Journal of Experimental Biology

Kathryn, Knight,

doi: 10.1242/jeb.047878pmid: N/A

When a fruit fly selects a target, the insect locks it in its sight (fixates) and homes in. ‘But less was known about what happens when they actually reach those objects,’ explains Alice Robie from the California Institute of Technology. Explaining fixation, Robie's supervisor, Michael Dickinson, says, ‘It is often described as what happens when you hang a carrot in front of a donkey and it keeps following the carrot forever. We were curious about what happens when the “donkey” actually gets to the carrot. Andrew Straw in my lab has been working on developing software that allows us to track flies with high accuracy so we had the technology to allow us to see how the flies explore a simple but interesting landscape under conditions where we could know their position and velocity at all times’ (p. 2494 ). But first Robie and Dickinson had to design their landscape. Filming the insects' movements from a single position, the duo settled on a landscape of cones arranged in an arena so that they could always see the fly's position and calculate the insect's vertical position as it scaled the heights. Robie built 4 cones ranging from 36 mm to 10 mm high each with the same surface area but with sides ranging from a steep 75 deg slope to a shallow 30 deg slope. Then she released individual flies, which were hungry and so highly motivated to explore their surroundings, into the arena and filmed them for 10 min in infra-red light. Robie was instantly struck that the flies explored all four cones equally, but once they'd found the highest cone they scaled it and spent more time there than on the shorter shallower cones. ‘We were surprised that they showed such a strong preference for the tallest, steepest object,’ says Dickinson. Curious to know how the insects identified the tallest cone, Robie switched off the lights and filmed them with infra-red light to see how they coped in the dark. Without their sight, the flies could no longer fixate on the cones, so their paths became more wiggly as they explored the arena, but once they had stumbled upon the highest cone they reacted as if the lights were on, scaled it and stopped at the top. The insects were using some sense other than vision to identify the tallest cone. Knowing that the insects sense gravity with sensors in their antennae (Johnston's organs) Robie wondered if the insects could use these gravity sensors to identify the steepest (and highest) cone. Putting a dab of glue on the joint between the second and third antennal segments to inactivate the Johnston's organs, Robie waited to see if the insect could identify the tallest cone by vision alone. Again the fly succeeded. Finally, Robie decided to see whether a fly deprived of sight and its gravity sensors could identify the tallest cone, but this time it could not. ‘The movie was extraordinary,’ says Dickinson, ‘they would go up the cone over the top and down the other side. It was like they just didn't know they were on an object.’ Dickinson admits that he was surprised that the flies were unable to identify the tallest cone when deprived of both senses. He says, ‘The animal is covered with mechano receptors, especially on the legs, so we were almost certain that they could use information from their legs to tell them they are on a steep object.’ However, having convinced himself that fruit flies only require two senses to identify steep slopes, Dickinson is keen to find out more about the neural circuits that control how flies explore their environment. References Robie A. A. , Straw A. D. , Dickinson M. H. ( 2010 ). Object preference by walking fruit flies, Drosophila melanogaster, is mediated by vision and graviperception , J. Exp. Biol. 213 , 2494 - 2506 . Google Scholar Crossref Search ADS © 2010. 2010

