This study analyzed the morphometric, microsatellite loci and mitochondrial control region variation of the striped weakfish from two feeding and spawning grounds in the coastal area of Buenos Aires province. The characterization of the body shape proved to be different between sites. Genetic structure analysis showed that the main source of genetic variation was within populations rather than among populations and low genetic differentiation was observed between sites. The striped weakfish inhabiting the coastal areas of Buenos Aires would exhibit two management units in agreement with other fishes studied in both areas.Fil: Sabadin, David Ezequiel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: González Castro, Mariano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Iudica, Celia Estela. Asociación de Genética Humana; ArgentinaFil: Díaz de Astarloa, Clara María. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; ArgentinaFil: Fernández Iriarte, Pedro J.. Universidad Nacional de Mar del Plata; Argentin

Díaz de Astarloa, Clara María

Fernández Iriarte, Pedro J.

González Castro, Mariano

Iudica, Celia Estela

Sabadin, David Ezequiel

Revista de biología marina y oceanografía

English

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

513Vol. 45, Nº3, 2010Revista de Biología Marina y OceanografíaRevista de Biología Marina y OceanografíaVol. 45, Nº3: 513-517, diciembre 2010Research NoteMorphometric and genetic assessment of theCynoscion guatucupa population structurefrom Buenos Aires coast, Argentine SeaEvaluación morfométrica y genética de la estructura poblacional de Cynoscionguatucupa de la costa de Buenos Aires en el Mar ArgentinoDavid E. Sabadin1, Mariano González-Castro2, Celia Iudica3,Juan M. Díaz de Astarloa2 and Pedro J. Fernández-Iriarte11Laboratorio de Genética, Departamento de Biología, Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Mardel Plata, Funes 3250, 7600 Mar del Plata, Argentina, CONICET. firiarte@mdp.edu.ar2Laboratorio de Ictiología, Departamento de Ciencias Marinas, Facultad de Ciencias Exactas y Naturales, Universidad Nacionalde Mar del Plata, Funes 3250, 7600 Mar del Plata, Argentina, CONICET3Asociación de Genética Humana, Colón 3853 (7600), Mar del Plata, ArgentinaAbstract.- This study analyzed the morphometric, microsatellite loci and mitochondrial control region variation ofthe striped weakfish from two feeding and spawning grounds in the coastal area of Buenos Aires province. Thecharacterization of the body shape proved to be different between sites. Genetic structure analysis showed that themain source of genetic variation was within populations rather than among populations and low genetic differentiationwas observed between sites. The striped weakfish inhabiting the coastal areas of Buenos Aires would exhibit twomanagement units in agreement with other fishes studied in both areas.Key words: Genetic structure, body shape, microsatellites, conservationINTRODUCTIONThe distribution pattern of genetic population structure,within and among populations is a key aspect in the fieldof conservation genetics of fish. This is crucial to identifyevolutionary and management units, which are defined asgroups of individuals exhibiting substantial reproductiveisolation or adaptive divergence or both (Crandall et al.2000). Management units, in turn, are understood as groupsof individuals among which the extent of ecological andgenetic connectivity is sufficiently low, and hence eachgroup (subpopulation or stock) must be individuallymonitored and managed (Laikre et al. 2005, Palsbøll et al.2006). The ability to identify management units or thepossibility of establishing genetic differentiation ordiscontinuity among evolutionary units in nature dependson the species life history and ecology (Waples 1998). Thefactors and main processes responsible for promotinggenetic differentiation or genetic and/or ecologicaldiscontinuities among marine populations are: historicalvicariance, limited dispersal ability (philopatry), larvalretention, local adaptation, and barriers to gene flow, suchas oceanographic fronts (salinity and temperature, amongothers) and habitat discontinuity (seabed type) (Riginos& Nachman 2001).The coastal fish species