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Paralympic sprinters’prostheses impair curve-running performance

A Paralympic sprinter. Photo credit: AppliedBiomechanics Lab.

The debate about Paralympic athletescompeting against able-bodied athleteshas raged since before Oscar Pistoriustook to the track on his Flex-FootCheetah prosthetic leg at the LondonOlympics in 2012. Some biomechanistssuggest that prosthetic limbs giveParalympians an unfair advantage, whileothers argued that prostheses restrictathletes as they power away from theblocks. ‘When I saw Paralympians usingthese devices I said, “I really want tounderstand how these prosthesesfunction during sprinting”’, recalls PaoloTaboga, from the University ofColorado, USA. All of the previousstudies had investigated sprinters runningstraight, however, 200 m and 400 mcompetitions are run on curves. ‘Wewanted to see what happens for theseathletes with unilateral [one-sided]amputations when they run on a curve’,explains Taboga, who teamed up withRodger Kram and Alena Grabowski tolearn more about the effects ofprostheses on cornering.

However, instead of testing localrecreational runners, the scientists aimedfor the top and recruited members of theUS and German Paralympic teams. ‘It’slike in Formula 1 races – you push thelimits of cars’, smiles Taboga, whowantedthe athletes to give their prosthetic limbsthe ultimate workout as they sprintedaround a flat curve on an indoor track.

The scientists flew athletes with left andright below-the-knee amputations to the

University of Colorado Boulder, wherethey asked the sprinters to run at topspeed around a 17.2 m radius curve inboth the clockwise and anti-clockwisedirections as they filmed the trials.Taboga admits that running around theclockwise curve was challenging.‘Nobody trains to run in that direction,so it is a bit weird’, he says,remembering that everyone eventuallygot the knack.

However, when the team analysed thesprinters’ performances, they weresurprised to discover that the athletes thatwere running with their prosthesis on theinside of the curve were 4% slower thanthe athletes that were sprinting with theprosthesis on the outside. ‘It was ameasurable difference’, says Taboga,adding that this could add up to two-tenths of a second to a sprint over 200 m.‘That means you could win the race, or getfourth and not even get on the podium’,shrugs Taboga.

Admitting that the extent of theimpairment was unexpected, Tabogaexplains that Paralympic sprintersproduce less force when running straight,which probably means that the force isalso reduced when they go around a bend.In addition, the athletes slowed more asthey took the curve with the affected legon the inside. ‘So you have two limitingfactors that sum up’, he says. And whenhe broke the news to the athletes, Tabogarecalls, ‘A lot of athletes with a left legamputation said, “Oh yes, when I have torun on curves I don’t really like running inlane 1 or 2”’.

But what does all this mean for sprinterscompeting at the next Paralympic Games?Taboga suspects that athletes with a leftleg amputation may be slightlydisadvantaged, although he adds ‘Thecalibre of the athletes is the maindifference’. He suggests, ‘To make a faircompetition, let the left leg amputees runon the outside, lanes 5–8’. And he is keento design new prosthetic limbs that handlecorners better. ‘Then people who don’tnormally like prostheses will use themmore and get more active, improving theirquality of life’, he hopes.

10.1242/jeb.139600

Taboga, P., Kram,R. andGrabowski, A.M. (2016).Maximum-speed curve-running biomechanicsof sprinters with and without unilateral legamputations. J. Exp. Biol. 219, 851-858.

Kathryn Knight

Famished foragers suffermalnutrition faster than fatworkers

Black garden ants (Lasius niger) on a cottonbridge. Photo credit: Audrey Dussutour.

Every family has a picky eater, butimagine feeding a family of 20,000,where some siblings eat nothing but pastaand others expect steak. This is thesituation faced by forager ants on a dailybasis. ‘The queen and larvae want proteinfor growth, but the workers wantcarbohydrates for energy,’ explainsAudrey Dussutour from the University ofToulouse, France. This is fine when foodis plentiful, but Dussutour and hercolleague Stephen Simpson, from theUniversity of Sydney, Australia,wondered how well ant colonies copewhen a staple vanishes from the menu andthey are threatened with starvation.

‘I love collecting ants, it’s like digging fortreasure’, chuckles Dussutour, whoremembers returning from the nearbyvillage of Marquefave with 24 colonies ofblack garden ants (Lasius niger), ready totest their resilience when their dietsbecame unbalanced. Dussutourestablished 64 well-fed mini colonies –with 200 residents each – and thenassigned each colony to one of four diets:a high carbohydrate/low protein diet thatwas perfectly balanced for the ant’snutrition; a poorly balanced diet of lowcarbohydrate and high protein that wouldproduce malnutrition; a dilute well-balanced diet – the ant equivalent of thin

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soup; and a starvation diet. Then shewaited to see how well they fared.

