Ecomorphological trends and phylogenetic inertia of otolith sagittae in Nototheniidae

Abstract

A quantitative ecomorphological study was carried out on the sagitta otoliths of Antarctic and Subantarctic nototheniids, a particularly interesting family due to its fast adaptive radiation into different life strategies. We analyzed the otolith shape and size of 18 nototheniids to test the relationship between phylogeny, otolith characters and trophic niche. Relative size (area, length, width, perimeter and weight) and shape (biometric warp analysis based on homologous and pseudo-homologous landmarks) measurements were compared with phylogenic, habitat dwelling and food composition analyses. The results of the multivariate analysis of these factors indicate that there is a weak relationship between otolith shape of nototheniids and phylogeny; however, there is a clear correspondence between relative otolith size and shape and their trophic niche. The most benthic feeders of the family had the largest sagittae in relation to body size, and pelagic species had smaller and rounder shaped sagittae than benthic species. Consequently, in ecomorphological studies, it is useful to analyze the size and shape of sagittae. The discoidal shape of pelagic species, such as Pleuragrama antracticum, can be considered as a paedomorphic characteristic, converging to the juvenile sagittae of many species, which exhibit round sagittae that become elongated as they grow.