Kathryn, Knight,

doi: 10.1242/jeb.047845pmid: N/A

View large Download slide View large Download slide Jumping spiders are famed for having up to four pairs of eyes. Together, the eyes comprise a modular visual system that gives the spider a good view of the world. But how does each pair of eyes contribute to the arthropod's vision? Explaining that the second pair of eyes (anterior lateral eyes) flank the central pair, Daniel Zurek and his colleagues from Macquarie University, Australia, wondered whether Servaea vestita spiders use the second pair of eyes to identify movement in the environment and to decide whether or not to orient towards it (p. 2372 ). Covering four of the spiders' eyes with removable silicone blinds, the team showed them tethered live flies and movies of moving dots and tested the partially sighted arthropods' responses to the movements. The team also compared the responses of fully fed and hungry females with those of fully fed and hungry males, to see whether hunger motivated the spiders to orient in the direction of passing potential meals. Analysing the partially sighted arthropods' responses, the team found that they could stalk and attack flies using their anterior lateral eyes alone. The spiders also oriented in the direction of fly sized dots moving at a walking pace, but ignored large fast dots that could have been hungry predators and small slow dots that resembled insects that were too small for the arthropods to eat. And when the team compared the males' and females' responses, the females were far more motivated to orient than the males, probably because their energy demands are higher. Zurek says, ‘Even when the spiders were confined to visual input from this secondary pair of eyes, they could respond to targets that are very hard for other animals to see, and were able to detect, stalk and attack flies, which was unexpected.’ References Zurek D. B. , Taylor A. J. , Evans C. S. , Nelson X. J. ( 2010 ). The role of the anterior lateral eyes in the vision-based behaviour of jumping spiders . J. Exp. Biol. 213 , 2372 - 2378 . Google Scholar Crossref Search ADS © 2010. 2010

Kathryn, Knight,

doi: 10.1242/jeb.047852pmid: N/A

View large Download slide View large Download slide The larva of Diabrotica virgifera virgifera beetles wreak havoc on maize. Feasting on the plants' roots, they are estimated to cause $1 billion of damage every year in the US. Ted Turlings from the University of Neuchâtel, Switzerland, explains that the pest, known as western corn rootworm, only arrived in Serbia in the 1990s, but since then it has marched through at least 11 European countries. ‘Pesticides work to control the pest, but they are not environmentally friendly,' explains Turlings and adds, ‘When it arrived in Germany in 2007 they wanted to eradicate it but the pesticide that they used killed millions of bees.’ Looking for an alternative, more ecological, form of pest control, Turlings wondered whether predatory nematodes (microscopic worms) that munch on insects could defeat the pest. Knowing that Heterorhabditis bacteriophora , which kills western corn rootworm larvae, is relatively unresponsive to an alarm signal, ( E )-β-caryophyllene, released by the infested roots, Turlings wondered whether he could improve H. bacteriophora 's response to caryophyllene in a bid to produce an effective biopesticide (p. 2417 ). Using an ‘olfactometer’ (six tubes radiating out from a central point) packed with damp sand for the nematodes to crawl through, Ivan Hiltpold inserted capillaries into the sand, which released different odours at the end of three of the olfactometer's arms. Then he released H. bacteriophora nematodes at the centre of the olfactometer and allowed the nematodes to choose which odour they tracked. Timing how long it took 500 nematodes to reach the end of the trail in the caryophyllene arm of the olfactometer, Hiltpold collected the worms and allowed them to breed. Gathering the offspring 10 days later, he tested their responses to the three odours and again selected the 500 nematodes that reached the end of the caryophyllene trail first for breeding. Repeating the selection process 6 times, Hiltpold improved the nematode's performance significantly, decreasing the time it took 500 worms to reach the end of the caryophyllene trail from 10 h to 2 h. Next Hiltpold tested how improving the nematode's response to caryophyllene had impacted on their potency. Sprinkling the selected nematodes directly on the pest larvae and waiting to see how many larvae died, he was relieved to find that the selected nematodes were only slightly less infectious than their forebears. This loss of potency could be overcome easily by the worm's increased response to caryophyllene, but how would the selected nematodes perform in a field? ‘We couldn't test the nematodes in Switzerland because the western corn rootworm is not present yet, so we had to travel to Hungary,’ says Turlings. Teaming up with Stefan Toepfer and Ulrich Kuhlmann from CABI Europe-Switzerland, who had access to western corn rootworm infected fields sown with two varieties of maize (one that produced caryophyllene and another that did not), Turlings' colleague, Mariane Baroni, sprayed solutions of the selected nematodes between the rows of maize in some plots and sprayed solutions of the unselected nematodes on other plots in the same fields. Then the team waited to see whether the selected nematodes offered any protection against the pest. They did. The variety of maize that released caryophyllene was healthier than the variety that did not release caryophyllene after treatment with the selected nematodes; and the selected nematodes killed more pest larvae near the caryophyllene releasing maize than the unselected nematodes did. Turlings says that this result is encouraging, but admits that there is more to be done before the nematodes can be used commercially. For instance, US varieties of maize have lost the caryophyllene alarm signal and application of the biopesticide is costly and problematic, but Turlings is optimistic that his team can crack both of these problems to add the nematodes to the maize farmer's arsenal. References Hiltpold I. , Baroni M. , Toepfer S. , Kuhlmann U. , Turlings T. C. J. ( 2010 ). Selection of entomopathogenic nematodes for enhanced responsiveness to a volatile root signal helps to control a major root pest . J. Exp. Biol. 213 , 2417 - 2423 . Google Scholar Crossref Search ADS © 2010. 2010