However, Dussutour was in for a shock.‘Usually we use foragers to do these studiesbecause they are supposed to be older sothey are supposed to die earlier’, she says.However, the foragers that were fed theoptimal diet lived for almost as long as theinner nest workers, with one surviving anincredible 409 days while the last workerheld out for 436 days. And some of theforagers on the well-balanced thin soup dieteven survived for 300 days. However, theforagers on the high protein malnutritiondiet struggled, only surviving an average of21 days, and the foragers thatwere placed ona starvation diet were decimated. ‘Theylasted a week and a half, but the inner nestworkers survived for over 100 days’, saysDussutour. So, when their diet took a turnfor the worse, the foragers were always thefirst to die, even though they were thecolony’s sole supplier of nutrition.

But why did the foragers suffer first?Dussutour was puzzled: ‘We wondered ifit was because they had different tasks orif it was because they were different ages’.Foragers are usually the oldest ants in thenest and workers are the youngest, soDussutour used a cunning trick to createyouthful foragers and elderly nest workersto test whether age or role was the cause ofthe forager’s demise. Testing the ants’longevity on a starvation diet, Dussutourwas amazed to discover that the foragersalways died first. ‘Even the foragers thatwere young died earlier than the inner nestworkers that were old’, she says.

Having ruled out age as the cause of theforagers’ deaths, Dussutour wonderedwhether they were more vulnerable tostarvation because they carry less fat thanworker ants. Shemeasured the fat content offoragers’ and workers’ bodies as theyswitched between roles, and no sooner had aworker switched tobecomeaforager than itsbody fat content dropped to 15%.Meanwhile, the fat content of foragers thatassumed a worker’s role rocketed to 30%.‘The colonies that had consumed morecarbohydrates were more fat and we wereable to show that [for ants] the fatter you arethe better it is for your survival,’ chucklesDussutour.

So it seems that lean foragers die first whenfood is scarce, althoughDussutour explainsthat foragers have to be skinny: ‘If they arenot starving, they won’t be motivated to goout to forage’, she laughs.

10.1242/jeb.139576

Dussutour, A., Poissonnier, L.-A., Buhl J. andSimpson, S. J. (2016). Resistance to nutritionalstress in ants: when being fat is advantageous.J. Exp. Biol. 219, 824-833.

Kathryn Knight

Bats have leaky intestineslike birds to fuel flight

Leptonycteris yerbabuenae on Don PanchitoIsland, Mexico. Photo credit: Romeo Saldan a.

No matter how hard a terrestrial animalpushes itself, its exertions are negligible incomparison with those of a hoveringhummingbird. Sustaining metabolic rates(per gram of body mass) that areapproximately 10 times those of elitehuman athletes, hummingbirds directlyfuel their flight muscles with sugar fromtheir nectar diet.WilliamKarasov, from theUniversity of Wisconsin-Madison, USA,and Enrique Caviedes-Vidal, fromUniversidad Nacional de San Luis,Argentina, explain that birds have smallerguts than mammals of the same size, toreduce their cargo costs. However, it alsoturns out that their intestines are leakier –water-soluble nutrients pass through thejunctions between gut cells (in a processknown as paracellular absorption) tocompensate for the smaller surface area– inaddition to using molecules embedded inthe intestine surface to transport nutrientsinto the blood.Could the same hold true forother fliers? ‘The only other livingvertebrates that actively fly are bats’, saysKarasov, so would their intestines be asleaky as those of hummingbirds?

Karasov recalls that Nelly Rodriguez-Peñaarrived in his lab at just the right time to testthe theory. He says, ‘She did a wonderfuljob of identifying a practical, catchablepopulation of bats’, adding that Eddy Pricetaught her how to feed sugar solutions tosmall animals and then collect the minuteblood samples that would be needed todetermine how leaky the bats’ intestines

were. ‘Then she took the method andequipment and set up a makeshift field lab[in Mexico] to do the work’, says Karasov.

