Adelino V. M. Canário

AP Scott

B Borg

JC Wingfield

K Hirschenhauser

Luis A. Carneiro

P Martin

RF Oliveira

Rui F. Oliveira

WJ Rowland

Nature

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No hormonal response in tied fights

Oliveira, Rui Filipe

Carneiro, Luís Alberto

Canário, Adelino V. M.

Repositório do ISPA

Vol 437|8 September 2005207No hormonal response in tied fights Fish androgens may start to surge only when there seems to be a good chance of winning a contest.Androgens are the principal sex steroids con-trolling reproduction and aggression in malefish1, but their production can also be affectedby social interactions2,3. Here we show thatandrogen concentrations are not significantlyincreased in cichlid fish (Oreochromismossambicus) that are fighting their ownimage in a mirror, despite their aggressivebehaviour towards the virtual intruder. Ourresults indicate that the hormonal responsenormally triggered in male contests is notinduced under these circumstances by the actof fighting itself, and that it may thereforedepend on some indicator of relative fightingability that cannot be delivered by a mirror-image challenger.Fish do not recognize their own image in amirror and so attack it as though it were anintruder4. However, there are no pointers (suchas differences in rank, strength, injury orfatigue) that can be used to assess the outcomeof the attack (winning versus losing) for a fishin this situation. To test whether informationon interaction outcome is necessary to triggeran androgen response in fighting fish, we com-pared androgen concentrations in the urine offish after mirror-mediated challenge with thosein urine from non-fighting controls. Male cichlids of comparable size and age,raised in similar conditions, were kept in socialisolation for seven days before the experimentto minimize inter-individual variation inbehavioural and androgen responses that arisefrom differences in social status5. On the day ofthe experiment, the fish were divided into twogroups: one was presented with a mirror at oneend of the tank (experimental group; n17);the other had a sheet of transparent glassinstead to control for the presence of a novelobject in the aquarium (control group; n14).We recorded the fighting behaviour of the fish(aggressive displays and attacks) for 20 minafter the first interaction with the mirror orglass by using a focal continuous recordingmethod6. The principal fish androgens1, testos-terone and 11-keto-testosterone, were mea-sured by specific radioimmunoassay of urinecollected 60 min before the test (baseline value)and 30 min, 2 h and 6 h after the end of the test.Individuals reacted very aggressively totheir own image in the mirror, whereas thepresence of non-reflective glass in the tank didnot provoke a combative response in fish fromthe control group. During the course of theattacks, the aggression of subjects in theexperimental group escalated towards theirmirror images as they apparently tried toresolve the ‘contest’ (Fig. 1a). However, despite the marked degree ofaggressive behaviour, no significant increase inurine androgens was detected in the experi-mental relative to the control group (Fig. 1b, c).This contrasts with the increased productionof androgens in O. mossambicus males inresponse to territorial intrusions by conspe-cific males7, and with the androgen increase inmale spectators that are not even directly par-ticipating in a fight8. Although there is a reduc-tion in androgen synthesis in fish that losefights and become subordinates5, this cannotaccount for the drop in androgens in theexperimental group, which is similar to that inthe non-fighting control group and is in therange expected for the time of day (morning)at which the measurements were made. We conclude that information on the likelyoutcome of a contest is required before theandrogen response is triggered in a combatant,and that escalation of the fight occurs inde-pendently of circulating androgen levels. Thismay be an adaptive mechanism that allowsindividuals to mount an androgen response forthe purpose of controlling their social statusafter they have assessed the relative fightingability of their challenger. Rui F. Oliveira*, Luis A. Carneiro*,Adelino V. M. Canário†*Unidade de Investigação em Eco-Etologia,Instituto Superior de Psicologia Aplicada, BRIEF COMMUNICATIONS0 5 10Time (min)2015 2548120–2–4–6NS NS NS–80.5 2.0Time after exposure to stimuli (h)6.0NS NS