Kathryn, Knight,

doi: 10.1242/jeb.047860pmid: N/A

Despite their nocturnal and aerial lifestyle, bats are still at risk from predators. Weasels and stoats can scale the walls of bat roosts and young and old bats are in danger from foxes if they fall. Tess Driessens from Vrije Universiteit Brussels, Belgium, and Björn Siemers from the Max Planck Institute for Ornithology, Germany, wanted to know how bats recognise predators. ‘It might be important for bats to assess whether or not predators are there when they inspect new roosts,’ explains Driessens. While sound and visual cues could be helpful warnings when predators are in residence, they are of little help if a predator is absent when a bat investigates a new roost. However, odours can linger long after a predator has departed. Curious to find out whether bats react to odours left by potential predators, Driessens and Siemers decided to find out whether bats fear odours left by foxes, weasels and stoats (p. 2453 ). View large Download slide View large Download slide ‘Synthetic predator odours such as TMT [found in fox faeces] and 2-PT [found in weasel and stoat odours] induce innate fear responses in rodents so we decided to use these synthetic olfactory cues and the odour of a natural least weasel to compare bat responses,’ explains Driessens. Travelling to the Max Planck Institute's Tabachka Bat Research Station in Bulgaria, Driessens and Siemers collected greater mouse-eared bats as they returned to their cave after a night of foraging. The duo then took the animals to the lab to test their sense of smell before releasing the animals back at their roost. Putting individual bats in a Y-shaped maze, Driessens placed a cotton pad that carried the scent of either a least weasel, 1.8×10 −2 mol l −1 TMT or 1.8×10 −4 mol l −1 2-PT in one arm of the maze and a cotton pad soaked with the odourless solvent (DEP – used to dissolve TMT and 2-PT) in the other arm. Then she filmed the bat's behaviour for 8 min, recording and scoring the animal's activity levels and whether it avoided the predator's odour. Cleaning the maze with ethanol so that no trace of the smell was left, Driessens then tested the bat's response to an equally unpleasant odour, either basil extract or goat smell, which does not terrify rodents, to see if the bats were just avoiding the smell because they didn't like it, or they avoided it because it terrified them. If the bat was frightened by the fox and weasel scents, Driessens expected it to become inactive and avoid the TMT or 2-PT arm of the maze, while remaining active in the maze when the acrid odour was around. But after testing the bats, Driessens found that they did not respond differently to the two types of odour. They remained equally active in both experiments and were happy to visit both arms of the predator maze. The bats weren't bothered by the predators' smells. So why didn't the greater mouse-eared bats avoid fox and weasel odours when encounters with either animal could prove fatal? Initially the duo was concerned that the bats couldn't smell the predator odours in the maze. However, when they considered the bat's olfactory threshold, which is similar to that of humans, and tested the smells on colleagues – who regularly work in smelly bat caves and had no problem picking up the stench – they were convinced that the bats must have been able to smell the odours. Driessens suspects that the bats may be ignoring the odours because they have other more pressing concerns than predation when choosing a roost. Alternatively, bats could be so familiar with the odours of cohabiting weasels and foxes that they no longer perceived the odours as a threat. References Driessens T. , Siemers B. M. ( 2010 ). Cave-dwelling bats do not avoid TMT and 2-PT – components of predator odour that induce fear in other small mammals . J. Exp. Biol. 213 , 2453 - 2460 . Google Scholar Crossref Search ADS © 2010. 2010

