Some folks just can’t help being loud in bed, but noisy liaisons can lead to a swift death… at least for a housefly. In a German cowshed, Natterer’s bats eavesdrop on mating flies, homing in on their distinctive sexual buzzes.
Based on some old papers, Stefan Greif form the Max Planck Institute for Ornithology knew that Natterer’s bats shelter in cowsheds and sometimes feed on the flies within. What he didn’t know was how the bats catch insects that they shouldn’t be able to find. They hunt with sonar, releasing high-pitched squeaks and visualising the world in the returning echoes. Normally, the echoes rebounding from the flies would be masked by those bouncing off the rough, textured surface of the shed’s ceiling. The flies should be invisible.
And they mostly are. Greif filmed thousands of flies walking on the shed’s ceiling, and not a single one of them was ever targeted by a bat. That changed as soon as they started having sex. Greif found that a quarter of mating flies are attacked by bats. Just over half of the attacks were successful and in almost all of these, the bat swallowed both partners.
Mythology imbues the vampire bat with supernatural powers, but its real abilities are no less extraordinary. Aside from its surprising gallop and its anti-clotting saliva, the bat also has a heat-seeking face. From 20 centimetres away, it can sense the infrared radiation given off by its warm-blooded prey. It uses this ability to find hotspots where blood flows closest to the skin, and can be easily liberated by a bite. Now, Elena Gracheva and Julio Cordero-Morales from the University of California, San Francisco have discovered the gene behind this ability.
Among the back-boned vertebrates, there are only four groups that can sense infrared radiation. Vampire bats are one, and the other three are all snakes – boas, pythons, and pit vipers like rattlesnakes. Last year, Gracheva and Cordero-Morales showed that the serpents’ sixth-sense depends on a gene called TRPA1, the same one that tells us about the pungent smells of mustard or wasabi. Boas, pythons and vipers have independently repurposed this irritant detector into a thermometer.
Vampire bats evolved their ability in a similar way, but they have tweaked a different protein called TRPV1 that was already sensitive to heat. Like TRPA1, TRPV1 also alerts animals to harmful substances. It reacts to capsaicin, the chemical that makes chillies hot and allyl isothiocyanate, the pungent compound that gives mustard and wasabi their kick. In humans, it also responds to any temperature over 43 degrees Celsius. The vampire has simply tuned it to respond to lower temperatures, such as those of mammal blood.
Pollination is the process whereby plants turn animals into sex toys. With nutritious nectar, striking flowers (and the odd bit of deceit), they lure in animal carriers that can transport their pollen to another flower. These partnerships have painted the world in a resplendent palette of flowery hues. But pollination can create other feasts for the senses that are oblivious to us visually focused humans.
The Cuban rainforest vine Marcgravia evenia is pollinated by bats, which find their way around with sonar rather than sight. They make high-pitched clicks and time the returning echoes to “see” the world in rebounding sound. And M.evenia exploits that super-sense with a leaf that doubles as a sonar dish. It reflects the bats’ calls into strong, distinctive echoes, creating a sonic beacon that stands out among the general clatter of the forest.
The wings of bats provide them with support and lift as they fly. But they are also giant sensors that tell bats about the flow of air around their bodies, helping them to execute sharp manoeuvres without crashing.
The wings’ ability to monitor airflow depends on tiny hairs that cover their surfaces. The hairs were discovered almost a century ago. Scientists suggested that they are sense organs that allow bats to fly in complete darkness. That idea fell out of favour in the 1940s when Donald Griffin and Robert Galambos showed that bats navigate by listening for the echoes of their own calls. The discovery of bat sonar solved the mystery of their night-time aerobatics, and the wing hairs fell into obscurity.
But John Zook at Ohio University had not forgotten about them. He has shown that the pre-sonar theories were partly correct. The hairs complement a bat’s echolocation and turn it into a better flier, allowing the animal to “feel” its way through the sky.
Every year, in mid-September, big brown bats throughout Colorado head for their favourite roosts, where they will spent the winter in hibernation. But some of the bats won’t sleep alone – they are carrying the rabies virus, and it will also hibernate through the winter in its slumbering host.
The rabies virus is a killer. Infections are almost always fatal, and around 55,000 people around the world succumb to the virus every year. Dogs are the leading carriers, but in North America, vaccination programmes have effectively eliminated dog rabies. Bats are another story – they are far more difficult to vaccinate and they have overtaken man’s best friend as the leading cause of American rabies.
Now, Dylan B. George from Colorado State University has shown that the rabies virus, by hibernating alongside the big brown bats, gets a free pass to the next generation.
The world’s worst flesh-eating plant lives in the jungles of Borneo. It’s called elongata and it’s one of several strains of Raffles’ pitcher plant. Like its relatives, it has distinctive pitcher-shaped leaves that can lure insects into a watery grave. But unlike other strains, elongata is strangely incompetent at catching insects. Instead, it lures bats into its pitchers, and lives off their poo.
A bat, flying through the night sky, is thirsty. As it flies, it sends out high-pitched squeaks and listens for the returning echoes. It hears a telltale pattern. It hears no echoes form up ahead and the only ones that reflect back at it are coming from straight below. That only happens when the bat flies over a flat, smooth surface like the top of a lake or pond. The bat dives, opens its mouth to take a sip of refreshing water… and gets a mouthful of metal.
