Richard Collins: Important to get our claws into animal subspecies

The Bengal tiger is one of nine genetically distinct tiger groups and one of five living wild.

Irish dippers and jays, isolated on this wet windy island for millennia, have developed ‘Irish solutions to Irish problems’; they are now significantly different from their cousins elsewhere, writes Richard Collins.

However, the Irish ‘races’ are not distinct enough to merit ‘species’ designation; they are deemed to be ‘subspecies’ and appropriate additions have been made to their biological names. Our dipper bears the extra title hibernicus, while the jay is lusitanicus. Such distinctions may recall the pompous titles we bestow on the great and the good.

However, animal distinctions are important; subspecies status can strengthen the case for conservation measures on a creature’s behalf. Tigers are a typical case.

Zoologists have disagreed as to how many subspecies of tiger should be recognised. Some experts will only accept two; others argue for up to six. Only 4,000 tigers remain in the wild, occupying just 7% of the species’ ancestral range. Their classification is important, therefore; each distinct race must be protected in its own right.

Tigers evolved in Asia two to three million years ago. A bottleneck in the population occurred between 72,000 and 108,000 years ago; all tigers alive today are descended from a group which survived back them. Over the millennia, populations became isolated geographically from each other. Like Irish dippers and jays, each of these developed its own peculiarities.

Writing in the journal Current Biology, Beijing-based geneticist Yue-Chen Liu and colleagues claim that disagreements over subspecies designation have hindered tiger conservation efforts. To settle the matter once and for all, her team studied the full genomes of 32 specimens from across the tiger’s range and can now offer a definitive answer to the subspecies question.

The researchers claim to have identified nine genetically distinct tiger groups. Five of these, the Bengal, Amur, Sumatran, Indochinese, and Malayan subspecies, still live wild today. A sixth one, the South China subspecies, survives only in captivity. The Caspian Bali and Javan races are, alas, extinct. Liu’s team found that, unusually for big cats, there has been very little gene flow between the various populations; each has a unique evolutionary history.

The most distinct subspecies, the Sumatran, is also the most endangered; less than 500 individuals remain in the wild. Sea levels rose during the Ice Age, cutting the Sumatrans off from their relatives elsewhere. Natural selection forced these island cats to reduce their energy demands and make do with smaller prey. 

They, and those of the South China subspecies, are the smallest tigers; males weigh 140kg at most. The Amur, or ‘Siberian’, tiger is not only the largest tiger. It’s the world’s biggest cat; one killed in Manchuria in 1943 stretched 3.5m from nose to tail and weighed almost a third of a tonne.

The South China tiger, the rarest surviving big cat, fell victim to Mao Zedong’s animal persecutions during the 1960s. Prior to the assaults of The Great Leap Forward, there were about 4,000, but none has been recorded in the wild since the early 1970s. By 1986, 40 remained in 17 Chinese zoos. In 2007, there were 72 in captivity worldwide.

Liu and her colleagues propose to carry out further research. ‘Re-wilding’ has been suggested and locations identified for possible controlled releases but attempts to return captive big cats to the wild elsewhere have been notoriously unsuccessful.

Yue-Chen Liu. Genome-wide Evolutionary Analysis of Natural History and Adaptation in the World’s Tigers. Current Biology. 2018.

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