Laura, Hausmann,;Martin, Singheiser,;Hermann, Wagner,

doi: 10.1242/jeb.034231pmid: 20581263

View large Download slide Laura Hausmann, Martin Singheiser and Hermann Wagner discuss Roger Payne's 1971 paper entitled: Acoustic Location of Prey by Barn Owls ( Tyto alba ). A copy of the paper can be obtained from http://jeb.biologists.org/cgi/content/abstract/54/3/535 View large Download slide Laura Hausmann, Martin Singheiser and Hermann Wagner discuss Roger Payne's 1971 paper entitled: Acoustic Location of Prey by Barn Owls ( Tyto alba ). A copy of the paper can be obtained from http://jeb.biologists.org/cgi/content/abstract/54/3/535 In 1971, Roger Payne published the paper ‘Acoustic Location of Prey by Barn Owls ( Tyto alba )’. Payne had conducted the underlying experiments at Cornell University in partial fulfilment of the requirements for his PhD, which he obtained in 1961. When the paper was published, Payne, a zoologist, was a professor at Rockefeller University. By that time he was already famous for his discovery of songs in humpback whales. Payne later left academia and started to promote conservation of whales, an activity he still pursues today. Despite this extraordinary career, Payne took the time to write the paper on the location of prey by the barn owls. This paper laid the ground for many subsequent studies on the barn owl's ability to catch prey in complete darkness, specifically on the auditory processing involved in this behaviour. In the 1960s, model systems such as bats, electric fish and song birds were just emerging. Payne was attracted by the specific anatomical adaptations of the barn owl and started his paper with a note on the asymmetrically arranged ears and nocturnal lifestyle of owls. Others had noted these specializations before, but Payne was not convinced by the existing hypotheses that related the asymmetrically arranged ears, the ruff and the nocturnal lifestyle to possible acoustic mechanisms underlying the location of prey by barn owls. After describing the anatomy of the ear in detail, Payne reports an experiment to determine possible sensory cues that the owls could use for sound localization. In this experiment the barn owl first learned to strike live mice in complete darkness in a free-flight room, the floor of which was covered with a layer of dry leaves. Sometimes a mouse-sized wad of paper was dragged on the floor instead of a mouse. The owl successfully struck this artefact, thus excluding both visual and infrared detection as the crucial cues to locating its prey. Since the paper also did not smell like any prey, Payne concluded that the owls must use auditory cues. He, and later Mark Konishi ( Konishi, 1973 ), also confirmed this conclusion by letting the mouse tow a rustling piece of paper. Guess what, the barn owl struck the paper and not the quietly walking mouse. After this initial clarification that owls hunt using acoustic cues, Payne tested the geometrical parameters underlying prey capture such as distance, motion direction and horizontal and vertical angles. He took motion pictures of an animal flying in total darkness. The camera triggered a stroboscope that produced infra-red flashes. By analysing the film sequences Payne found out that the owls flew slower in darkness than they did in light. Payne also observed that the owl ‘whirled’ its head towards a sound source, a fixation response that occurs before the owl flies at the mouse. Payne also analysed striking precision by measuring the impact of the talons on the floor, demonstrating that the owl could locate a sound-emitting target within approximately 1 to 3 deg in both the horizontal and vertical directions. Later on, the head-fixation behaviour was quantified with magnetic tracking systems revealing a similar precision. Payne's experiments did not lead to a firm conclusion about the ability of the owl to discriminate distances by listening to sound emitted by a loudspeaker, and this issue is not resolved as of today. On the other hand, Payne observed that the long axis of the barn owl's talons' oval strike pattern was parallel to the long axis of the mouse. Thus, the barn owl might extract information about the mouse's motion direction from acoustic information. Again, the issue of passive acoustic motion-direction detection is still a matter of debate today. The experiments described so far did not reveal which sound parameters the barn owl uses for sound localization. Payne specifically tested the influence of frequency on localization