From Crickets to Whales, Animal Calls Have Something in Common

(Jan. 6, 2010) — Scientists who compare insect chirps with ape calls may look like they are mixing aphids and orangutans, but researchers have found common denominators in the calls of hundreds of species of insects, birds, fish, frogs, lizards and mammals that can be predicted with simple mathematical models.

Compiling data from nearly 500 species, scientists with the University of Florida and Oklahoma State University have found the calls of crickets, whales and a host of other creatures are ultimately controlled by their metabolic rates -- in other words, their uptake and use of energy.
"Very few people have compared cricket chirps to codfish sounds to the sounds made by whales and monkeys to see if there were commonalities in the key features of acoustic signals, including the frequency, power and duration of signals," said James Gillooly, Ph.D., an assistant professor in the department of biology at UF's College of Liberal Arts and Sciences and a member of the UF Genetics Institute. "Our results indicate that, for all species, basic features of acoustic communication are primarily controlled by individual metabolism, which in turn varies predictably with body size and temperature. So, when the calls are adjusted for an animal's size and temperature, they even sound alike."
The finding, reported in the Proceedings of the Royal Society B, will help scientists understand how acoustic communication evolved across species, uniting a field of study that has long focused on the calls of particular groups of animals, such as birds.
The results also provide insights regarding common energetic and neuromuscular constraints on sound production, and the ecological and evolutionary consequences of producing these sounds.
"Acoustic signals are used to transfer information among species that is required for survival, growth and reproduction," Gillooly said. "This work suggests that this information exchange is ultimately governed by the rate at which an animal takes up and uses energy."
Animal communication is a long-studied area of biology, going back at least to the days of Aristotle. But generally the studies were species-specific, made in the context of courting calls or parental care of a certain type of animal -- nothing to relate an animal call across a variety of species.
"From my perspective this is one of the first true attempts to provide a general theoretical framework for acoustic communication," said Alexander G. Ophir, Ph.D., an assistant professor of zoology at Oklahoma State, who began the painstaking process of compiling data on animal calls in hundreds of different species while a postdoctoral student at UF. "This seems to provide unifying principles for acoustic communication that can be applied to virtually all species. In terms of producing sounds, we use vocal cords, but other mechanisms of sound production exist, such as insects that rub their legs together. Until now, these sounds have been treated differently. But by providing a general mathematical framework -- a baseline -- we have a reference point to compare those differences.
"So if we say one animal's call is loud, we can provide a predictive reference point to say whether it is truly loud when compared with other animal sounds," he said.
That common reference point can even predict what animals long extinct -- think of Tyrannosaurus rex of "Jurassic Park" fame -- may have truly sounded like.
"These findings say if you give me information about an animal of a certain body size and the mechanisms it uses to make sounds, I can give you a rough idea of what it sounds like," said Jeffrey Podos, Ph.D., an associate professor of biology at the University of Massachusetts Amherst, who did not participate in the study. "It allows us to imagine where the evolution of acoustic signals might go, and where it might have come from. Further study will probably put these principles in a more explicit evolutionary framework, but this is an interesting idea and presented with such a broad view. I can't think of anyone in at least 30 years who has tied together data from such a diversity of species. These authors are really trying to see the forest instead of the trees."

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To a Mosquito, Matchmaking Means 'Singing' in Perfect Harmony

 (Jan. 4, 2010) — Researchers have new insight into the sex lives of the much-maligned mosquitoes that are responsible for the vast majority of malaria deaths, according to a report published online on December 31st in Current Biology, a Cell Press publication.
                                                                                 A new study shows that in finding a partner of the right species type, male and female mosquitoes depend on their ability to "sing" in perfect harmony.
In finding a partner of the right species type, male and female mosquitoes depend on their ability to "sing" in perfect harmony. Those tones are produced and varied based on the frequency of their wing beats in flight.
"Everyone must be familiar with the maddening whine a mosquito makes as it hones in for a bite," said Gabriella Gibson of the University of Greenwich at Medway. "There's no doubt many of us have wondered why it makes its presence so obvious -- surely, after all of these centuries of blood-feeding, selection should have favored a more stealthy approach that would leave mosquitoes less vulnerable to the defensive attacks of its unsettled host. Our findings suggest that mosquitoes rely on the sounds they make to attract a mate of the right species, a behavior that is far more vulnerable to selection than avoiding the risk of being squashed by the rare host that is still awake at feeding time."

The Anopheles gambiae mosquitoes in fact include a considerable amount of genetic diversity, representing a complex of seven species and several chromosomal forms. And that diversity comes with real consequences for humans, explained Gibson and Ian Russell of the University of Sussex. The complexity of malaria epidemiology and control is due in part to the mosquito's remarkable genetic plasticity, enabling its adaptation to a widening range of human-influenced habitats.
The new results help to explain how those different mosquito forms manage to reproductively isolate themselves and maintain that genetic diversity, even while some, including the "M" and "S" forms found in Burkina Faso that were the subject of the current study, can be found traveling together in the very same swarms.
Gibson and Russell's team first discovered that male and female mosquitoes harmonize with each other. Gibson said that this is analogous to two partially deaf singers -- one alto and the other soprano -- who can hear low frequencies, but perhaps not their own or each other's songs. Instead, they listen to the terrible dissonance if one or the other goes a bit sharp or flat, which they can get rid of by adjusting their respective tones until the dissonance diminishes to nothing.

