Blind, Cave-Dwelling Remipedes Are the Closest Living Relatives of Insects
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Small wonders It’s not humans that dominate the world, finds James O’Donoghue BJÖRN VON REUMONT is in search of an Three-quarters of all known animals are This hickory horned devil embodies one the The clincher came a year ago. “Scientists had have helped, but it still probably took millions oddity. The creature, a blind crustacean, insects, a staggering 1 million species in total greatest insect innovations – metamorphosis been debating insect relationships for more of years for truly terrestrial insects to evolve. 4 centimetres long and resembling an upside with an estimated 4 to 5 million yet to be than 200 years. It was clear that a new Indeed, some of the most primitive species “ Blind, cave-dwelling down centipede, is to be found in the watery discovered. By contrast, there are fewer than emerging in the Cambrian period, between approach was needed,” says Bernhard Misof of alive today, the jumping bristletails, still need remipedes are depths of just a few sinkhole caves around 70,000 vertebrate species. Harvard University 550 and 500 million years ago. The oldest insect the Alexander Koenig Research Museum in moist soil to live in. But the land offered big the world – which is why von Reumont is in entomologist Edward O. Wilson has suggested fossil is some 410 million years old, but it’s an Bonn, Germany. So he and a team of more opportunities too. There was plenty to eat and the closest living the ancient Mayan rainforest of the Yucatan there may be as many as 10 quintillion insects elaborate creature, indicating that insects than 100 researchers carried out a huge there were fewer predators to deal with than in in Mexico. alive at any one time – that’s 1018, or more than evolved much earlier. Their ancestors were genetic study of insect evolution and the sea. Misof’s genetic study indicates that relatives of insects” “It’s like diving through Vaseline,” he says, a billion for each person on the planet. They once thought to be myriapods – land animals relatedness (Science, vol 346, p 763). This insect evolution really took off around describing the strange sensation of crossing have colonised every continent, including including millipedes and centipedes – but von confirmed their watery origins. “Insects are 440 million years ago, with an explosion of from the fresh surface water to the saltwater Antarctica. They can live in air, land and water. Reumont, an evolutionary biologist from the terrestrial crustaceans,” says Misof. And they species emerging. Then came a development below. Some 25 metres down, he enters a They even live on us – lice evolved as soon as University of Leipzig in Germany, and others evolved about 480 million years ago, the study that would take them to another level. narrow cavern filled with stalactites and there was hair and feathers to set up home in. had different ideas. In 2010, he published suggests, making them among the first things The oldest insect fossil ever found comes sculpted rocks, and it’s here, in this dark and They are the kings of the arthropods – animals research suggesting that the closest living ever to walk on land. Around this time, the from the rolling hills around the village of alien world, that he spots his quarry. The with hard exoskeletons – and the most relatives of insects are the aquatic remipedes. first terrestrial plants also evolved, which Rhynie in Aberdeenshire, UK. Those rocks are animal swimming into view in the light of his successful group of animals that has ever Similarities in their brains, nervous systems might have helped insects make the leap. teeming with tiny centipedes, mites, spiders lamp, searching for prey to impale with its lived. It’s something we have long known, yet and many of their proteins all point to an Whatever the spur, life on land came with and stubby plants, all petrified in the silica- venomous fangs, is a remipede. Although rare, we are only now starting to understand how ancient common ancestor, he says. That would formidable challenges, including dealing with rich waters of a volcanic hot spring around it is not just another curio. Remipedes are the they have come to dominate. mean not just that insects evolved in the dehydration, the effects of gravity, breathing 410 million years ago. But in 2004, Michael closest living relatives of the most successful Remipedes provide the first clue. watery margins between sea and land, but also air and daily extremes of temperature and Engel of the University of Kansas in Lawrence creatures on Earth – the insects. Crustaceans are among the earliest arthropods, that they are much older than we thought. CREATIVE GEOGRAPHIC ARK/NATIONAL GEOGRAPHIC PHOTO NATIONAL SARTORE, OEL solar radiation. A tough exoskeleton would found something else. Examining one of the > THE