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 by the world’s best journalists and bloggers. It is meant to complement the usual fare of detailed pieces that are typical for this blog.
Geneticist sequences own genome, finds genetic cause of his disease
If you’ve got an inherited disease and you want to find the genetic faults responsible, it certainly helps if you’re a prominent geneticist. James Lupski (right) from the Baylor College of Medicine suffers from an incurable condition called Charcot-Marie-Tooth (CMT) disease, which affects nerve cells and leads to muscle loss and weakness.
Lupski scoured his entire genome for the foundations of his disease. He found 3.4 million placed where his genome differed from the reference sequence by a single DNA letter (SNPs) and around 9,000 of these could actually affect the structure of a protein. Lupski narrowed down this list of candidates to two SNPs that both affect the SH3TC2 gene, which has been previously linked to CMT. One of the mutations came from his father and the other from his mother. Their unison in a single genome was the cause of not just Lipson’s disease but that of four of his siblings too.
It’s a great example of how powerful new sequencing technologies can pinpoint genetic variations that underlie diseases, which might otherwise have gone unnoticed. The entire project cost $50,000 – not exactly cheap, but far more so than the sequencing efforts of old. The time when such approaches will be affordable and commonplace is coming soon. But in this case, Lupski’s job was easier because SH3TC2 had already been linked to CMT. A second paper tells a more difficult story.
Jared Roach and David Gallas sequenced the genomes of two children who have two inherited disorders – Miller syndrome and primary ciliary dyskinesia – and their two unaffected parents. We don’t know the genetic causes of Miller syndrome and while the four family genomes narrow down the search to four possible culprits, they don’t close the case.
For great takes on these stories and their wider significance, I strongly recommend you to read Daniel Macarthur’s post on Genetic Future, Mark Henderson’s piece in the Times and Nick Wade’s take in the NYT (even if he does flub a well-known concept). Meanwhile, Ivan Oranksy has an interesting insight into the political manoeuvres that go into publicising two papers from separate journals. And check out this previous story I wrote about how genome sequencing was used to reverse the wrong diagnosis of a genetic disorder.
Male moths freeze females by mimicking bats
Flying through the night sky, a moth hears the sound of danger – the ultrasonic squeak of a hunting bat. She freezes to make herself harder to spot, as she always does when she hears these telltale calls. But the source of the squeak is not a bat at all – it’s a male moth. He is a trickster. By mimicking the sound of a bat, he fooled the female into keeping still, making her easier to mate with.
The evolutionary arms race between bats and moths has raged for millennia. Many moths have evolved to listen out for the sounds of hunting bats and some jam those calls with their own ultrasonic clicks, produced by organs called tymbals. In the armyworm moth, only the males have these organs and they never click when bats are near. Their tymbals are used for deceptive seductions, rather than defence.
Ryo Nakano found that the male’s clicks are identical to those of bats. When the males sung to females, Nakano found that virtually all of them mated successfully. If he muffled them by removing the tymbals, they only got lucky 50% of the time. And if he helped out the muted males by playing either tymbal sounds or bat calls through speakers, their success shot back up to 100%. Nakano says that this is a great example of an animal evolving a signal to exploit the sensory biases of a receiver.
More on bats vs. moths from me
Reference: Biology Letters http://dx.doi.org/10.1098/rsbl.2010.0058
Millions of years before humans invented sonar, bats and toothed whales had mastered the biological version of the same trick – echolocation. By timing the echoes of their calls, one group effortlessly flies through the darkest of skies and the other swims through the murkiest of waters. It’s amazing enough that two such different groups of mammals should have evolved the same trick but that similarity isn’t just skin deep.
The echolocation abilities of bats and whales, though different in their details, rely on the same changes to the same gene – Prestin. These changes have produced such similar proteins that if you drew a family tree based on their amino acid sequences, bats and toothed whales would end up in the same tight-knit group, to the exclusion of other bats and whales that don’t use sonar.
This is one of the most dramatic examples yet of ‘convergent evolution’, where different groups of living things have independently evolved similar behaviours or body parts in response to similar evolutionary pressures.
