Reeve, M A

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OUTSIDE JEBSome like it hotter thanothersEXTREME PHYSIOLOGYIf you want to meet a truly tough fish, buya ticket to Lake Magadi, Kenya. Here, theMagadi tilapia swim happily in the hot,alkaline waters of the lake, where oxygenlevels soar and plummet daily and waterchemistry pushes the boundaries of acid–base regulation. Few fish can survive suchan extreme aquatic environment and thishas attracted comparative physiologistsfor decades to the town of Magadi, wheretilapia are easily studied in the nearbyman-made lagoon. But not all Magaditilapia are created equal, as discovered byCanadian scientist ChrisWood and a teamof international colleagues on a recentexpedition to Kenya. In fact, life is evenmore challenging in the fast-flowing hotsprings that feed into Lake Magadi’ssouthwestern shores. Remarkably, tilapialive here too.Wood and crew trekked out to study thisisolated population of Magadi tilapia,looking for the toughest tilapia yet. Theynoted some striking differences betweenthe deep, static waters of the lagoon andthe shallow, steamy waters of the hotsprings. For example, in a given 24 hperiod, the lagoon tilapia endure animpressive swing in dissolved oxygenlevels from ∼15% to 80% saturation, buttheir hot spring relatives eat breakfast inanoxia and lunch in super-saturatedwater! Also, during that same 24 hperiod, while the lagoon fish sweat it outin 33–36oC water, over in the hotsprings, the tilapia’s mercury peaks at awhopping 43oC and fluctuates by 11oCthroughout the day. So a day in the lifeof a hot springs tilapia is no small feat,and Wood bet that these fish must haveoutstanding thermal tolerance andmetabolic capacity.Wood’s study started heating up whenhe measured the upper criticaltemperatures of the lagoon and hotsprings tilapia. When the researcherscranked the thermostat on the lagoonfish, they held out to a maximumtemperature of 44.5oC – that’s prettytoasty for a poikilotherm. But the hotsprings fish toughed out temperatures to45.6oC, the highest temperature everrecorded for any fish! Scarily, the hotsprings fish died at a temperature thatwas only 2.6oC warmer than that inwhich they swim daily and that gap willquickly narrow if current climate changetrends continue.Next, Wood and his team beganmeasuring the routine and maximummetabolic rates of fish from the two LakeMagadi habitats and again the hot springstilapia set records. While routinemetabolic rate in all Magadi tilapia ishigh, the fish Wood’s team caught fromthe hot springs had metabolic rates thatwere quadruple the rate of the lagoon fish,putting them on a par with mammals of acomparable size. And, when they madethe fish swim to exhaustion to measuretheir maximum metabolic rates, not onlydid the hot springs tilapia outperform thelagoon fish in the swim test, theirmaximum metabolic rate surpassed anypreviously recorded in a size-matchedfish.The Magadi tilapia remains a perfect fishfor studying physiological adaptations toextreme environments and the hot springspopulation teeters on the edge of thatextreme, making them true Olympiansamong aquatic athletes!10.1242/jeb.130310Wood, C. M., Brix, K. V., De Boeck, G., Bergman,H. L., Bianchini, A., Bianchini, L. F., Maina,J. N., Johannsson, O. E., Kavembe, G. D.,Papah, M. B., Letura, K. M. and Ojoo, R. O.(2016). Mammalian metabolic rates in the hottestfish on earth. Sci. Rep. 6, 26990.Sarah AldermanUniversity of Guelphalderman@uoguelph.caLeaf-footed bugs chooseto lose legsAUTOTOMYFor animals, the ability to escape fromlife-threatening situations is essential.Whether fleeing from a predator’s grasp,or manoeuvring their way out of a fight,animals benefit from traits that allow themto escape more easily. One such traitfound throughout the animal kingdom isautotomy: the ability to voluntarily shedan appendage, most commonly a leg ortail. This may seem like an extremesolution, but in instances where the choiceis to lose a limb or lose your life, it’s a no-brainer.Autotomy is particularly commonamongst invertebrates, with variousinsects, arachnids and crustaceans allreported to have the ability to self-amputate. Depending on the species, andoften the animal’s age, these lost legs mayeither grow back, or the individual mayhave to cope without it for the remainderof their life. However, considering thatautotomy is such an extreme behaviourwith potentially severe consequences, westill don’t really know which speciesresort to autotomy, particularly withininsects.To try to bridge this gap, a team ofresearchers from the University of Floridafocused their efforts on the Coreidaefamily of insects, better known as the leaf-footed bugs. Led by Zachary Emberts,they first looked at the frequency of legloss within natural populations of ninespecies of this insect. By collecting adultleaf-footed bugs and