of the Argentine Sea haveshown evidence of overexploitation and signs of capturedecrease and smaller individuals, which could be affectingthe species survival (Ruarte et al. 2004). In this framework,the need to adopt monitoring measures through molecularmarkers as a key tool in management decision taking (Ward2000). However, studies conducted on genetic structureusing microsatellite loci in the Argentine Sea have beenscarce (Beheregaray & Sunnucks 2001), even if thescientific community has recognized the need to addressdiversity and genetic structure of marine fish populations(Palumbi 2003, Laikre et al. 2005). Likewise, it is worthhighlighting the fact that molecular tools are more effectivewhen combined with other approaches, includingmorphometric, oceanographic, tagging and recapture data,as well as life history variables and ecological models,among others (Ward 2000).The present study focused on the striped weakfishCynoscion guatucupa (Cuvier, 1830) (Actinopterygii,Sciaenidae) which is a wide spread demersal fish in SouthAmerica, ranging from the coast of Rio de Janeiro, Brazil(22°S), to the coasts of Chubut province, Argentina (43°S)(Cousseau & Perrotta 2004). In Argentina, it ranks second514 Sabadin et al.Cynoscion guatucupa population structurein commercial importance in the Buenos Aires coastal area(36°S to 41°S). Argentine landings of striped weakfishcome from catches from Samborombón Bay, part of theArgentine-Uruguayan Common Fishing Zone (AUCFZ)(34°S to 39°S), and from El Rincón zone to the South ofBuenos Aires province (39°S to 41°S) (Ruarte et al.2004).This study aims to provide a comparative analysisbetween morphometrics based on landmarks, microsatelliteloci and control region variation from two fishing sites inthe Buenos Aires coast, wherein the striped weakfish iscaught: Samborombón Bay and El Rincón.MATERIAL AND METHODSSTUDY AREAThe sampling comprised two spawning, feeding andnursery grounds of striped weakfish from the ArgentineSea: Samborombón Bay (36°S; 56°W) and El Rincón zone(39º05´S; 61°W) (Fig. 1). Fish were caught by trawl duringfeeding time (June and July 2008), frozen upon captureand taken immediately to the laboratory. A total of 57individuals were collected from Samborombón Bay and75 from El Rincón. Specimens were weighed, sexed, andassessed for gonad maturation stage. Muscle tissue sampleswere taken from the body and stored in plastic microtubeswith ethanol or frozen.MORPHOMETRIC ANALYSISTwenty-one morphometric variables were analyzed on theleft flank of 132 specimens, based on 10 anatomicallandmarks placed in 4 quadrilaterals («Box Truss»)obtained in line with the Truss Network protocol (Strauss& Bookstein 1982) (Fig. 2). The variables analyzed wereas follows: 1-2, 1-3, 1-4, 2-3, 2-4, 3-4, 3-5, 3-6, 4-5, 4-6,5-6, 5-7, 5-8, 6-7, 6-8, 7-6, 7-8, 7-9, 8-9, 8-10, 9-10 (Fig.2). Interlandmark distances were obtained from freshspecimens, using a digital caliper of 0.01 mm accuracy.After normalization (Lleonart et al. 2000), a PrincipalComponent Analysis (PCA) was conducted to detect shapevariations between sampling sites. PCA and DiscriminantAnalysis were computed using XLSTAT software.GENETIC ANALYSISDNA was isolated using Chelex extraction method (Estoupet al. 1996). Polymerase chain reaction (PCR) was used toamplify 2 microsatellite loci: CacMic18 and CacMic19which had yielded good results in the cross-speciesamplification between C. striatus (now C. guatucupa) andC. acoupa (Farias et al. 2006). Primers, amplifications andPCR conditions were described in Farias et al.  (2006).PCR products were genotyped by denaturingpolyacrylamide gel electrophoresis 6% (19:1 acrylamide:bisacrylamide) and visualized by silver nitrate staining.The mean number of alleles per locus, observedheterozygosity (Ho) and expected heterozygosity (He) wereestimated using GENEPOP 4.0 software (Rousset 2008).Probability tests for Hardy-Weinberg equilibrium (HWE)in each region (by locus and multilocus), and for linkagedisequilibrium between loci were performed usingGENEPOP. Whenever the genotype frequencies observedFigure 1. Map showing the study areaand sampling sites (•) of Cynoscionguatucupa at Samborombón Bay andEl Rincón / Mapa del área de estudioindicando los sitios