In nature, bodies of water are the only large, smooth surfaces around. Waves of sound that hit the surface of still water would generally bounce away, except for those aimed straight downwards. Stefan Greif and Björn Siemers from the Max Planck Institute for Ornithology have found that bats are instinctively tuned to find water using this unique feature (and yes, the institute does mostly, but not exclusively, bird research).
The night sky is the setting for an arms race that has been going on for millions of years: a conflict between bats and moths. Many bats can find their prey by giving off high-pitched squeaks and listening out for the echoes that return. This ability – echolocation – allows them to hunt night-flying insects like moths, which they skilfully pluck out of the air. But moths have developed countermeasures; some have evolved ears that allow them to hear the calls of a hunting bat and take evasive action. And bats, in turn, have adapted to overcome this defence.
Holger Goerlitz from the University of Bristol has found that the barbastelle bat is a stealth killer that specialises in eating moths with ears. Its echolocation calls are 10 to 100 times quieter than those of other moth-hunting bats and these whispers allow it to sneak up on its prey. It’s the latest move in an ongoing evolutionary dogfight and for now, the barbastelle has the upper wing.
Not Exactly Pocket Science is a set of shorter write-ups on new stories with links to more detailed takes. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Spongebob’s genome reveals the secrets of building an animal
Sponges are animals but, outside of children’s cartoons, they’re about as different from humans as you can imagine. These immobile creatures lie on the very earliest branch on the animal family tree. They have no tissues or organs – their bodies are made of just two layers of cells, twisted and folded into simple shapes. But despite this simplicity, the first complete sponge genome tells us a lot about what it takes to build an animal.
The genome was sequenced from an Australian species called Amphimedon queenslandica by a large team of scientists led by Mansi Strivastava from the University of California, Berkeley. It tells us that sponges share a ‘genetic toolkit’ with humans and all other animals. This includes 4,670 families of genes that are universal to all animals, 1,286 of which separate us from our closest single-celled relatives, the choanoflagellates. Within these families lie the keys to a multicellular existence.
This shared toolkit controls all the fundamental processes that allow individual cells to cooperate as part of a single creature, including how to divide, die, grow together, stick to one another, send signals to one another, take up different functions, and tell the difference between each other and outsiders. They also include many genes that are implicated in cancer, a disease where individual cells go rogue and multiply out of control at the expense of the collective. The presence of cancer-related genes in the sponge genome tells us that as long as cells have been cooperating within a single body, they have needed to guard against the threat of cancer.
Srivastava estimates that the foundations of multicellular life were laid between 600 and 800 million years ago. More than a quarter of the big genetic changes that separate humans from the single-celled choanoflagellates took place during this window, before sponges split off from the ancestors of all other animals. The last common ancestor of all animals emerged during this period and it was a creature of remarkable complexity – a multicellular species that could sense, react to and exploit its environment.
Holy extinction, Batman! One of America’s most common bats could be wiped out in 16 years by new disease
The little brown bat is one of the most common bats in North America but in 16 years, people on the East Coast will be lucky to see any. The bat is being massacred and the culprit is a new disease known as white-nose syndrome caused by the ominously named fungus Geomyces destructans. The fungus grows on the wings, ears and muzzles of hibernating bats, rousing them too early from their deep sleep, sapping their fat reserves and causing strange behaviour.
White-nose syndrome was first identified in a New York cave in February 2006, but it spreads fast. In the last four years, it has covered over 1200 km and contaminated wintering roosts throughout the north-eastern US and its neighbouring Canadian provinces. In infected areas, the fungus is slaughtering bats at a rate of around 45% a year. Cave floors are littered with carcasses.
Five years ago, the little brown bat was thriving, thanks to the installation of bat boxes, conservation efforts and a reduction in pesticide use. The eastern seaboard alone was home to 6.5 million of them. But all of that good is being undone by a single disease. Using a mathematical model, Winifred Frick from Boston University calculated a 99% chance that the species will become locally extinct within 16 years. Even if the current death rate slows to just 5% a year – a highly optimistic target– the population will still collapse to around 65,000 individuals. These last survivors would be just 1% of the previous total, with a 60% chance of dying off by the end of the century. At this stage, the question isn’t if the little brown bat will go locally extinct, but when.
This is just the tip of the iceberg. White-nose syndrome is spreading across North American and at least six other bat species are affected. These animals eat such a large volume of insects that their disappearance would have severe economic and ecological consequences. There’s a desperate need for more research to understand the disease, to keep a track of it, to find ways of fighting it, and to ensure that something like it doesn’t happen again. Frick thinks that white-nose syndrome spread so quickly with such devastating results that it must have been introduced from another part of the world, hitting species whose immune systems were totally unprepared for it. This problem of “pathogen pollution” is a neglected issue in conservation – perhaps the demise of the little brown bat will provide the impetus to take it seriously.
Reference: Science http://dx.doi.org/10.1126/science.1188594
Most mammals can trace their origins to a single ancestral species. But in the Caribbean islands of the Lesser Antilles, there is a fruit bat with a far more complex family tree. Artibeus schwartzi’s genome is a hybrid mish-mash of DNA inherited from no less than three separate ancestors. One of these is probably extinct and the other two of which still live on the same island chain. It’s a fusion bat, a sort of fuzzy, winged spork.