It is one of a growing number of studies have shown that convergence on the surface – like having venom, being intelligent or lacking enamel – is borne of deeper genetic resemblance. But this discovery is special in a deliciously ironic way. It was made by two groups of scientists, who independently arrived at the same result. The first authors even have virtually identical names. These are people who take convergence seriously!
Many humans whinge about not getting oral sex often enough, but for most animals, it’s completely non-existent. In fact, we know of only animal apart from humans to regularly engage in fellatio – the short-nosed fruit bat (Cynopterus sphinx).
The bat’s sexual antics have only just been recorded by Min Tan of China’s Guangdong Entomological Institute (who are either branching out, or are confused about entomology). Tan captured 60 wild bats from a nearby park, housed them in pairs of the opposite sex and voyeuristically filmed their liaisons using a night-time camera. Twenty of the bats got busy, and their exploits were all caught on video.
Male bats create tents by biting leaves until they fall into shape. These provide shelter and double as harems, each housing several females who the male mates with. Fruit bat sex goes like this: the female approaches and sniffs the male, and both partners start to lick one another. The male makes approaches with his thumbs (like the Fonz) and mounts the female (like the Fonz). Sex itself is the typical rhythmic thrusting that we’re used to, and afterwards, the male licks his own penis for several seconds.
But Tan also found that female bat will often bend down to lick the shaft of her mate’s penis during sex itself. This behaviour happened on 70% of the videos, making it the only known example of regular fellatio in a non-human animal. It also prolonged the sexual encounter – males never withdrew their penises when they were being licked and, on average, the behaviour bought the couple an extra 100 seconds of sex over and above the usual 2 minutes. The licking itself only lasted for 20 seconds on average, so each second of it buys six extra seconds of penetration.
NSFW – short-nosed fruit bats having sex. I will have you know that the music choice came with the video and has nothing to do with me.
Oral sex is rare in other animals. Bonobos do it (but really, what don’t they do?) but it’s more of a form of play among young males, and there’s one anecdotal instance of an orang-utan doing the same. Some animals, such as ring-tailed lemurs, lick each other’s genitals to judge whether they’re ready for mating, but there’s no evidence that they do so as an actual part of sex. As for other bats, it’s entirely possible that they too engage in oral sex. However, given their inaccessible roosts and nocturnal habits, we’re largely in their dark about their sex lives.
Nonetheless, Tan suggests a few possible reasons for the short-nosed fruit bat’s penchant for fellatio, aside from the anthropocentric conclusion of ‘pleasure-giving’. Bat penises contain erectile tissue much like our own. It gets stiffer if it’s stimulated, so females could use oral sex to prolong their encounters with males, by maintain their erections or lubricating it for easier entry.
While many of us might nod sagely at the need for longer sex, Tan suggests that for the bats, it could mean easier transport of sperm to the oviduct, or more secretions from the female that are conducive to fertilisation. It could also be a way of hogging a mate, keeping him away from rival females.
Alternatively, the antiseptic properties of saliva might help to strip the male’s penis of bacteria or fungi, and prevent the spread of sexually transmitted diseases. The fact that males lick their own penises after sex supports this idea.
And finally, oral sex might help females to pick up chemical traces on her mate that might suggest if he’s a suitable mate. Obviously, they’d already be having sex, but female mammals often exert choice over their sexual partners after the fact, rejecting sperm from inferior males, or encouraging congress with superior ones to displace it. All of these explanations are just hypotheses for the moment, but they could all be tested in the future.
Reference: Tan, M., Jones, G., Zhu, G., Ye, J., Hong, T., Zhou, S., Zhang, S., & Zhang, L. (2009). Fellatio by Fruit Bats Prolongs Copulation Time PLoS ONE, 4 (10) DOI: 10.1371/journal.pone.0007595
More on animal sex:
When food is precious, animals can resort to strange behaviours in order to satisfy their hunger. Take the great tit. Its usual diet of insects and creepy-crawlies is harder to come by in winter. But in one Hungarian cave, great tits, ever the opportunists, have learned to exploit a rich and unusual source of food. They kill sleeping bats.