NS–2–4–60–8n=16n=14n=16n=14n=16n=11n=16n=11n=17 n=10n=17n=100.5 2.0Time after exposure to stimuli (h)6.0abcTestosterone variation(ng ml–1)11-keto-testosteronevariation (ng ml–1)016Mean number ofantagonistic actsFigure 1 | Mirror-elicited aggression in cichlidmale fish fails to trigger an androgen response.a, Escalation in antagonism by fish towards theirown image in a mirror, as measured by variationin the frequency of aggressive displays andattacks on the mirror during the period of thetrial. Red circles, controls (clear glass in the tankinstead of a mirror), n14; blue triangles,experimental group, n17. The differencebetween the two regression lines was tested with analysis of covariance using BIOM software (copyright F. James Rohlf, 1984); slopes: F29.97, P0.001; means: F 110.26,P0.001. b, c, Variation in fishes’ total urinaryconcentrations (freesulphateglucuronide) oftestosterone (b) and 11-keto-testosterone (c) afterexposure to a mirror (blue bars) or to clear glass(red bars) for 20 min (calculated as the differencein concentration before and after stimulation;error bars, s.e.m.). Urine was collected in anEppendorf tube by applying gentle pressure in theventro-posterior flank of the fish. Sample sizesdiffer because urine was not obtained from allindividuals at all sampling points. Sampleprocessing and radioimmunoassay were done as described5,9,10. NS, not significant in Mann–Whitney tests.Duel action: a cichlid attacks its reflection.8.9 brief comms MH  1/9/05  5:02 PM  Page 207Nature Publishing Group© 2005BRIEF COMMUNICATIONS NATURE|Vol 437|8 September 20052081149-041 Lisboa, Portugale-mail: ruiol@ispa.pt†CCMar, Universidade do Algarve, Campus deGambelas, 8005-139 Faro, Portugal1. Borg, B. Comp. Biochem. Physiol. C 109, 219–245 (1994).2. Oliveira, R. F. Adv. Study Behav. 34, 165–239 (2004).3. Wingfield, J. C., Hegner, R. E., Dufty, A. M. & Ball, G. F. Am. Nat. 136, 829–846 (1990).4. Rowland, W. J. Environ. Biol. Fish. 56, 285–305 (1999).5. Oliveira, R. F., Almada, V. C. & Canário, A. V. M. Horm.Behav. 30, 2–12 (1996).6. Martin, P. & Bateson, P. Measuring Behaviour: An IntroductoryGuide (Cambridge Univ. Press, Cambridge, 1993).7. Hirschenhauser, K., Taborsky, M., Oliveira, T., Canário, A. V. M. & Oliveira, R. F. Anim. Behav. 68, 741–750 (2004).8. Oliveira, R. F., Lopes, M., Carneiro, L. A. & Canário, A. V. M.Nature 409, 475 (2001).9. Scott, A. P. & Sumpter, J. P. Gen. Comp. Endocrinol. 73,46–58 (1988). 10. Scott, A. P., Mackenzie, D. S. & Stacey, N. E. Gen. Comp.Endocrinol. 56, 349–359 (1984).Competing financial interests: declared nonedoi:10.1038/437207a1. Couder, Y., Fort, E., Boudaoud, A. & Gautier, C. H. Phys. Rev.Lett. 94, 177801 (2005).2. Fauve, S. & Thual, O. Phys. Rev. Lett. 64, 282–284 (1990).3. Aranson, I. S., Gorshkov, K. A., Lomov, A. S. & Rabinovich, M. I. Physica D 43, 435–453 (1990).4. Lioubashevski, O., Arbell, H. & Fineberg, J. Phys. Rev. Lett.76, 3959–3962 (1996).5. Umbanhowar, P. B., Melo, F. & Swinney, H. L. Nature 382,793–796 (1996).6. Stegeman, G. I. & Segev, M. Science 286, 1518–1523 (1999).7. Moskalenko, A. S., Liehr, A. W. & Purwins, H. G. Eur. Phys.Lett. 63, 361–367 (2003).8. Liehr, A. W., Moskalenko, A. S., Astrov, Y. A., Bode, M. &Purwins, H. G. Eur. Phys. J. B 37, 199–204 (2004).9. Boudaoud, A., Couder, Y. & Ben Amar, M. Eur. Phys. J. B 9,159–165 (1999).10. Boudaoud, A., Couder, Y. & Ben Amar, M. Phys. Rev. Lett. 82,3847–3851 (1999).Supplementary information accompanies thiscommunication on Nature’s website.Competing financial interests: declared nonedoi:10.1038/437208aBRIEF COMMUNICATIONS ARISING online➧ www.nature.com/bca see Nature contents.Small drops can bounce indefinitely on a bathof the same liquid if the container is oscillatedvertically at a sufficiently high acceleration1.Here we show that bouncing droplets can bemade to ‘walk’ at constant horizontal velocityon the liquid surface by increasing this acceler-ation. This transition yields a new type of local-ized state2–5 with particle–wave duality: surfacecapillary waves emanate from a bouncing drop,which self-propels by interaction with its ownwave and becomes a walker. When two walkerscome close, they interact through their wavesand this ‘collision’ may cause the two walkers toorbit around each other6-8. The bouncer transition to walking is contin-uous and occurs when the vertical accelerationof the bath, m, reaches a critical threshold, mc.Below mc, the drops bounce with no horizon-tal