Integrated morphometrics reveals conservatism in the cryptic yellowstripe scad (Perciformes: Carangidae) lineages from the Tropical Western Pacific

Abstract

Studies on the yellowstripe scad Selaroides leptolepis (Cuvier and Valenciennes, 1833), a commercially important commodity in Southeast Asia, emphasized the strengthening of management programs due to overexploitation of populations as reported from numerous fishing grounds. S. leptolepis from the Tropical Western Pacific (TWP) was previously identified to compose two allopatric mtDNA lineages – Asian and Australian, thus emerging the need to determine morphological distinctness to facilitate the management efforts. This study assessed the morphological variation of the two genetic lineages using integrated morphometrics. One hundred forty-three S. leptolepis individuals collected throughout TWP were subjected to (1) traditional lineal morphometrics with meristics, (2) landmark-based truss, and (3) geometric morphometrics. Principal component analysis (PCA) revealed highly overlapped ordination diagrams on all three techniques, which indicated minimal differentiation in the morphometries. Discriminant function analysis (DFA) showed satisfactory accuracy (92.2%–94.9%) in identifying Asian individuals, yet poor accuracy (47.6%–50.0%) towards determining Australian individuals. Cluster Analysis (CA) suggested K = 1 morphological group based on geometry while K = 2 groups according to the distance-based lineal and truss morphometrics. However, further validation indicated that cluster memberships were mixed and poorly reflected the a priori groupings. Herein, combinative results indicated the existence of a single morphological unit in S. leptolepis, which supported that such groups are genetically distinct yet morphologically indistinguishable cryptic lineages. These findings serve as essential groundwork for the formulation of management strategies for the species given their economic relevance.