"They can do this even if they each sing a different note, say a 'middle C' and a 'G' four tones higher," Russell said. "By listening and subtly altering their pitch to minimize the dissonance, they achieve their goal of 'singing' in a perfect harmony that we, but not they, can hear."
The researchers have now shown that two mosquitoes don't harmonize successfully if they are of the same sex or if they are not the same type of mosquito. They might try for a while, Gibson explained, but they never find that harmony and eventually give up trying.
And that leads Gibson to another take-home of the study. "Even the most 'lowly creatures,' such as mosquitoes, have highly evolved neurosensory systems that can process relatively simple auditory inputs to produce motor outputs enabling them to distinguish between other types of mosquito that are so closely related we need to analyze their DNA to tell them apart."

The researchers include C. Pennetier, University of Sussex, U.K., University of Greenwich at Medway, Kent, U.K., B. Warren, University of Sussex, U.K.; R. Dabire, Institut de Recherche en Science de la Sante/Centre Muraz, Burkina Faso; I.J. Russell, University of Sussex, U.K.; and G. Gibson, University of Sussex, U.K., University of Greenwich at Medway, Kent, U.K.

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Final Moments of Bee Landing Tactics Revealed

(Jan. 2, 2010) — Landing is tricky: hit the ground too fast and you will crash and burn; too slow and you may stall and fall. Bees manage their approach by monitoring the speed of images moving across their eyes. By slowing so that the speed of the looming landing pad's image on the retina remains constant, bees manage to control their approach. But what happens in the final few moments before touch down? And how do bees adapt to landing on surfaces ranging from the horizontal to upside-down ceilings?

Bees manage their approach by monitoring the speed of images moving across their eyes. By slowing so that the speed of the looming landing pad's image on the retina remains constant, bees manage to control their approach. (Credit: iStockphoto/Amit Erez)

Flies land on a ceiling by simply grabbing hold with their front legs and somersaulting up as they zip along, but a bee's approach is more sedate. Mandyam Srinivasan, an electrical engineer from the Queensland Brain Institute, The University of Queensland and the Australian Research Council's Vision Centre, knew that bees must be doing something different from daredevil flies. Curious to know more about bee landing strategies Srinivasan teamed up with Carla Evangelista, Peter Kraft, and Judith Reinhard from the University of Queensland, and Marie Dacke, visiting from Lund University.

The team used a high-speed camera to film the instant of touch down on surfaces at various inclinations and publish their discoveries about bee landing tactics in The Journal of Experimental Biology on December 28 2009 at http://jeb.biologists.org/.
First the scientists built a bee-landing platform that could be inclined at any angle from horizontal to inverted (like a ceiling), then they trained bees to land on it and began filming. Having collected movies of the bees landing on surfaces ranging from 0deg. to 180deg., and every 10deg. inclination between, Evangelista began the painstaking task of manually analysing the bees landing strategies, and saw that the bees' approach could be broken down into 3 phases.
Initially the bees approached from almost any direction and at any speed, however, as they got closer to the platforms, they slowed dramatically, almost hovering, until they were 16mm from the platform when they ground to a complete halt, hovering for anything ranging from 50ms to over 140ms. When the surface was horizontal or inclined slightly, the bees' hind legs were almost within touching distance of the surface, so it was simply a matter of the bee gently lowering itself and grabbing hold with its rear feet before lowering the rest of the body.

However, when the insects were landing on surfaces ranging from vertical to 'ceilings', their antennae were closest to the surface during the hover phase. The team saw that the antennae grazed the surface and this contact triggered the bees to reach up with the front legs, grasp hold of the surface and then slowly heave their middle and hind legs up too. 'We had not expected the antennae to play a role and the fact that there is a mechanical aspect of this is something that we hadn't thought about,' admits Srinivasan.

Looking at the antennae's positions, the team realised that in the final stages as the insects approached inverted surfaces, they held their antennae roughly perpendicular to the surface. 'The bee is able to estimate the slope of the surface to orient correctly the antennae, so it is using its visual system,' explains Srinivasan. But this is surprising, because the insects are almost completely stationary while hovering and unable to use image movement across the eye to estimate distances. Srinivasan suspects that the bees could be using stereovision over such a short distance, and is keen to test the idea.
Finally the team realised that bees are almost tailor made to land on surfaces inclined at angles of 60deg. to the horizontal. 'When bees are flying fast their bodies are horizontal, but when they are flying slowly or hovering their abdomen tilts down so that the tips of the legs and antennae lie in a plane that makes an angle of 60deg.' explains Srinivasan: so the legs and antennae all touch down simultaneously on surfaces inclined at 60deg. 'It seems like they are adapted to land on surfaces tilted to 60deg. and we are keen to find out whether many flowers have this natural tilt,' says Srinivasan.
Srinivasan is optimistic that he will eventually be able to use his discoveries in the design of novel flight control systems.

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