behaviour. Sound frequencies above 5 kHz seemed to be most important. To quantify how this frequency dependence may be related to the asymmetrically arranged ear openings, Payne measured the directional sensitivities of the barn owl's ears. This method of using so-called head-related transfer functions is now the basis for many quantitative experiments ( Keller et al., 1998 ). Payne had already related the increased precision at frequencies above 5 kHz to the more complex directional-sensitivity patterns measured at the ear drum in this frequency region. He also considered intracranial sound transmission, effectively asking the question of whether the owl's ears work as a pressure receiver or as a pressure-difference receiver. This question is also still unresolved, although the existing evidence clearly favours the pressure receiver. Finally, Payne measured cochlear microphone potentials. He used the owls' sensitivity as a rough estimate of their hearing range. Payne himself summarized his findings by stating that ‘barn owls ( Tyto alba ) can locate prey in total darkness using only the sense of hearing’. The error in both the vertical and horizontal planes is between 1 and 3 deg and frequencies above 5 kHz are particularly important for owls to locate their prey. This short review may demonstrate that Payne asked many important questions and opened several fields of research by his experiments. The only approach that Payne did not try was to record neural activity from the barn owl's brain. However, Payne's experiments pointed towards the questions to be asked in such experiments. For example, electrophysiological recordings by Moiseff and Konishi ( Moiseff and Konishi, 1981 ) demonstrated that the owl is able to use the interaural time difference at frequencies above 5 kHz for azimuthal sound localization. This came as a surprise, because it was thought at that time that the use of interaural time difference from the carrier was limited to frequencies below 4 kHz. Many laboratories continue to use the barn owl as a model system for neuroethological research as well as for basic questions in neuroscience, such as plasticity in neural systems. Whereas the barn owls' free-flight behaviour had received little attention in three decades following Payne's paper, several recent studies have used modern technology to analyse the owl's prey capture in controlled free-flight experiments ( Fux and Eilam, 2009 ; Hausmann et al., 2009 ; Singheiser et al., 2010 ). The questions asked in these papers and many others may be traced back to Payne's classic experiments. A next step forward in owl research would be to create a transgenic owl so that the advantages of manipulating genes that have made mouse research so successful can be used to study the genetic basis of the underlying specific anatomical adaptations. Payne's paper almost reads like a novel, at no expense to its high scientific quality. Payne performed hypothesis-driven experiments and presents a clear line of argument based on his observations. This work has inspired our research on owl's localization behaviour. The work by Roger Payne certainly has the potential to inspire future generations of researchers. REFERENCES Fux M. , Eilam D. ( 2009 ). The trigger for barn owl (Tyto alba) attack is the onset of stopping or progressing of prey . Behav. Processes 81 , 140 - 143 . Google Scholar Crossref Search ADS Hausmann L. , Plachta D. T. T. , Singheiser M. , Brill S. , Wagner H. ( 2009 ). In-flight corrections in free-flying barn owls (Tyto alba) during sound localization tasks . J. Exp. Biol. 211 , 2976 - 2988 . Google Scholar Crossref Search ADS Keller C. H. , Hartung K. , Takahashi T. T. ( 1998 ). Head-related transfer functions of the barn owl: measurement and neural responses . Hear. Res. 118 , 13 - 34 . Google Scholar Crossref Search ADS Konishi M. ( 1973 ) How the owl tracks its prey . American Scientist 61 , 414 - 424 . Google Scholar Moiseff A. , Konishi M. ( 1981 ) Neuronal and behavioral sensitivity to binaural time differences in the owl , J. Neurosci. 1 , 41 - 49 . Google Scholar Crossref Search ADS Payne R. S. ( 1971 ). Acoustic Location of Prey by Barn Owls (Tyto alba) . J. Exp. Biol. 54 , 535 - 573 . Google Scholar Singheiser M. , Plachta D. T. T. , Brill S. , Bremen P. , van der Willigen R. F. , Wagner H. ( 2010 ). Target-approaching behavior of barn owls (Tyto alba): influence of sound frequency . J. Comp. Physiol. A 196 , 227 - 240 . Google Scholar Crossref Search ADS © 2010. 2010