TRUSTEES OF THE NATURAL HISTORY MUSEUM, LONDON 34 | NewScientist | 7 November 2015 7 November 2015 | NewScientist | 35 Rulers of the Earth Ancient origins, ingenious innovations and admirable adaptability mean that insects comprise three-quarters of all known living animals 480 MYA ~420 MYA 310 MYA 323-252 MYA 252 - 201 MYA 145 - 65.5 MYA First insects First ying insects Complete metamorphosis Giant insects Beetlemania Age of butteries, bees and ants 320 MYA 252 MYA 66 MYA Folded wings Mass extinction Insects avoid mass extinction ORDOVICIAN SILURIAN DEVONIAN CARBONIFEROUS PERMIAN TRIASSIC JURASSIC CRETACEOUS PALAEOGENE NEOGENE Million 450 400 350 300 250 200 150 100 50 0 years ago First Vascular Trees Seed plants Flowering Grasslands terrestrial plants plants ecosystems THERE BE GIANTS fossils under the microscope he was The rhino beetle – just one spectacular example each followed by a moult, allowing miniature BANE OR BOON? transitional phase between larva and adult – gobsmacked to see tiny, perfectly preserved of more than 400,000 types of beetle forms resembling the adult to get evolved a way to store very high levels of Welcome to the Alice in Wonderland world mouthparts of a type only found in insects, progressively bigger. Complete There are many reasons to glycerol, helping it withstand freezing and starting in the Carboniferous some and not just any kind of insect. “This was our outwards from their bodies, even at rest, metamorphosis, by contrast, enabled the dislike insects. They spread desiccation, so making it very hardy during 320 million years ago, where familiar- first peek at a flying insect,” he says. Although making them vulnerable to damage and insects to divide their life cycle into distinct some of the world’s deadliest times of environmental stress. looking insects reached scarily unfamiliar its wings were not preserved, all the evidence limiting the habitats they could colonise. stages, with the larva specialised for feeding diseases including malaria and A recognisably more modern insect fauna sizes. The dragonfly-like Meganeuropsis, indicated that Rhyniognatha hirsti was a These “old-winged” insects were about be and the adult dedicated to reproducing. The typhoid. Some destroy crops. ushered in the Triassic. This period, 252 to or griffinfly, for example, had a wingspan relatively advanced flyer. This would make the upstaged, however. Down in the litter on the larva, pupa and adult stages of completely Others bore into wood. Stinging 201 million years ago, was boom time for of up to 70 centimetres. Arthropleura was origins of flight even earlier, perhaps at the forest floor were “new winged” insects with metamorphosing insects are thought to be the insects and parasites can make beetles. Not only were they small, fecund and a kind of millipede, but longer than a species explosion 440 million years ago. The hinge mechanisms to fold their wings over evolved equivalent of the pronymph, nymph life a misery. But just one insectCOPY SUB able to metamorphose, their forewings had human. How could they grow so big? oldest fossilised insect wing is 324 million years their bodies when not in use. This innovation and adult in ancestral insects. This in a thousand is a pest – most are hardened to protect their folded hindwings One answer is oxygen. Plants had old, so in one fell swoop, flight’s evolution has meant they could use hiding places and development has proved so successful that harmless and many beneficial.PAGE SUB and conserve moisture and warmth. They recently evolved the woody compound been pushed back more than 80 million years. habitats not available to their forebears. more than eight in 10 insect species use it Insects pollinate four-fifths of were able to colonise a huge range of habitats, lignin and, with no decomposing Misof’s study supports the date. Foremost among them were the ancestral today. Back then, though, Nel’s tiny insect the world’s crops, amountingOK to for press from deserts to ponds, and from the Arctic to organisms yet present to break it down, roaches, as successful then as they are today. fossils, which later evolved into beetles, fleas, G_Insectsone-third of food production, not the tropics. So successful were they that today trees were being buried rather than Yet the insects were to undergo a further wasps, bees and ants, were rarities. “Maybe the to mention our garden plants. there are at least 400,000 known beetle recycled. As a result, oxygen levels in the Up, up and away transformation – arguably the most important ecological niches were occupied by other We eat their honey, wear their species, more than any other type of insect. air reached 31 per cent, half as much again What got insects into the air? Engel suspects innovation of all, and its evolution was only groups and only after they became vacant silk and use their dyes and For insects, everything was coming up roses.