Morphological diversity of the Cynoscion group (Perciformes: Sciaenidae) in the Gulf of Guayaquil region, Ecuador: A comparative approach

Synopsis

We assess morphological diversity of species of the Cynoscion group in the Gulf of Guayaquil (GOG) using traditional morphometric methods. Five species from the GOG assemblage (C. albus, C. analis, C. phoxocephalus, C. squamipinnis, and Isopisthus remifer) are compared to four species from a relatively well-studied assemblage in the western Atlantic (C. arenarius, C. nebulosus, C. nothus, and C. regalis). The two regional species assemblages broadly overlap in morphology, but sympatric species segregate relatively well within each assemblage. The GOG species segregate primarily along the major axis of shape variation in the study, which is associated with variation in the anal, second dorsal, and caudal fins. The western Atlantic species segregate primarily along the second major axis of shape variation, which is most strongly associated with variation in gill raker length, and less strongly with pectoral fin length, eye diameter, and length of the third dorsal spine. Patterns of morphological divergence among the western Atlantic species support the hypothesis that morphological divergence is associated with ecological divergence. Comparisons across assemblages indicate that morphological divergence among species in the GOG is substantial. Consequently, Cynoscion species in the GOG may be highly divergent in ecological habits, which would have important management implications, but further ecological research is needed. This study provides a first glimpse into the major patterns of morphological diversification in the Cynoscion group.