Environment

Whispering Whales, Neuron-Editing Octopuses and the Mammal That Gets By on Low Oxygen

A quick review of interesting research on living things from the last month.

A mother-calf humpback whale pair in Exmouth Gulf. Credit: Fredrik Christiansen

A mother-calf humpback whale pair in Exmouth Gulf. Credit: Fredrik Christiansen

Newborn whales ‘whisper’ to their moms

Humpback whale mothers and their calves live in dread of killer whales and sexually aggressive male humpbacks seeking mating opportunities with the mothers. Hungry calves maintain radio silence. Instead, they rub against their mothers to tell them they need to nurse. This is normal behaviour for a range of cetaceans like bottlenose dolphins. However, they do need to call back and forth to each other during migrations over thousands of kilometres or diving into deeper waters. When visibility is poor, there’s a real danger that calves may separate from their mothers. But if they called loudly, they’d attract the attention of predators.

So mothers and calves turn the volume of their grunts and  squeaks low so no eavesdroppers can hear them. Their calls are 40 decibels lower than the big males, whose songs carry through the oceans for kilometres, and 20 decibels lower than normal communication between adults. The researchers raise the fear that shipping noise could interfere with this quiet communication.

Dolphins shake and toss octopuses before eating

Dolphins prepare octopuses before bolting them down. If they don’t, they can choke to death. The cephalopods cling to their predators using their sucker-lined arms and could easily block the marine mammals’ blowholes. Without arms to detach their leggy prey, dolphins leap out of the water and crash land. Even if they injure octopuses, the latter can still move their legs, and the suckers of dead ones can remain firmly fixed.

How do dolphins tackle octopuses without getting into life-threatening situations? They shake and toss them through the air. Sometimes, they grab and slam them on the water surface. Such quick violent movements batter and disorient octopuses. Once they become placid from the trauma, they become easy to swallow.

Cephalopods can edit their genetic instructions on the run

Most living creatures follow the messages issued by their genes. Based on the genetic blueprint, DNA sends messages using molecules called RNA that synthesise amino acids to build proteins. But cephalopods – octopuses, squids, and cuttlefish – edit these genetic instructions to suit their needs. They extensively edit their neurons thousands of time more than any mammal. By altering these instructions rapidly, they are better placed to adapt to changing environmental conditions.

This unorthodox behaviour comes at a price. The directives are contained in long strings of molecules. If there’s any error creeps into these strings, it cannot act on the message. So these marine organisms have ironclad DNA that isn’t amenable to mutation, and therefore their rate of evolution is much slower.

Microbes increase lifespan of the turquoise killifish

Researchers studying ageing extended the life of middle-aged turquoise killifish (Nothobranchius furzeri) by feeding them the faeces of youngsters. They first killed the gut flora of the older fish with antibiotics and dropped the excreta of young fish into their aquarium. The fish don’t eat faeces, but they investigated if the droppings were food. That sampling was enough to recolonise their guts with the microbes of younger fish. This simple act extended the life of the older fish by 40%.

Why are cockroaches prolific?

American cockroaches, ubiquitous pests in homes around the world, can lay fertile eggs without sex. Typically, the lack of a male may drives creatures to practice parthenogenesis. But female cockroaches don’t crank out eggs on a whim. Scientists may have found what triggers asexual reproduction. When female cockroaches live alone, they take their time laying eggs and their progeny die out soon. However, in groups of more than three, they detect each other’s scent. This makes them churn out eggs at a faster clip in synchronised batches. The progeny of such asexual reproduction are all females. Typically, offspring produced asexually are more likely to die compared to offspring from mated females. Simultaneous hatching may increase the survival of the nymphs.  In the lab, a colony begun with 15 female cockroaches reached a strength of more than 300 females over three years and is still going strong.

Naked mole rats act like plants when oxygen runs low

Naked mole rats: Ignore the whiskers and teeth – these are plants. Credit: Thomas Park/UIC

Naked mole rats: Ignore the whiskers and teeth – these are plants. Credit: Thomas Park/UIC

When mammals are starved of oxygen, their brain cells die. But oxygen-deprived naked mole rats can survive as long as 18 minutes without suffering any ill effects. They go into a state of suspended animation, becoming lethargic and slowing down their pulse and breathing. They release the sugars, fructose and sucrose, into their bloodstream, and the fructose is then pumped to the brain cells. In other mammals, such fructose pumps are found only in the intestines. The naked mole rats’ brain cells burn fructose anaerobically to produce energy, a trick only plants were thought to use. The animals also don’t seem to suffer from another consequence of low oxygen: pulmonary oedema, when fluid collects in the lungs.

Scientists don’t know from where the sugars are released. They think these odd-looking mammals evolved this backup plan because of the conditions in which they live. Up to 280 of them live crammed in underground burrows with little ventilation. Their habit of huddling together can deprive them of oxygen. Even when oxygen levels plummet to 20%, a toxic situation that mice can’t tolerate for longer than 15 minutes, naked mole rats can last five hours without a problem.

 

How do bioluminescent mushrooms glow?

In 1840, the Scottish botanist George Gardner discovered a species of fungus that glowed pale green in the dark, like a firefly. Native to Brazil and named after its discoverer, Neonothopanus gardneri is one of 80 luminescent species of fungi. Nearly 180 years later, scientists discovered how the mushroom produces the eerily beautiful light. Bioluminescent bacteria, snails, and fireflies emit a compound called luciferin. Lucifer means ‘light-bringer’ in Latin.

The researchers squashed mushrooms from two species – gardneri and a related species from southern Vietnam, Neonothopanus nambi – to study the structure of light-producing compounds. An enzyme called luciferase acts as a catalyst to oxidise luciferin to produce oxyluciferin. The oxidised compound is unstable and emits light as it tries to reach a more stable state. By altering the structure of luciferin, the researchers could change the colour of the light.

A couple of years ago, the researchers determined that the glow attracts insects that disperse fungal spores throughout windless forests.

Janaki Lenin is the author of My Husband and Other Animals. She lives in a forest with snake-man Rom Whitaker and tweets at @janakilenin.