The burden koalas bear
QUESTION Why can’t koalas survive without eucalyptus leaves?
EUCALYPTUS leaves are fibrous and toxic, so in order to eat them, koalas ( Phascolarctos cinereus) have developed radical and specialised physical adaptations, which has led the species down an evolutionary dead end.
The fossil pollen record shows there have been eucalyptus trees in Australia for 45 million years. They have a remarkable ability to quickly re-sprout from dormant buds after droughts or fires.
As eucalyptus became dominant, koalas developed detoxification proteins in the liver. The greater glider and ringtail possum are the only other animals known to be able to eat these poisonous leaves.
Many mammals have a fibre-digesting organ called a caecum, but the koala’s is two metres long compared to just 6cm in humans. It contains millions of bacteria that break down the fibrous leaves into substances that are easier to absorb.
Eucalyptus is lacking in nutrition, so koalas get very little energy from the effort they put into eating them. The animals have an extremely slow metabolic rate, which means they retain food in their digestive system for a long time, maximising the amount of energy and moisture extracted.
Koalas sleep between 18 and 22 hours a day, which gives them the time to digest as well as conserve energy. These unique adaptations mean they are unable to eat anything other than eucalyptus leaves.
Despite their common name, koalas are not bears, but are marsupials that split from the wombat family 35 million years ago. Their bear-like appearance is also thought to be related to their reliance on a diet of eucalyptus.
By studying skulls of koala ancestors, palaeontologists at the University of New South Wales concluded that evolution reshaped the animals’ faces to enable them to eat eucalyptus leaves while communicating over long distances.
To make the bellowing grunts that belie their cuddly appearance, koalas have an extra pair of vocal folds outside the larynx, where the oral and nasal cavities connect. It’s thought that as the
Australian climate became drier, the forests became less dense and koalas produced ever lower frequency sounds that could travel further. To hear these frequencies, they evolved round ears with an extremely large middle ear.
An elongated jaw gives them the chewing power to deal with the tough eucalyptus leaves. This combination of evolutionary quirks created their cute bear-like appearance.
Tom Davies, Gerringong, New South Wales.
QUESTION What caused the mysterious 2019 oil spill on Brazil’s beaches?
IN AUGUST 2019, large quantities of oil began to wash up along Brazil’s northeast coast, causing significant damage. More than 5,000 tonnes has been cleared up from 1,500 miles of sandy beaches.
The oil has contaminated estuaries, beaches, mangroves and reefs. Despite many theories and accusations, the source of the pollution is a mystery.
The origin of oil can be difficult to identify, but it does carry chemical fingerprints, depending on its source.
Research by the Brazilian state oil company, Petrobras, suggested it was not to blame. Chemical analysis by environmental agency Ibama agreed the spill did not match oil from the country.
Gas chromatography results have suggested the oil could be of Venezuelan origin, which has been hotly denied.
In November 2020, after analysing 826 satellite images, the Federal Police attributed the disaster to a leak suffered by Greek-flagged tanker the Bouboulina, which was carrying heavy crude oil from Venezuela to Malaysia in July 2019. But owners Delta Tankers said Bouboulina ‘completed her voyage uneventfully, without having experienced any fuel shortage’. Investigations involving other tankers plying the same route have proved inconclusive.
Dr Ken Warren, Glasgow.
QUESTION Who invented the theodolite?
THIS surveying instrument mounted on a tripod with adjustable legs is used to obtain precise angular measurements for triangulation.
English mathematician Leonard Digges is credited with the invention of the theodolite in 1550.
He was certainly the first to use the term theodolitus to describe the instrument in his book Pantometria, published by his son Thomas in 1571.
The name resembles a Greek word, but there is no obvious source for it. It’s been surmised it could come from thea meaning prospect and delo, which means make visible.
Another theory is that it is constructed from three words: itheomai, meaning see; odos for path; and litos meaning smooth or plain.
The 19th- century mathematician Professor Augustus De Morgan suggested that the word theodolite was related to alidade, a device that allows you to use the line of sight from a distant object to perform a task.
He thought it was a corruption of the Arabic word al-idhada meaning a sort of rule, but this is not widely accepted.
Another suggestion is that it was named in honour of a mathematician called Theodolus. Unfortunately, the best known Theodolus was active a century after Digges’s invention.
It took two centuries of adaptations and improvements for the theodolite to reach its final form.
The Great Theodolite invented by Jesse Ramsden in 1787 was made up of a telescope mounted on a compass, or a quadrant plus a circle and compass.
This revolutionised surveying and led to the establishment of the Ordnance Survey in 1791 to map Britain and the British Geological Survey in 1835.
Emma Lister, St Ives, Cornwall.