Determination of the Presence of Auxis rochei and Auxis thazard (Actinopteri: Scombridae) Species Distributed in Turkish Seas Using Phylogenetic and Morphometric Methods

Project no. 32252 · Status: Kapanmış (Yayın bekleniyor) · 2024

Summary

<p><em>Auxis&nbsp;rochei</em>&nbsp;and&nbsp;<em>Auxis&nbsp;thazard</em>&nbsp;are&nbsp;two&nbsp;pelagic&nbsp;species&nbsp;of&nbsp;the&nbsp;family&nbsp;Scombridae&nbsp;that&nbsp;may&nbsp;be&nbsp;misidentified&nbsp;due&nbsp;to&nbsp;their&nbsp;close&nbsp;morphological&nbsp;resemblance.&nbsp;The&nbsp;present&nbsp;study&nbsp;aimed&nbsp;to&nbsp;verify&nbsp;the&nbsp;species&nbsp;identity&nbsp;of&nbsp;Auxis&nbsp;specimens&nbsp;collected&nbsp;from&nbsp;Turkish&nbsp;seas&nbsp;using&nbsp;an&nbsp;integrated&nbsp;approach&nbsp;combining&nbsp;geometric&nbsp;morphometrics&nbsp;and&nbsp;molecular&nbsp;analyses.&nbsp;In&nbsp;2024-2025,&nbsp;a&nbsp;total&nbsp;of&nbsp;90&nbsp;specimens&nbsp;were&nbsp;obtained,&nbsp;including&nbsp;44&nbsp;individuals&nbsp;from&nbsp;the&nbsp;Aegean&nbsp;Sea&nbsp;and&nbsp;46&nbsp;individuals&nbsp;from&nbsp;the&nbsp;Mediterranean&nbsp;Sea.&nbsp;Geometric&nbsp;morphometric&nbsp;analyses&nbsp;were&nbsp;performed&nbsp;on&nbsp;74&nbsp;individuals&nbsp;deemed&nbsp;suitable&nbsp;for&nbsp;morphological&nbsp;analyses,&nbsp;using&nbsp;12&nbsp;anatomical&nbsp;landmarks.&nbsp;Generalized&nbsp;Procrustes&nbsp;Analysis&nbsp;(GPA)&nbsp;and&nbsp;Principal&nbsp;Component&nbsp;Analysis&nbsp;(PCA)&nbsp;were&nbsp;applied,&nbsp;and&nbsp;group-level&nbsp;shape&nbsp;differences&nbsp;were&nbsp;statistically&nbsp;tested&nbsp;using&nbsp;Procrustes&nbsp;ANOVA,&nbsp;Canonical&nbsp;Variate&nbsp;Analysis&nbsp;(CVA),&nbsp;and&nbsp;Discriminant&nbsp;Function&nbsp;Analysis&nbsp;(DFA).&nbsp;&nbsp;For&nbsp;molecular&nbsp;analyses,&nbsp;DNA&nbsp;was&nbsp;extracted&nbsp;from&nbsp;45&nbsp;specimens,&nbsp;and&nbsp;the&nbsp;mitochondrial&nbsp;cytochrome&nbsp;c&nbsp;oxidase&nbsp;subunit&nbsp;I&nbsp;(COI)&nbsp;gene&nbsp;region&nbsp;was&nbsp;successfully&nbsp;amplified&nbsp;and&nbsp;sequenced&nbsp;in&nbsp;30&nbsp;individuals.&nbsp;Geometric&nbsp;morphometric&nbsp;analyses&nbsp;revealed&nbsp;statistically&nbsp;significant&nbsp;body&nbsp;shape&nbsp;differences&nbsp;between&nbsp;the&nbsp;Aegean&nbsp;Sea&nbsp;and&nbsp;Mediterranean&nbsp;Sea&nbsp;populations&nbsp;even&nbsp;after&nbsp;controlling&nbsp;for&nbsp;size&nbsp;effects&nbsp;(F&nbsp;=&nbsp;2.76,&nbsp;R²&nbsp;=&nbsp;0.036,&nbsp;p&nbsp;=&nbsp;0.024).&nbsp;Leave-one-out&nbsp;cross-validation&nbsp;classification&nbsp;accuracy&nbsp;was&nbsp;74.3%,&nbsp;and&nbsp;Mediterranean&nbsp;specimens&nbsp;were&nbsp;characterised&nbsp;by&nbsp;a&nbsp;deeper&nbsp;anterior&nbsp;body&nbsp;profile&nbsp;and&nbsp;a&nbsp;broader&nbsp;caudal&nbsp;peduncle&nbsp;compared&nbsp;to&nbsp;Aegean&nbsp;Sea&nbsp;specimens.&nbsp;However,&nbsp;phylogenetic&nbsp;analyses&nbsp;based&nbsp;on&nbsp;COI&nbsp;sequences&nbsp;demonstrated&nbsp;that&nbsp;all&nbsp;examined&nbsp;specimens&nbsp;clustered&nbsp;within&nbsp;the&nbsp;same&nbsp;clade&nbsp;together&nbsp;with&nbsp;reference&nbsp;sequences&nbsp;of&nbsp;<em>Auxis&nbsp;rochei</em>.&nbsp;In&nbsp;contrast,&nbsp;reference&nbsp;sequences&nbsp;of&nbsp;<em>A.&nbsp;thazard</em>&nbsp;formed&nbsp;a&nbsp;distinct&nbsp;clade,&nbsp;and&nbsp;the&nbsp;separation&nbsp;between&nbsp;the&nbsp;two&nbsp;species&nbsp;was&nbsp;strongly&nbsp;supported&nbsp;by&nbsp;high&nbsp;bootstrap&nbsp;values.&nbsp;None&nbsp;of&nbsp;the&nbsp;analyzed&nbsp;specimens&nbsp;were&nbsp;grouped&nbsp;within&nbsp;the&nbsp;<em>A.&nbsp;thazard</em>&nbsp;clade,&nbsp;indicating&nbsp;that&nbsp;all&nbsp;sampled&nbsp;individuals&nbsp;belonged&nbsp;to&nbsp;<em>A.&nbsp;rochei</em>.&nbsp;These&nbsp;findings&nbsp;demonstrate&nbsp;that&nbsp;the&nbsp;morphological&nbsp;differences&nbsp;observed&nbsp;between&nbsp;the&nbsp;Aegean&nbsp;Sea&nbsp;and&nbsp;Mediterranean&nbsp;populations&nbsp;reflect&nbsp;intraspecific&nbsp;phenotypic&nbsp;variation&nbsp;within&nbsp;<em>A.&nbsp;rochei</em>&nbsp;rather&nbsp;than&nbsp;species-level&nbsp;differentiation,&nbsp;and&nbsp;further&nbsp;highlight&nbsp;the&nbsp;importance&nbsp;of&nbsp;molecular&nbsp;validation&nbsp;for&nbsp;reliable&nbsp;species&nbsp;identification.&nbsp;This&nbsp;study&nbsp;provides&nbsp;valuable&nbsp;information&nbsp;on&nbsp;the&nbsp;taxonomy&nbsp;of&nbsp;<em>Auxis</em>&nbsp;species&nbsp;in&nbsp;Turkish&nbsp;seas&nbsp;and&nbsp;suggests&nbsp;that&nbsp;previously&nbsp;reported&nbsp;records&nbsp;of&nbsp;<em>A.&nbsp;thazard</em>&nbsp;in&nbsp;the&nbsp;region&nbsp;should&nbsp;be&nbsp;re-evaluated&nbsp;using&nbsp;molecular&nbsp;approaches.</p>

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