de muestreo (•) deCynoscion guatucupa en la BahíaSamborombón y en El Rincón515Vol. 45, Nº3, 2010Revista de Biología Marina y Oceanografíadeviated significantly from HWE, MICROCHECKERanalysis (Oosterhout et al. 2004) was applied to determinethe most probable cause among various genotyping errorsand the presence of null alleles. A maximum likelihoodestimate of null allele frequency was then calculated foreach locus and population using FREENA software(Chapuis & Estoup 2007). A hierarchical analysis ofmolecular variance (AMOVA) among and between siteswas conducted as well. It was tested by 10,000permutations using the computer package ARLEQUIN3.11 (Schneider et al. 2000). The genetic differentiationbetween sites was analyzed by estimating the FST index,and the statistical significance was examined byperforming permutation tests implemented in FSTAT(Goudet 2001). Likewise the method implemented inFREENA for estimating FST in the presence of null allelewas adopted.A partial sequence of the mitochondrial control regionwas amplified using primers and the PCR conditionsdescribed by Beheregaray & Sunnucks (2001). The PCRproduct was purified and sequenced in MACROGEN(Korea). The sequences were manually aligned applyingPROSEQ 3.0 (Filatov 2002) and the differentiationbetween sites was analyzed by estimating the φST parameterusing ARLEQUIN 3.11 (Schneider et al. 2000).RESULTS AND DISCUSSIONIn Cynoscion guatucupa, eight alleles were detected forthe CacMic18 loci, whereas for CacMic19, eleven alleleswere observed. At both sampling locations, microsatelliteloci exhibited high expected heterozygosity (0.835 inSamborombón; 0.831 in El Rincón) and low observedheterozygosity (0.402 in Samborombón; 0.396 in ElRincón), with a mean of 10 alleles per locus. Highlysignificant departures from Hardy–Weinberg expectationwere recorded for each locus, such as in the multilocusanalysis conducted at each sampling location, whichyielded homozygote excess (FIS = 0.528, P < 0.001 inSamborombón; FIS = 0532, P < 0.001 in El Rincón). Onthe other hand, the MICROCHECKER analysis suggestedthe presence of null alleles in both loci with similarfrequency between them (CacMic18: 0.253 inSamborombón and 0.228 in El Rincón, and CacMic19:0.225 in Samborombón and 0.244 in El Rincón), as wellas the mean allele frequency in all populations and loci(0.238).The main explanations for such homozygote excess arenull alleles and Wahlund effect. Loci CacMic18 andCacMic19 contain null alleles which most probablyoriginate from poor cross-species PCR amplification. Thisis most likely explained by the mutations taking place inthe priming site(s) of C. guatucupa, since 24% of the allelesfailed to amplify, and being microsatellites containing 8alleles or more, most individuals should be heterozygotes.Likewise, when comparing both sampling locations,AMOVA revealed that the main variation source was withinthe fishing sites (99%) (SS=126.703; d.f. = 190; Variance= 0.667) rather than between locations (1%) (SS = 1.297;d.f. =1; Variance = 0.007) displaying no other differencesthan those expected by random (P > 0.05). Populationdifferentiation between sampling locations yielded low FSTvalues for CacMic18 (FST = 0.0001, P > 0.05) and formultilocus (FST = 0.0109, P > 0.05). With respect to locusCacMic19, the index was low but differed significantly(FST = 0.0210, P < 0.05). In the same way the estimationof FST per locus using the correction for null alleles (ENA)was lower than the uncorrected FST for CacMic18 (FST ENAFigure 2. Location of the 10 anatomicallandmarks with the corresponding 'Box Truss'of Cynoscion guatucupa / Localización de los10 'landmarks' anatómicos de Cynoscionguatucupa con su correspondiente 'Box Truss'516 Sabadin et al.Cynoscion guatucupa population structure= -0.0002), for CacMic19 (FST ENA = 0.0128) as well asfor multilocus (FST ENA = 0.0069). In addition, thesequence of 365 bp obtained from the control region for47 individuals from Samborombón Bay (n = 22) and fromEl Rincón (n = 25), showed a low genetic differentiationindex that not differed significantly between sampling sites(φST = - 0.0172, P > 0.05). This pattern of genetic structurecould be attributed to high recent and historical gene flow.The low genetic