Having gently trapped nectar-sippingSaussure’s long-nosed bats in nets at duskas they left their cave roost on DonPanchito Island, Rodriguez-Peña thenworked through the night. First she fed theanimals with a solution made from severalsugars, including L-rhamnose (which canonly enter the bat’s bloodstream byparacellular absorption because there areno protein transporters to carry the sugaracross the intestine wall) and D-(+)-cellobiose (a large sugar that alsoenters the bloodstream by paracellularabsorption, but at a slower rate). Then shepatiently collected minute blood samples(28 μl) from the animals over a 2 h period.After releasing the bats, Rodriguez-Peñarelocated to Cesar Flores-Ortiz’s lab at theUniversidad Nacional Autonoma deMéxicowith the blood samples to find outhow much of each sugar was in the bats’blood.

Using high-performance liquidchromatography to analyse the bloodsamples, Rodriguez-Peña saw therhamnose levels increased substantially;the intestines were leaky and the animalswere using paracellular routes to absorbsugar into the blood. And when shemeasured the amount of cellobiose in theblood samples, she found that themoleculealso crossed the intestine, but atmuch lowerlevels. ‘It [the junction between adjacentintestine wall cells] is almost like a filter,and ifmolecules are too big they cannot getthrough; that is what makes the junctiontight against large foreign molecules’,explains Karasov. In fact, the junctionswere so leaky that almost as muchrhamnose appeared in the bats’blood as if ithad been injected directly.

So hovering nectar-feeding bats use thesame leaky intestine mechanism ashummingbirds to absorb as much sugar aspossible into the blood to meet theirimmense metabolic demands. Karasovsays, ‘I don’t know if this is aphenomenon of small bats and smallbirds, or all bats and birds, so we need tostudy some really big bats next’.

10.1242/jeb.139584

Rodriguez-Pena, N., Price, E. R., Caviedes-Vidal,E., Flores-Ortiz C. M. and Karasov, W. H.(2016). Intestinal paracellular absorption isnecessary to support the sugar oxidationcascade in nectarivorous bats. J. Exp. Biol. 219,779-782.

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Prozac makes Siamese fighting fish timid

Hailed as a wonder drug since the mid-1980s, fluoxetine – the drug in Prozac – ison the World Health Organisation List ofEssential Medicines. Used to treat humanpsychiatric disorders such as depressionand post-traumatic stress disorder,fluoxetine is believed to increase levels ofthe neurotransmitter serotonin in thesynapse between nerves by reducingreabsorption into nerve cells to relievesymptoms. But humans may not be theonly animals on the doctor’s prescription.Teresa Dzieweczynski and colleaguesfrom the University of New England,USA, explain that the drug is turning up inour river systems, thanks to its resistanceto breakdown, and seems to be affectingthe behaviour of aquatic residents,reducing aggression and risk-taking, andaffecting how often animals feed. Butlittle is known about the longer-termeffects of exposure or how the drug mayalter behaviour in different settings. Asfemale Siamese fighting fish are known to

be less aggressive and inquisitive after adose of the drug, Dzieweczynski and hercolleagues Brennah Campbell and JessicaKane decided to find out how maleSiamese fighting fish that had not beenexposed to the fluoxetine and those thathad experienced a week-long low(0.5 μg l−1 – similar to the levels found ineffluent water) or high dose (5 μg l−1 –similar to levels found in body fluids ofhuman patients) of fluoxetine respondedto situations that were designed tochallenge their courage, and how theirreactions changed over time.

Right from the start, it was clear that fishthat had not been exposed to fluoxetinewere much keener to explore a novelempty tank than the fish that had beenswimming in water laced with the anti-depressant, and the fish that had receivedthe highest dose were the most timid.However, the fish that had been exposedto 0.5 μg l−1 of the drug were bolder on

some occasions than others. And whenthe team tested the fish’s reactions to anunfamiliar tank furnished with intriguingstones and plants, or the presence of ashoal of lady Siamese fighting fish, thetwo sets of drugged males were equallydisinterested in exploring; the strength ofthe drug did not affect them differently.The team says, ‘Perhaps most importantlyand alarmingly, the effects of exposurelasted even after fluoxetine was removed’,and they warn, ‘Even brief periods ofexposure could potentially producechronic effects, especially as boldness isimportant in migration, aggression andpredator evasion’.

10.1242/jeb.139592

Dzieweczynski, T. L., Campbell, B. A. and Kane,J. L. (2016). Dose-dependent fluoxetine effectson boldness in male Siamese fighting fish. J. Exp.Biol. 219, 797-804.

Kathryn Knightkathryn.knight@biologists.com

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