Form-function of the sulcus acusticus of the sagittae otolith in seven Sciaenidae (Acanthuriformes) species using geometric morphometrics (Southwestern Atlantic)

The morphology of the otoliths determines the function they perform and it is influenced by genetic and environmental factors. Know those relationships is necessary to understand the role of hearing in fish. The objectives of this work were: to explore the shape of the sulcus of the sagitta otolith in seven species of Sciaenidae, in relation to sound production; and analyze if the shape and size of the sulcus can be used as a phylogenetic character. For this, geometric morphometry analysis was carried out using landmarks data. It was found that there is an influence of the size on the shape of the sulcus, and significant differences were found between the shapes of the sulcus (PERMANOVA). Three general shapes of the sulcus were identified (Principal Component Analysis, Canonical Variate Analysis and clustering): 1) in species that produce sounds at dominant frequencies below 350 Hz, the deformation of the sulcus showed a tendency towards circularity of the ostium; 2) those that produce sounds at frequencies greater than 350 Hz, the ostium presented a flattened ovoid shape and the cauda increased its length; 3) the species that do not produce sounds did not present modifications in relation to the form of consensus. Despite finding in the phylogeny sister species that presented similar sulcus shapes, the results did not confirm that this can be used as a phylogenetic character. It is discusses whether the combined effects of phylogenetic legacy and natural functional selection have led to convergent evolution for the sulcus form. The differences presented by the sulcus of species that occupy the same clade, could indicate that there is a displacement of characters. The sagitta otolith and the sensory macula associated with the sulcus acusticus are highly plastic structures that are subject to strong evolutionary pressure in relation to environmental and behavioral factors, giving rise to a great variability of shapes that can be associated with a specific character. The variation in the shape of the sulcus would allow, the analyzed species, to coexist in the same coastal soundscapes, without losing their particular hearing needs, even overlapping their spatial and temporal distribution areas. This article is protected by copyright. All rights reserved.