noting if legs werelost, the team observed that depending onthe species, between 7.9% and 21.5% ofOutside JEB is amonthly feature that reports themost exciting developments in experimental biology. Articles that have been selected andwritten by ateam of active research scientists highlight the papers that JEB readers can’t afford to miss.2968© 2016. Published by The Company of Biologists Ltd | Journal of Experimental Biology (2016) 219, 2968-2970JournalofExperimentalBiologyindividuals had legs missing. In addition,they looked at which legs were absent andsaw that there appeared to be a largerproportion of hind legs missing.Interestingly, the hind legs of many ofthese species of leaf-footed bug are highlydecorated, have enlarged femurs and areoften used as weapons when fighting overmates.Finding individuals with missing legsdoes not, however, prove that the speciescan autotomise, so to test this, theresearchers attempted to induce autotomyin the lab by grasping a hind leg withforceps to simulate attack from a predator.Supporting the field results, all ninespecies successfully autotomised the leg.The authors noted that all of the breakagesoccurred at the same leg joint and wereaccompanied by a stereotypical ‘raise-and-drop’ movement of the abdomen.Intriguingly, in three species, theyobserved that only femalesautotomised the limb, despite thepresence of male individuals with missinglegs in the wild.This work has helped to broaden ourknowledge of the range of thisextraordinary trait in insects, but has alsoraised some questions. In some species ofleaf-footed bug, the hind leg is used as adecoy during attacks, distracting predatorswith its decoration, and here the ability toshed it quickly makes great sense.However, these insects also often usetheir hind limbs as weapons duringsexual competition, so it is curious thatthey are prepared to shed them soreadily, particularly as adults cannotregrow the limb once it has been lost. Assacrificing a leg in order to survive alsoreduces the animals’ reproductivefitness, this appears to be one ofnature’s more extreme examplesof cutting off your nose to spiteyour face.10.1242/jeb.130302Emberts, Z., St. Mary, C. M. and Miller, C. W.(2016). Coreidae (Insecta: Hemiptera) limb lossand autotomy. Ann. Entomol. Soc. Am. 109,678-683.Michelle A. ReeveRoyal Veterinary Collegemireeve@rvc.ac.ukWhen symbionts overstaytheir welcomeWOLBACHIAAnimals are increasingly understood to becomplex cellular conglomerates. Whilesome parts are derived from the genomeof the host organism, the rest comprisesmicrobial symbionts. In the best of cases,these pieces of the puzzle form tightpartnerships that provide mutual benefits.However, because symbionts can also bea burden, it is sometimes useful for hoststo go it alone. But what if evictingsymbionts makes things worse? In thesecases, can hosts become addicted to theirmicrobial passengers? In a fascinatingnew report in the Proceedings of the RoyalSociety, Series B, Julien Martinez andcolleagues from the University ofCambridge, UK, describe just such anoutcome.Wolbachia bacteria are ubiquitous ininsects and infect more than half of allspecies. While best known asmanipulators of insect reproduction, thesebacteria can also play defensive roles fortheir insect hosts. In Drosophila, theyprovide protection against the highlylethal fly virus Drosophila C virus(DCV). However, flies can also becomeresistant to DCV without Wolbachia viamutations in their genomes at a singlegene called pastrel. If you can have onemode of resistance, why keep both? Thisis particularly true for Wolbachia, whosecarriage can be highly costly to flies. Andif you do carry Wolbachia, how does thisaffect the evolution of pastrel?To address these questions the teamestablished two groups of flies that wereidentical except for the presence orabsence of Wolbachia symbionts. Theythen infected flies from these treatmentswith DCV. As expected, fewer flies withthe bacterial symbiont died than thosewithout it. Some flies withoutWolbachia,however, survived, and this minorityoverwhelmingly carried mutations at thepastrel locus. By contrast, pastrelmutations in theWolbachia flies remainedat very low levels. This result indicatedthat, at least in the short term, bacterialsymbionts suppressed the evolution ofhost resistance. But what about in thelonger term?Martinez and his colleagues next rearedboth groups of DCV-infected fliesthrough nine generations. Although viralresistance increased in both fly groups,the effects on pastrel mutations weredramatically different. While pastrelmutations rapidly increased in frequencyin the flies lacking Wolbachia, becomingfixed in these populations, the ascent ofmutations in the gene was markedlyslower in flies harbouring the symbiont.More strikingly, the group estimated thatwhile DCV imposed very strong naturalselection