In Australia, a pair of superb fairy-wrens return to their nest with food for their newborn chick. As they arrive, the chick makes its begging call. It’s hard to see in the darkness of the domed nest, but the parents know that something isn’t right. Whatever’s in their nest, it’s not their chick. It doesn’t’ know the secret password. They abandon it, flying off to start a new nest and a new family somewhere else.
It was a good call. The bird in their nest was a Horsfield’s bronze-cuckoo. These birds are “brood parasites” – they lay their eggs in those of other birds, passing on their parenting duties to some unwitting surrogates. The bronze-cuckoo egg looks very much like a fairy-wren egg, although it tends to hatch earlier. The cuckoo chick then ejects its foster siblings from the nest, so it can monopolise its foster parents’ attention.
But fairy-wrens have a way of telling their chicks apart from cuckoos. Diane Colombelli-Negrel from Flinders University in Australia has shown that mothers sing a special tune to their eggs before they’ve hatched. This “incubation call” contains a special note that acts like a familial password. The embryonic chicks learn it, and when they hatch, they incorporate it into their begging calls. Horsfield’s bronze-cuckoos lay their eggs too late in the breeding cycle for their chicks to pick up the same notes. They can’t learn the password in time, and their identities can be rumbled.
Listen to this recording. It sounds like a drunkard playing a kazoo, but it’s actually the call of a beluga (a white whale) called NOC. Belugas don’t normally sound like that; instead, NOC’s handlers think that his bizarre sounds were an attempt at mimicking the sounds of human speech.
The idea isn’t far-fetched. Belugas are so vocal that they’re often called “sea canaries”. William Schevill and Barbara Lawrence – the first scientists to study beluga sounds in the wild – wrote that the calls would occasionally “suggest a crowd of children shouting in the distance”. Ever since, there have been many anecdotes that these animals could mimic human voices, including claims that Lagosi, a male beluga at Vancouver Aquarium, could speak his own name. But until now, no one had done the key experiment. No one had recorded a beluga doing its alleged human impression, and analysed the call’s acoustic features.
The male Japanese rhino beetle wields a huge forked horn on his head. It looks like a jousting weapon, and the male uses it to pry and flip other males off a branch. But it’s also a billboard, a prominent and completely honest advertisement for the male’s quality.
The horns are extremely variable. Small males have pathetic nubbins on their heads, while big ones have unfeasibly large prongs that can grow to two-thirds of their body length. Doug Emlen from the University of Montana has found that the growth of the horns is intimately tied into molecules that reflect how well-nourished the beetles are. Not only that, but the horn is more sensitive to these molecules than any other body part. Well-fed beetles may have larger wings and bodies than poorly-fed ones, but they have much larger horns.
This ornament can’t be faked. It is impossible for a weak beetle to feign rude health by growing a larger horn, so females can rely on the size of the horns to judge a potential partner’s health. And with a body part that conspicuous, they don’t have to look very hard.
The growth of the horns depends on insulin and related molecules called insulin-like growth factors (IGFs). Most people know insulin as the substance that some diabetics have to take, but it and the IGFs are also major players in animal development. Their levels change depending on nutrition, stress and infections, and they control how fast different tissues can grow. They fine-tune the size of an animals’ body so that it’s appropriately sized for the environmental challenges it will face. If there’s plenty of food around, a bigger body will do well, and insulin and IGFs ensure that one is produced.
If every body part was equally responsive to insulin and IGFs, then every bit of an animal would grow at the same size. A big individual would just be a scaled-up version of a small one. But this doesn’t always happen. Some body parts ignore the signals and are much the same size in every individual – the genitals of many insects are a good example. Others, like the rhino beetle’s borns, are hypersensitive and grow huge, out of all proportion to the rest of their bearer’s anatomy.
Emlen studied the beetles’ horns by interfering with their insulin receptors, the molecules that insulin docks with. Without these receptors, insulin becomes a messages without a listener – it has no influence. Emlen silenced the receptors when the beetles were finishing up their larval careers, and ready to transform into adults. At this point, their body size is roughly set, but their adult body parts, like horns, wings and genitals, were still getting bigger.
The loss of insulin signals didn’t affect the beetles’ genitals – they were the same size as those of normal insects. It did, however, make their wings around 2 percent smaller. And it made their horns a whopping 16 percent smaller. This means that the horns are 8 times more sensitive to insulin than wings (which are representative of most other body parts).
Insulin and IGF help to set the size of many other exaggerated animal ornaments, including the antlers of red and fallow deer, the horns of dung beetles, and the giant claws of some crustaceans. You can understand why. These hormones have been coupling the growth of animals to environmental conditions for half a billion years. They form a widespread system, and an easy one to tweak. If a body part becomes subtly more sensitive to these signals, then – Bam! – it’s free to outpace the rest of the body in size.
