounter the secretion, they drop the sea hare and instead try to eat the ink. The ink acts as a “phagomimetic decoy,” distracting the lobsters and allowing the sea hares to make a getaway.

However, Derby and his colleagues weren’t sure how opaline fit into the picture. During these experiments, they noticed the spiny lobsters grooming their antennules (the first pair of antennae that act as their nose) when they came into contact with the opaline secretion. This suggested that it could be affecting the lobsters’ ability to taste and smell. But how? Opaline could contain chemicals that interfere with the lobster’s sensory system, or the sticky nature of the secretion could be gunking up the lobster’s receptors, giving it the equivalent of a stuffy nose. So Derby, with Tiffany Love-Chezem and Juan Aggio, decided to separate opaline’s stickiness and its chemicals and test their effects independently on spiny lobsters.

By Columbia University, New York. Gzuckier at en.wikipedia, from Wikimedia Commons

First, the researchers extracted the water-soluble portion of the sea hare’s opaline. The resulting substance had the stickiness and other physical properties of opaline, but lacked the amino acids and other chemical attractants. Then they painted the substance onto spiny lobsters’ antennules and presented them with delicious (to spiny lobsters, anyway) shrimp juice. Unlike the control lobsters with clean antennules, the lobsters with opaline-coated antennules didn’t respond to the smell of food right in front of them, and the electrical activity in their chemosensory and motor neurons was significantly reduced.

Next, the researchers tested a mixture of the most prominent amino acids found in opaline. This time, the lobsters’ neurons fired away in response to the shrimp juice. When the amino acid solution was mixed with a chemical called carboxymethylcellulose, which mimics the physical properties of opaline, neuronal firing was again inhibited. The final test, a coating of carboxymethylcellulose alone, also stopped the neurons from firing.

The scientists concluded that it’s opaline’s stickiness, rather than its component chemicals, that is responsible for blocking the lobsters’ sense of smell. Derby and his colleagues  say the experiments “provide strong support that the sensory inactivation is principally due to the secretion physically covering the antennule and thus blocking chemicals from accessing chemosensory neurons.” They suggest that with their sense of smell plugged up, the lobsters might lose their appetite or become disoriented. As they attempt to clean their antennules of the gooey coating, the sea hare makes its escape.

Video. Attack on Sea Hare by Spiny Lobster Results in the Chemosensory Organs of Spiny Lobster Becoming Coated with Sticky Ink Secretion.  The attack on a sea hare by a spiny lobster (at 5 s) causes release of the whitish opaline (at 16 s), followed the co-release of both opaline and ink (at 21 s). The subsequent close-up view of the antennules (from 31 s until the end of the video) shows the olfactory organs of the spiny lobster coated with secretion. (Courtesy of Paul M. Johnson).

 

References:

Derby, C.D. 2007. Escape by inking and secreting: marine molluscs avoid predators through a rich array of chemicals and mechanisms. Biol Bull. Dec; 213(3):274-89.

Kicklighter, C., Shabani, S., Johnson, P., and Derby, C. 2005. Sea Hares Use Novel Antipredatory Chemical Defenses. Curr. Biol. 15(6):549-554 DOI: 10.1016/j.cub.2005.01.057

Love-Chezem, T., Aggio, J. F. and Derby, C. D. 2013. Defense through sensory inactivation: sea hare ink reduces sensory and motor responses of spiny lobsters to food odors. J. Exp. Biol. 216(8):1364-1372. DOI: 10.1242/jeb.081828