motion. Above mc, bouncing drops acquirea rectilinear motion along the surface of thebath (Fig. 1a–c). Their velocity Vw is constant(0–20 mm s1) and increases with m. Why do the drops start walking? This phe-nomenon occurs below, but near, the onset ofthe Faraday instability, a point at which thesurface becomes spontaneously wavy. In thisregime, the vertical motion of a drop becomessubharmonic, with a period that is double thatof the forcing. As a result, it emits a dampedFaraday wave. The drop undergoes successiveidentical parabolic jumps that are locked withits wave. Each jump brings the drop into colli-sion with the side of the central bulge of the wave generated by the previous collision(Fig. 1a). This collision with an inclined surfacegenerates a non-zero horizontal impulse, whichcan be translated as an equation for the drop’shorizontal motion, averaged over a period/0 of the subharmonic vertical motionm d2x/dt2a sin{(k/0) dx/dt}b dx/dt (1)where m is the drop’s mass, a is about 106 N, kis the wavenumber, and b is about 106 N m1 s.The left-hand side of equation (1) representsthe inertia of the drop; the first term on theright-hand side accounts for the effective forcedue to the inclined surface, and the second forviscous damping during the collision. EquationDYNAMICAL PHENOMENAWalking and orbiting droplets(1) predicts the observed continuous transi-tion of the droplet from stationary to walkingwhen ab0/(k).When walkers coexist in a cell, theyinevitably collide. These ‘collisions’ do notinvolve any contact between the drops but onlya deflection of their horizontal trajectories,when the wave generated by a drop affects thehorizontal velocity of the other one. The mainparameter characterizing this collision is dc ,the minimal distance of approach of the twodrops; depending on the value of dc, the walk-ers either attract or repel each other. Attractionleads to a twin-star-like orbiting motion of thedrops (Fig. 1d, and see movie in supplementaryinformation). The diameters of the orbits takediscrete values dnorb, which self-adapt to theforcing frequency9,10. The orbital diameters areslightly smaller than an integer multiple of theFaraday wavelength (	F), or dnorb(n)	Fwhen the drops bounce in phase. They arednorb(n1/2)	F when the drops bouncein antiphase; the offset, 0.20.02, is suchthat when a drop collides with the surface, itfalls on the inward slope of the wave emitted bythe other. This provides the centripetal forceneeded for the orbital motion. For other valuesof dc , each drop falls on the outward slope ofthe wave of the other, which causes a repulsion. We have shown that walkers can behave asbilliard balls, undergo scattering collisions orform circular orbits, and can even display com-plex three-body motion (results not shown).The variety of these phenomena can beexplained by interaction through waves and bygeneralizing equation (1) to two or more drops(the resulting equations yield the same quan-tification of orbits and numerical trajectories,which are very similar to the experimental col-lisions; S. P. et al., manuscript in preparation). Inthis system, real particles experience the samenon-local interaction as nonlinear waves.Y. Couder*, S. Protière*, E. Fort†, A. Boudaoud‡*Matières et Systèmes Complexes, and †Matériauxet Phénomènes Quantiques, Université Paris 7Denis Diderot, 75005 Paris, France ‡Laboratoire de Physique Statistique,24 rue Lhomond, 75231 Paris, Francee-mail: boudaoud@lps.ens.frFigure 1 | Behaviour of silicon oil droplets on a bathof silicon oil when it is oscillated vertically.Experimental parameters: oil viscosity,20103 Pa s; forcing frequency, 0/280 Hz,diameter of droplets D0.65 mm; forcingacceleration, m/g3.9 (where g is the accelerationdue to gravity). a–c, Photographs showing themotion of a single drop in interaction with its ownlocalized Faraday wave on the liquid surface. Thedrop’s motion is composed of a series of identicalparabolic jumps, each jump bringing the drop intocollision with the forward side of the central bulgeof the wave generated by the previous collision.d, Photograph of two orbiting drops andassociated waves. The horizontal motion is in a twin-star-like orbit of diameter dn5.8 mm. (For movies, see supplementary information.)8.9 brief comms MH  1/9/05  5:02 PM  Page 208Nature Publishing Group© 2005

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No hormonal response in tied fights

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