differentiation values can be explainedby panmixia between populations or by different lineageswhich have recently diverged and so changes cannot bedetected (Waples 1998, Palumbi 2003). Nonetheless,conclusions should be drawn with caution in this case, asthis study only explored two microsatellite loci.The characterization of the striped weakfish body shapeindicated a clear differentiation among individuals fromboth sampling sites (Fig. 3). The three first axes of thePCA accounted 60% of the total variance in the data. Thosefrom Samborombón Bay were mainly located in the firstand fourth quadrant, while those from El Rincón werefound in the second and third one (Fig. 3). The individualsfrom Samborombón Bay displayed higher values than themean for 3-4, 3-6, 4-5, 5-6, 5-8, 6-7, and 9-10 variables,corresponding to 'Box Truss' 2 and 3 and, to a lesser extent,to 'Box Truss' 4. The individuals from El Rincón, in turn,displayed lower values than the mean for 8-10 and 7-9variables and higher for 1-2, 1-4, and 2-4, correspondingto 'Box Truss' 4 and, to a lesser extent, to 'Box Truss' 1.The Discriminant Analysis of the morphometric variationusing the normalized data yielded highly significantdifferences between both sampling locations (Wilks’lambda = 0.238, F (21, 110) = 16.76, P < 0.001). This indicatesthat individuals from Samborombón Bay exhibited higherand more robust bodies, while those from El Rincónfeatured greater length and lesser height of the caudal fin.These results contribute to the differentiation ofindividuals from the northern coast of Buenos Airesprovince with respect to those from the southern coast ofEl Rincón (Díaz de Astarloa & Bolasina 1992, Volpedo &Fernández-Cirelli 2006) and constitute a new indicator ofthe presence of more than one management unit in thisdistribution area. The differentiation in management unitsbetween the individuals of C. guatucupa fromSamborombón Bay and El Rincón zone, in agreement withother fishes studied in both areas (Braicovich & Timi 2008,Timi et al. 2009), could be associated with the fact thatthe waters from both fishing sites display notoriousoceanographic differences (Acha et al. 2004). Theindividuals from Samborombón Bay and El Rincón fishingsites showed low genetic differentiation (microsatellitesand control region). However, the different morphologicalpatterns noticed in the sampling locations would allowidentifying local differentiation processes, therebysuggesting the existence of at least two management unitsfor the striped weakfish in the Argentine Sea.ACKNOWLEDGMENTSThe authors gratefully thank Dr. Izeni P. Farias for kindlyproviding the primers of Cynoscion acoupa. We wish tothank two anonymous reviewers for valuable suggestions.This work was supported by the following grants: PIP 6357Figure 3. Principal Component (PC1 vs. PC2) basedon landmarks at Cynoscion guatucupa fromSamborombón Bay and El Rincón / ComponentesPrincipales (CP1 vs. CP2) basado en los landmarks deCynoscion guatucupa en Bahía Samborombón y El Rincón517Vol. 45, Nº3, 2010Revista de Biología Marina y Oceanografía(CONICET), PIP 2504 (CONICET) and 15/E398(UNMdP) awarded to P.F.I., M.G.C. and J.M.D.A. aremembers of the Scientific Researcher Program ofCONICET (Argentina).LITERATURE CITEDAcha EM, HM Mianzan, RA Guerrero, M Favero & J Bava.2004. Marine fronts at the continental shelves of australSouth America physical and ecological processes. Journalof Marine System 44: 83-105.Beheregaray LB & P Sunnucks. 2001. Fine-scale geneticstructure, estuarine colonization and incipient speciationin the marine silverside fish Odontesthes argentinensis.Molecular Ecology 10: 2849-2866.Braicovich PE & JT Timi. 2008. 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Genetic in fisheries management.Hydrobiologia 420: 191-201.Recibido el 11 de febrero de 2010 y aceptado el 24 de junio de 2010

Evaluación morfométrica y genética de la estructura poblacional de Cynoscion
guatucupa de la costa de Buenos Aires en el Mar Argentino

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Evaluación morfométrica y genética de la estructura poblacional de Cynoscion guatucupa de la costa de Buenos Aires en el Mar Argentino

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