Great tits are only about 5 inches long, but their prey – the pipistrelle bat – is smaller still, just an inch or two in size. The bats spend the winter months hibernating in rock crevices. They’re well hidden, but when they wake up, they start making noises and these are the telltale signs that the birds are listening out for. They hunt by flying slowly and systematically across the cave walls, eavesdropping on the bats’ noises, and killing them while they’re still woozy.
Peter Estok from Germany’s Max-Planck Institute for Ornithology spent two winters watching a group of around 50 great tits hunting for bats. Previously, there had only been a smattering of anecdotal evidence that this happened. In one case, a tit was found eating a dead bat outside a Polish cave, but it could well have been scavenging off an already deceased corpse. Then, thirteen years ago, Estok saw a great tit capturing a live bat in a Hungarian cave. He was intrigued and he returned to the cave several times for more observations.
Tits lack the obvious killing apparatus of birds of prey but their short beaks are strong enough to dismember a tiny pipistrelle. Estok saw several instances of actual kills and recovered a few carcasses that showed obvious bite wounds. The bodies were picked clean enough to suggest that the birds were killing the bats for food and not, say, to remove competition for roosting spots.
When sportsmen use rackets or bats, their best bet is to hit a ball on the “sweet spot”, the point where various forces balance out to deliver powerful blows with only very small forces on the wielder’s wrist. Engineers have the right tools and models to work out where this spot lies on their instruments. Now, palaeontologists have used the same techniques to study biological hammers that adorn the tails of giant prehistoric armadillos called glyptodonts.
At first glance, glyptodonts have little in common with the likes of Andy Murray and Roger Federer. These armoured beasts lived in the Americas several million years ago and the largest of them weighed up to two tons. Much like their modern armadillo relatives, they were clad in large suits of bony armour. Their long tails were similarly protected by bony rings and in some species, they were topped with large clubs, or spiky weapons that resembled medieval morning stars.
Uruguayan scientist Rudemar Ernesto Blanco was set about studying the tail clubs of the most formidable of the glyptodonts, by using the same approaches used to analyse sports tools. The analogy is particularly appropriate for species like Doedicurus, where the rings at the end of the tail were completely fused, meaning that the animal’s rear end was defended by a single metre-long piece of solid bone – a biological hammer, indeed.
When wielding this weapon, whether against a predator or a fellow glyptodont, it would be in the animal’s interest to strike at the sweet spot of its own tail to reduce the forces acting on the part of the tail where the bony tip met the more flexible base. Otherwise, it might have risked severe strain and damage. To find the locations of these spots, Blanco applied sports modelling techniques to the tails of nine species of glyptodonts.
Bats view the world in echoes, timing the reflections of their own ultrasonic calls to navigate and hunt. This biological sonar, or echolocation, has made them masters of the night sky; it’s so sensitive that some species take moths and other insects on the wing, while others pluck spiders from their webs without entangling themselves in silk. But with such an efficient technology, it was only a matter of time before their quarry developed countermeasures.
Some insects gained ears; others simply rely on outmanoeuvring their attackers. But one group, the tiger moths, play bats at their own game. When attacked, they unleash ultrasonic clicks of their own to jam the calls of their pursuers, disrupting their ability to accurately gauge distances or even feigning echoes off non-existent objects.
This technique has been suggested ever since moths were first discovered to click several decades ago, but Aaron Corcoran from Wake Forest University has found the first conclusive evidence that moths actually do this. They pitted moths of the species Bertholdia trigon) against four big brown bats (Eptesicus fuscus) against each other over the course of three days, in gladiatorial arenas surveyed by high-speed infrared cameras and ultrasonic microphones.
When the three bats were pitted against moths in flight, they only managed to snag B.trigona on around one in five attempts. Even if the moths were tethered onto a stump, the bats still fumbled their approach at the last minute. A related moth species that doesn’t click fared much worse and almost always succumbed to the bats.