Here’s the important thing: a change like that would necessarily produce body parts that honestly indicate their owner’s quality. Weak, starving individuals can’t produce big ornaments, because the size of those ornaments is tied to their insulin levels and their insulin levels are tied to their nutritional state. They can’t fake their way to showiness.
This is a subtly different explanation to the one that’s often put forward to explain the evolution of flashy animal ornaments – the handicap principle. It states that low-quality individuals can’t bear the cost of, say, a long tail or a magnificent set of antlers. They would be too conspicuous or heavy. They need strength and health to pull off. Cheats couldn’t bear the burden.
You can understand how the handicap principle would work for a signal that’s already exaggerated, but obviously, those signals didn’t start off that way. They would have had much humbler and smaller origins, when the costs of bearing them would have been low. So, at this early stage of evolution, why didn’t weak individuals cheat by producing larger ornaments?
Emlen’s rhino beetles provide an answer. The signals can’t be faked not because they’re a drain, but because they’re intimately tied into an individual’s physical condition. It’s not that cheaters can’t carry the burden of big ornaments. It’s that cheaters can’t exist.
Reference: Emlen, Warren, Johns, Dworkin & Lavine. 2012. A Mechanism of Extreme Growth and Reliable Signaling in Sexually Selected Ornaments and Weapons. Science http://dx.doi.org/10.1126/science.1224286
More on extreme body parts:
As first light tickles the air, songbirds croon to proclaim their territories and woo potential mates. There are many possible explanations for the timing of the beautiful dawn chorus, including the fact that sound travels further during the early hours of the day.
But Michael Beaulieu and Keith Sockman from the University of North Carolina have found another for the list. It’s based on a very simple observation: dawn is often very cold. And female Lincoln’s sparrows find songs sexier if they hear them in the cold.
Anglers ensnare fish with bait, or with man-made lures that look like bait. Anglerfish do the same thing – they have worm-like growths on their heads that act as living fishing lures to entice their prey. The swordtail characin, a small fish from Trinidad and Venezuela, has a similar lure, and it uses it not to attract food, but sex.
The male characin has a small bean-shaped patch attached to his gill flaps by a thin thread. When he swims, he holds these ‘flags’ against his body. When he encounters a female, he flares one of them out in front of her. The female clearly thinks that the flag is food, for she bites at it vigorously. While she’s occupied, the male sidles across and impregnates her with his sperm.
Unlike many other fish, which shoot sperm and eggs into the water, characins fertilise each other internally, just like us. The male, however, doesn’t have any sort of penetrating organ, so he needs to bump into the female just so. And his bizarre ornament ensures that she’s in exactly the right place.
Niclas Kolm and Göran Arnqvist have been studying the characins for several years, and they’ve shown that characins from different Trinidadian streams have distinctly shaped flags. Now, they think they know why.
The characins feed on manna from heaven – insects that fall into the water from overhanging plants. On average, half of their diet consists of tree-dwelling ants, but that proportion can vary between 10 and 75 per cent. The ant portion of their menu is dictated by their environment: if they live in wider streams, they have more plants growing overhead, and more ants fall within their reach. Now, Kolm and Arnqvist have shown that the flags of male characins look more like ants in streams where the female eats more ants.
Together with Mirjam Amcoff and Richard Mann, they captured characins from 17 different streams around Trinidad. They measured the shape of the male’s flag and the contents of the female’s guts, and showed that these traits are related. In streams where females eat more ants, the males’ flags are more tapered and curved towards their far end. This more closely mimics the shape of an ant with its narrow waist connecting a thick torso and abdomen. It’s very different to the oval shape of a beetle – the characins’ second favourite food.
Are these ant-like flags more successful at attracting ant-eating females? Kolm and Arnqvist found out by using characins that had been raised in captivity, and had never seen an ant before. They fed these females with either ants or other insects, before presenting them with males from different streams. Sure enough, females that had gorged on ants were more likely to attack the ant-like flags of males from streams where females naturally eat lots of ants.
It’s a really elegant experiment – one that strongly supports the idea that the male flags have evolved to tap into the sensory biases of the females. As Kolm writes, “The shape of the male flag ornament…has evolved to track the search images that females employ in foraging.” It’s a lure that evolves according to the preferences of its target.
But the important thing here is that those preferences are originally driven by the environment. It’s the width of the streams that determines how many ants the females encounter, and thus what shapes the males’ lures take. This process, where animal signals evolve to account for the properties of their environment and stand out more strongly, is known as sensory drive. And in this case, it’s driving the divergence of different characin populations.
