Otolith fluctuating asymmetry: a misconception of its biological relevance?

CentroOceanogra´fico de Gijo´n, Avda. Pri´ncipe de Asturias, 70 Bis, 33212 Gijo´n, Asturias, Spain*Corresponding author: tel: +34 971610829; e-mail: cdiaz@imedea.uib-csic.esDi´az-Gil,C.,Palmer,M.,Catala´n,I.A.,Alo´s,J.,Fuiman,L.A.,Garci´a,E.,Gil,Mari´adelMar,Grau,A.,Kang,A.,Maneja,R.H.,Mohan,J.A., Morro, B., Schaffler, J. J., Buttay, L., Riera-Batle,I., Tolosa,B.,and Morales-Nin, B. Otolith fluctuating asymmetry: a misconceptionof its biological relevance? – ICES Journal of Marine Science, doi: 10.1093/icesjms/fsv067.Received12 November 2014; revised 23 March 2015; accepted 28 March2015.For decades, disruption of the bilateral symmetry of body structures has been related to underperformance and, hence, to fitness. In fish, thisconceptcoupledwiththeclaimedevidenceforincreasedfluctuatingasymmetry(FA)ofpairsofhardstructures,suchasotolithsunderconditionsofstress,hasledtotheuseofotolithFA(OFA)asaproxyforindividualfitnessandpopulationsuccess.InterpretingthosesignificantdifferencesinOFAinrelationtostress-inducingenvironmentsandusingthemtoidentifysuboptimalconditionsforsurvivalisespeciallyappealinginthecontextof,forexample,assessingclimatechangeusinghistoricalotolithcollections.DespiteseveralworksthatgiveevidencetosupporttheusefulnessofOFAapproach,wereportonanumberofunpublishedandpublisheddatasetsfromawiderangeofboth,wildpopulationsandexperimentaldesignsthatshownocorrelationbetweenOFAandanyoftheusualindicatorsoffitnessorbetweenOFAandexpectedstressgradients.Ourresultssuggestthattheremaybeastrongbiasinthepublishedliteraturetowardspositiverelationships,despitetheenormousimportanceofnegativeresultsforunderstanding the significance of OFA. These results might shed light on the interpretabilityof OFAin both laboratory and field studies.Keywords: fitness, fluctuating asymmetry,negative results, otolith.