Vincent, Fourcassié,;Audrey, Dussutour,;Jean-Louis, Deneubourg,

doi: 10.1242/jeb.031237pmid: 20581264

Many animals take part in flow-like collective movements. In most species, however, the flow is unidirectional. Ants are one of the rare group of organisms in which flow-like movements are predominantly bidirectional. This adds to the difficulty of the task of maintaining a smooth, efficient movement. Yet, ants seem to fare well at this task. Do they really? And if so, how do such simple organisms succeed in maintaining a smooth traffic flow, when even humans experience trouble with this task? How does traffic in ants compare with that in human pedestrians or vehicles? The experimental study of ant traffic is only a few years old but it has already provided interesting insights into traffic organization and regulation in animals, showing in particular that an ant colony as a whole can be considered as a typical self-organized adaptive system. In this review we will show that the study of ant traffic can not only uncover basic principles of behavioral ecology and evolution in social insects but also provide new insights into the study of traffic systems in general.

E., Pettex,;F., Bonadonna,;R., Enstipp, M.;F., Siorat,;D., Grémillet,

doi: 10.1242/jeb.042267pmid: 20581265

Seabirds, as other marine top predators, are often assumed to forage in an unpredictable environment. We challenge this concept and test the hypothesis that breeding Northern gannets (Morus bassanus) anticipate the spatio–temporal occurrence of their prey in the English Channel. We analyzed 23 foraging tracks of Northern gannets breeding on Rouzic Island (Brittany) that were recorded using GPS loggers during 2 consecutive years. All birds commuted between the breeding colony and foraging areas located at a mean distance of 85 km and 72 km (in 2005 and 2006, respectively) from the colony. Mean linearity indices of the outbound and inbound trips were between 0.83 and 0.87, approaching a beeline path to and from the foraging area. Additional parameters (flight speed, and number and duration of stopovers at sea) for the outbound and inbound trip were not statistically different, indicating that birds are capable of locating these feeding areas in the absence of visual clues, and to pin-point their breeding site when returning from the sea. Our bearing choice analysis also revealed that gannets anticipate the general direction of their foraging area during the first 30 min and the first 10 km of the trip. These results strongly suggest that birds anticipate prey location, rather than head into a random direction until encountering a profitable area. Further investigations are necessary to identify the mechanisms involved in seabird resource localization, such as sensorial abilities, memory effects, public information or a combination of these factors.

B., Zurek, Daniel;J., Taylor, Alan;S., Evans, Christopher;J., Nelson, Ximena

doi: 10.1242/jeb.042382pmid: 20581266

Jumping spiders, or salticids, sample their environment using a combination of two types of eyes. The forward-facing pair of ‘principal’ eyes have narrow fields of view, but exceptional spatial resolution, while the two or three pairs of ‘secondary’ eyes have wide fields of view and function especially well as motion analysers. Motion detected by the secondary eyes may elicit an orienting response, whereupon the object of interest is examined further using the high-acuity principal eyes. The anterior lateral (AL) eyes are particularly interesting, as they are the only forward-facing pair of secondary eyes. In this study, we aimed to determine characteristics of stimuli that elicit orienting responses mediated by the AL eyes. After covering all eyes except the AL eyes, we measured orienting responses to dot stimuli that varied in size and contrast, and moved at different speeds. We found that all stimulus parameters had significant effects on orientation propensity. When tethered flies were used as prey, we found that visual information from the AL eyes alone was sufficient to elicit stalking behaviour. These results suggest that, in terms of overall visual processing, the relevance of spatial vision in the AL eyes has been underestimated in the literature. Our results also show that female spiders are significantly more responsive than males. We found that hunger caused similar increases in orientation propensity in the two sexes, but females responded more often than males both when sated and when hungry. A higher propensity by females to orient toward moving objects may be related to females tending to experience higher nutritional demands than males.