Reference: Kolm, Amcoff, Mann & Arnqvist. 2012. Diversification of a Food-Mimicking Male Ornament via Sensory Drive. Current Biology http://dx.doi.org/10.1016/j.cub.2012.05.050
Here’s the fourth piece from my new BBC column
“What’s that Flipper? The treasure is over there?” So went a typical plotline for the popular TV series featuring the cute, bottlenosed dolphin who could communicate with his human guardians, and who – in the time-honoured fashion – used his animal powers to apprehend criminals.
The idea that animals like Flipper can communicate with humans is not just the preserve of the small and big screen. History is littered with celebrity animals who have communicated with human scientists, with varying degrees of success. Many apes, including Washoe and Nim the chimps, and Kanzi the bonobo, have learned to communicate by using sign language or symbols on a keyboard. Alex, an African grey parrot learned over 100 English words, which he could use and combine appropriately; his poignant last words to Irene Pepperberg, his scientist handler, were “You be good. I love you. See you tomorrow.”
Dolphins hold a particular fascination; we are captivated by their intelligence and beauty, and swimming with dolphins features regularly on lists of things to do before you die. Denise Herzing has a lifetime of such experiences. For the last 27 years, she has been swimming with a group of Atlantic spotted dolphins in Florida as part of the Wild Dolphin Project. She can identify every individual and they, in turn, seem to trust and recognise her. It is a solid foundation for the boldest attempt yet to talk with dolphins.
“Talk” is tricky to define. A SeaWorld trainer who prompts a dolphin to jump for fish is arguably communicating with it. But such simple one-way interactions are a far cry from the conversational world of Dr Doolittle. Here, the dolphin responds, but says nothing intelligible back. Herzing’s vision is much more ambitious – she wants to establish two-way communication with her dolphins, with both species exchanging and understanding information.
The idea of talking to dolphins has a long and chequered history. It was widely publicised in the 1960s by John Lilly, who argued that dolphins have such large brains that they must be extremely intelligent and have a natural language. All we had to do was to “crack the code”. Much of Lilly’s work was highly questionable. He once flooded a house to keep a captive dolphin, instigated failed attempts to teach them spoken English, and even gave the animals LSD (while taking the drug himself). But there is no denying his influence in popularising the idea of two-way dolphin communication. “He said that in a few years, we will have established complex dialogue with them,” says Justin Gregg from the Dolphin Communication Project. “And he was saying that every few years.”
Lilly was right about dolphin intelligence, but not dolphin language. A true language involves small elements that combine into larger chains, to convey complex, and sometimes abstract, information. And there is no good evidence that dolphins have that, despite their rich repertoire of whistles and clicks.
Little less conversation
Wild dolphin communication is hard to study. They are fast-moving and hard to follow. They travel in groups, making it hard to assign any call to a specific individual. And they communicate at frequencies beyond what humans can hear. Despite these challenges, there is some evidence that dolphins use sounds to represent concepts. Each individual has its own “signature whistle” which might act like a name. Developed in the first year of life, dolphins use these whistles as badges of identity, and may modulate them to reflect motivation and mood. This year, a study showed that when wild dolphins meet, one member of each group exchanges signature whistles.
But beyond this, dolphin chat is still largely mysterious. “To communicate with dolphins, we need to understand how they communicate with each other in the natural world,” says psychologist Stan Kuczaj at the University of Southern Mississippi. “We still don’t know basic things like what the units of dolphin communication are. Is a whistle the equivalent of a “word” or a “short sentence”? We don’t know.”
We may not be able to understand them yet, but we know that dolphins can learn to understand us. In the 1970s, Louis Herman taught an invented sign language, complete with basic syntax, to a bottlenose dolphin called Akeakamai. For example, if he made the gestures for “person surfboard fetch”, Akeakamai would bring the board to him, while “surfboard person fetch” would prompt her to carry the person to the board. His experiments showed that dolphins could understand hundreds of words, and how those words could be combined using grammatical rules.
What’s my motivation?
Herman’s work was groundbreaking, but this was still one-way communication. It focused on comprehension, not conversation. In the 1980s, Diana Reiss had more luck by showing that dolphins could use underwater keyboards to make basic requests. When they prodded keys with their snouts, a whistle would play and Reiss gave a reward like a ball. Eventually, the dolphins used the artificial whistles to ask for the associated rewards.
But as conversations go, these were shallow ones. “The dolphins were only really interested in communicating about needs that they had, like a tool they needed or a fish they wanted,” says Kuczaj, who was involved in a similar project at DisneyWorld’s EPCOT Center. “We hoped they would also comment on other things going on in the aquarium but they didn’t.”
