Fluorescent Frogs, Bees' Feet-Smelling Signatures and Mites That Smite with Chemicals

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

Rate of growth as a youngster decides the sex of sea lampreys

Chromosomes are not the universal arbiters of gender. In some reptiles, it’s incubation temperature. Researchers have discovered that in sea lampreys, it’s the rate at which they grow as larva that makes them males or females when they metamorphose into parasitic bloodsucking adults.

When the fry don’t have enough plankton to eat, they grow slowly and take longer to mature. Most of the impoverished young sea lampreys become males. Fry that gorge, grow fast and reach adulthood earlier are usually females. In the US, sea lampreys are a major invasive pest of native fish species. Fisheries managers hope to use this new research in their efforts to control lamprey numbers.

Elephants are insomniacs

African elephants may sleep as little as two hours a day.  Researchers tracked the sleep patterns of two African elephant matriarchs in Chobe National Park, Botswana, by fitting an actiwatch in their trunks. A gyroscope collar told the humans if the elephants were standing or lying down. Often, elephants sleep standing up so their rapid eye movement phase is likely to suffer. They also stay awake for up to 46 hours, trekking as much as 30 kilometres in that time. No other land mammal naps for so short a time. In captivity, with no disturbance from predators or poachers, they sleep four to six hours a day.

Caption: Two recumbent bull elephants sleeping

Male nematodes mate without penis

A new species of soil nematodes has no penis. Protorhabditis hortulana, discovered in an orchard’s compost heap in the southern part of the Iberian Peninsula, eats bacteria. While other male nematodes have two genital structures called spicules, similar to a penis, the newly discovered species has none. Instead, it pumps a capsule filled with its sperm into female’s genital orifice using its cuticle. Once inside the female’s body, sperm emerge from the capsule to fertilise her eggs.

How do animals keep track of seasons?

Most animals mate, and shed and grow new coats according to season. How do they know when the time is right? In birds and mammals, the hormone melatonin, produced by the pituitary gland at night, plays the main role. The length of time that melatonin is produced controls the secretion of a protein called vascular endothelial growth factor (VEGF) by a part of the pituitary close to the brain. In summer, one form of VEGF stimulates growth of blood vessels, and in winter, another form prevents it. Researchers say the differences in VEGF allow the pituitary to communicate with the brain that directs another part of the pituitary to produce fertility hormones.

Bumblebees recognise each other by their smelly feet

A mixture of hydrocarbons produced in bumblebees’ feet sticks to flowers when they walk on them. Each can recognise its own feet odour as well as others’. This skill tells them not only if another bumblebee has visited a flower recently but who that insect was. They can differentiate between the footprints of their nest mates from those of strangers from other nests. The chemical signature of the feet scent changes over time, enabling bumblebees to assess whether a flower visited a while ago would have had time to replenish its nectar.

Caption: Bumblebees can tell the difference between the smell of other bumblebees of differing relatedness. This behaviour is demonstrated in this video through the bumblebee’s preference for one flower type (top-right & bottom-left) but avoidance of the other (top-left & bottom-right) due to the smell (scent-mark) on the flower being from bumblebees of differing relatedness. Credit: Richard Pearce

Why do guillemot chicks leap off cliffs before they can fly?

Thick-billed murres, belonging to a group of Arctic birds called guillemots, nest on narrow ledges on steep coastal cliffs. When the chicks are less than a month old, they leap hundreds of metres into the water followed by their fathers. Why do they abandon their nests when they aren’t flying fit? Were the chicks too large for their parents to feed them? Wouldn’t staying put on cliff ledges afford more protection from predators? Scientists have an explanation for this suicidal behaviour. They say it’s a toss up between safety and growth.

Chicks that took the premature leap grew twice as fast as the ones that stayed home. When their young dive to catch their own supper, their fathers don’t have to hunt and carry their meals. Guillemot fathers invest a lot more than their mates in raising their offspring. While mothers dove an hour or two daily foraging for fish, fathers spent up to six hours underwater every day. The dangers to precocious chicks were no more than those they face at the nest. Therefore, the benefits of taking the leap into sea outweighed the costs of safety at the nest.

 Caption: Guillemot chicks hurl themselves off cliff ledges. Credit: BBC Scotland

The world’s first fluorescent amphibian

The polka-dot tree frog of South America is the first amphibian that is naturally fluorescent. Many corals, fish, scorpions, and even the hawksbill sea turtle reflect long wavelength light that causes fluorescence. While researchers don’t know why other creatures give off an eerie blue, green, or red light, these DayGlo frogs can see each other’s funky colours. At dusk, when the translucent frog starts its day, it glows greenish-blue. The fluorescent molecules, called hyloins, are found in the frog’s lymph, skin, and glandular secretions. They may use it to communicate during courtship. Researchers suspect other frogs may give off similar light.

A polka-dot frog showing its fluorescent colours. Credit: Julián Faivovich and Carlos Taboada

A polka-dot frog showing its fluorescent colours. Credit: Julián Faivovich and Carlos Taboada

A mite poisons with prussic acid

Soil-living oribatid mites are not parasitic bloodsuckers. They live on decomposing plant and animal matter while some prey on nematodes. A common species, Oribatula tibialis measures half a millimetre long but is nothing to trifle with. It wages chemical warfare, producing the deadly hydrogen cyanide to ward off predators like other mites and centipedes. No other insect or spider is known to produce this toxin. How does the creature store and produce the gas without any harm to itself?

The mite’s oil glands are full of an ester, mandelonitrile hexanoate. When in danger, the mite squirts out the liquid that combines with the predator’s saliva and produces the toxic prussic acid. The colourless, almond-smelling hydrogen cyanide causes suffocation, an unpleasant experience for the predator – but causes no harm to the mite.

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.

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