D., Clark, T.;T., Brandt, W.;J., Nogueira,;E., Rodriguez, L.;M., Price,;J., Farwell, C.;A., Block, B.

doi: 10.1242/jeb.043455pmid: 20581267

Specific dynamic action (SDA) is defined as the energy expended during ingestion, digestion, absorption and assimilation of a meal. This study presents the first data on the SDA response of individual tunas of any species. Juvenile Pacific bluefin tunas ( Thunnus orientalis ; body mass 9.7–11.0 kg; N =7) were individually fed known quantities of food consisting primarily of squid and sardine (meal energy range 1680–8749 kJ, ~4–13% of tuna body mass). Oxygen consumption rates ( ) were measured in a swim tunnel respirometer during the postprandial period at a swimming speed of 1 body length ( BL ) s −1 and a water temperature of 20°C. was markedly elevated above routine levels in all fish following meal consumption [routine metabolic rate (RMR)=174±9 mg kg −1 h −1 ]. The peak during the SDA process ranged from 250 to 440 mg kg −1 h −1 (1.5–2.3 times RMR) and was linearly related to meal energy content. The duration of the postprandial increment in ranged from 21 h to 33 h depending upon meal energy content. Consequently, the total energy used in SDA increased linearly with meal energy and ranged from 170 kJ to 688 kJ, such that the SDA process accounted for 9.2±0.7% of ingested energy across all experiments. These values suggest rapid and efficient food conversion in T . orientalis in comparison with most other fishes. Implanted archival temperature tags recorded the increment in visceral temperature ( T V ) in association with SDA. returned to routine levels at the end of the digestive period 2–3 h earlier than T V . The qualitative patterns in and T V during digestion were similar, strengthening the possibility that archival measurements of T V can provide new insight into the energetics and habitat utilization of free-swimming bluefin in the natural environment. Despite efficient food conversion, SDA is likely to represent a significant component of the daily energy budget of wild bluefin tunas due to a regular and high ingestion of forage.

M., Burrows,;D., Picker, M.

doi: 10.1242/jeb.042192pmid: 20581268

Pygmy mole crickets live in burrows at the edge of water and jump powerfully to avoid predators such as the larvae and adults of tiger beetles that inhabit the same microhabitat. Adults are 5–6 mm long and weigh 8 mg. The hind legs are dominated by enormous femora containing the jumping muscles and are 131% longer than the body. The ratio of leg lengths is: 1:2.1:4.5 (front:middle:hind, respectively). The hind tarsi are reduced and their role is supplanted by two pairs of tibial spurs that can rotate through 180 deg. During horizontal walking the hind legs are normally held off the ground. Jumps are propelled by extension of the hind tibiae about the femora at angular velocities of 68,000 deg s −1 in 2.2 ms, as revealed by images captured at rates of 5000 s −1 . The two hind legs usually move together but can move asynchronously, and many jumps are propelled by just one hind leg. The take-off angle is steep and once airborne the body rotates backwards about its transverse axis (pitch) at rates of 100 Hz or higher. The take-off velocity, used to define the best jumps, can reach 5.4 m s −1 , propelling the insect to heights of 700 mm and distances of 1420 mm with an acceleration of 306 g . The head and pronotum are jerked rapidly as the body is accelerated. Jumping on average uses 116 μJ of energy, requires a power output of 50 mW and exerts a force of 20 mN. In jumps powered by one hind leg the figures are about 40% less.