to increase the frequency ofpastrel mutations in the no-symbiontgroup, this was almost entirely absentin flies carrying Wolbachia. Inshort, Wolbachia carriage arrested theevolution of genomic mutations for DCVresistance.So why is Wolbachia an addiction?Simply, because flies carrying costlybacterial symbionts suspend fightingDCV on their own. Thus, whenDCV is common, Wolbachia-mediatedprotection might become the only formof protection available, despite the factthat pastrel mutations could do just aswell at much lower cost. At present, theauthors are not sure if this resultextends to other defensive symbionts. Itis also unclear whether this type ofaddiction occurs with symbionts playingnon-defensive roles in other animalsor plants. More generally, is thisthe selfish route by which transientsymbionts become permanent? If so, itwould suggest that the alliance betweenanimals and microbes is not always asimple one and that evenhighly mutualistic interactions between2969OUTSIDE JEB Journal of Experimental Biology (2016) 219, 2968-2970JournalofExperimentalBiologymicrobial symbionts and hosts mayhave coercive origins.10.1242/jeb.130286Martinez, J., Cogni, R., Cao, C., Smith, S.,Illingworth, C. J. R. and Jiggins, F. M. (2016).Addicted? Reduced host resistance inpopulations with defensive symbionts. Proc. R.Soc. B 283, 20160778.Daniel E. RozenUniversity of Leidend.e.rozen@biology.leidenuniv.nlDiving beetles that handleheat better have biggerbackyardDISTRIBUTIONWhether it’s birdwatching or catchingPokémon, everybody knows that differentspecies have different geographicalranges. Some species like Canada geese,have far-flung populations spread acrossan entire continent, while others like theChristmas Island frigatebird are foundonly on a single tiny island in the middleof the ocean. While explanations for whysome species have broader ranges thanothers vary, for diving beetles it mightcome down to their ability to performunder stress.Diving beetles in the genus Deronectesare found throughout Europe; somespecies are found over areas coveringthousands of kilometres, while othersonly cover an area with a 100 km radius.Rebekah Cioffi and her colleagues atPlymouth University, UK, along withAndrés Millán from the University ofMurcia, Spain, thought each species’distribution might be linked to theirphysiological plasticity in response tothermal stress. Since the climate ofregions distributed towards the polestends to be more variable than those inmore equatorial regions and the specieswith the most widespread ranges tend tooccur in more polar areas, the researchersthought that perhaps only those speciesthat are able to rapidly adjust how theirbodies function can becomegeographically widespread.To test this idea, the researchers set out ona trans-European mission to collect fiveclosely related species of Deronectesbeetles, then brought them back to the labto test their performance under heat stress.They warmed up the beetles to 15, 20, 25,30 or 35°C, then held them at thattemperature for 24 h before placing themin the deep freeze until they could latermeasure the beetles’ metabolic stores,such as carbohydrates (glycogen andglucose) and fats. The researchers alsomeasured the beetles’ ability to mount animmune response and defined theirplasticity as the difference between thehighest and lowest values for eachmeasurement.Cioffa and colleagues found that the valuethat best explained the breadth ofdistribution of a diving beetle speciesincluded both the degree of plasticity(how much the measure of lipids,glycogen and glucose changed afterchanging temperatures) as well as howstrongly the insect’s immune systemresponded to pathogens. In particular,diving beetles that had more northerly andwidely distributed ranges also seemed tohave a greater ability to burn fat underthermal stress, which makes sensebecause fats are a more dense form ofenergy storage than carbohydratesand the fat body in insects is alsoinvolved in the production of importantimmune molecules such as antimicrobialpeptides.While the ability to survive harsherconditions closer to the poles is stillimportant for an insect species to spreadacross vast geographical ranges, theresearchers suggest that for diving beetlesat least, having physiological systems thatcan bend with changing temperatures canbe another important trait that allows themto spread far and wide.10.1242/jeb.130294Cioffi, R., Moody, A. J., Millán, A., Billington,R. A. and Bilton, D. T. (2016). Physiologicalniche and geographical range in European divingbeetles (Coleoptera: Dytiscidae). Biol. Lett. 12,20160130.Katie MarshallUniversity of British Columbiakmarshall@zoology.ubc.ca2970OUTSIDE JEB Journal of Experimental Biology (2016) 219, 2968-2970JournalofExperimentalBiology

Leaf-footed bugs choose to lose legs

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