It is difficult persuading dolphins to learn some arbitrary signals, like a whistle signifying a ball, and then use them in a social context, admits Gregg. “They don’t seem to run with it the same way that chimps or bonobos have. The big stumbling block is motivation. Dolphins don’t seem to care.”
Herzing disagrees. She notes that captive animals, which often lack stimulation, will respond to systems like the underwater keyboards. She thinks that these experiments disappointed because they were cumbersome. “The dolphins swim very fast and went to where they were requested, but humans are very slow in the water. There wasn’t enough real-time interaction.”
Herzing is trying to solve that problem with Cetacean Hearing and Telemetry (CHAT) – a lighter, portable version of the underwater keyboards. It consists of a small phone-sized computer, strapped to a diver’s chest and connected to two underwater recorders, or hydrophones. The computer will detect and differentiate dolphin sounds, including the ultrasonic ones we cannot hear, and use flashing lights to tell the diver which animal made the call.
The CHAT device can also play artificial calls, allowing Herzing to coin dolphin-esque “words” for things that are relevant to them, like “seaweed” or “wave-surfing”. She hopes the dolphins will mimic the artificial whistles, and use them voluntarily. By working with wild animals, and focusing on objects in their natural environment, rather than balls or hoops, Herzing hopes to pique their interest.
Herzing emphasises that her device is not a translator. It will not act as a dolphin-human Rosetta stone. Instead, she wants both species create a joint form of communication that they are both invested in. She hopes that CHAT will tap into the “natural propensity” that dolphins have “for creating common information when they have to interact”. For example, in Costa Rica, distantly related bottlenose and Guyana dolphins will adopt a shared collection of sounds when they come together, using sounds that they don’t use when apart.
As with past projects, all of this depends on whether the dolphins play along. Kuczaj says, “It’s a remarkable challenge because she is working with wild dolphins so they’ve got the option to participate or not.” Here, Herzing has an edge, since the animals know her, and vice versa. “We’ve been observing them underwater every summer since 1985,” she says. “I know the individuals personally – their personalities and relationships. We’ve got a pretty good handle on what they’d be interested in.” Perhaps this combination of cutting-edge technology and old-school fieldwork will finally produce the conversations that have eluded scientists for so long.
When we meet a group of strangers, one of the first things we’ll do is to introduce ourselves by name. Nicola Quick and Vincent Janik from the University of St Andrews have found that groups of bottlenose dolphins do something similar. When they meet one another in the wild, they exchange “signature whistles”. These whistles are unique to each individual, and they’re strikingly similar to human names. And it seems that they’re a standard part of a dolphin’s meet-and-greet etiquette.
When we make decisions, our brains are abuzz with agreements and vetoes. Groups of neurons represent different choices, and interact with one another until one rises to the fore. The neurons excite some of their neighbours into firing in tandem, while suppressing others into silence. From this noisy cross-talk, a choice emerges.
The same thing happens in a bee hive. The entire colony, consisting of tens thousands of individuals, works like a single human nervous system, with each bee behaving like a neuron. When they make a decision, such as choosing where to build a nest, individual bees opt for different choices and they support and veto each other until they reach a consensus. They have, quite literally, a hive mind.
The melody sounds like it comes from a single bird, but it is actually sung by two: one male and one female. The couple alternates their syllables with almost unbelievable precision, each one placing its notes in the gaps left by its partner. The result is one of nature’s finest duets. And the singers are a pair of (rather drably named) plain-tailed wrens.
By studying the singing wrens, Eric Fortune from Johns Hopkins University has found that each bird has brain circuits that encode the entire song. Rather than focusing on just their own contribution, they process the whole melody. Their duet is conceived as a whole in both their brains, but emerges as two distinct parts, one from each beak.
If you go down to the woods of California today, you might be in for a big surprise. At night, the forests crawl with sinuous shapes that glow with an eerie greenish-blue colour. They are Motyxia millipedes and they shine brightly whenever they’re disturbed. “If you go to the right forest and you let your eyes get adjusted to the night, then you can see them everywhere,” says Paul Marek from the University of Arizona. Some big oak tress can shelter 1 glowing millipede in every square metre. They look like fields of stars.
There are around 12,000 known species of millipedes, and only the eight Motyxia species glow. Marek says, “[They] would definitely be on my top 10 for my imaginary “millipede biodiversity global tour” (along with the shocking pink millipede in Thailand & the longest millipede in Africa).”
But why do the Californian ones glow? Marek knows the answer. With hundreds of millipedes, some clay, and a bit of paint, he has shown that they light up to ward off predators. You might expect that the light shows would make the millipedes easier to find and eat. In fact, it deters hungry mouths.