Systematic implications of brain morphology in potamotrygonidae (Chondrichthyes: Myliobatiformes)

Abstract

The gross brain morphology, brain proportions, and position of cranial nerves in all four genera (Potamotrygon, Plesiotrygon, Paratrygon, and Heliotrygon) and 11 of the species of the Neotropical stingray family Potamotrygonidae were studied to provide new characters that may have a bearing on internal potamotrygonid systematics. The brain was also studied in four other stingray (Myliobatiformes) genera (Hexatrygon, Taeniura, Dasyatis, and Gymnura) to provide a more inclusive phylogenetic context for the interpretation of features of the brain in potamotrygonids. Our results indicate, based on neuroanatomical characters, that the genera Paratrygon and Heliotrygon are sister groups, as are the genera Potamotrygon and Plesiotrygon, agreeing with previous morphological and molecular phylogenetic studies. Both groups of genera share distinct conditions of the olfactory tracts, telencephalon and its central nuclei, hypophysis and infundibulum, morphology and orientation of the metencephalic corpus cerebelli, orientation of the glossopharyngeal nerve, and overall encephalic proportions. The corpus cerebelli of Paratrygon and Heliotrygon is interpreted as being more similar to the general batoid condition and, given their phylogenetic position highly nested within stingrays, is considered secondarily derived, not plesiomorphically retained. Our observations of the corpus cerebelli of stingrays, including Hexatrygon, corroborate that the general stingray pattern previously advanced by Northcutt is derived among batoids. The morphology of the brain is shown to be a useful source of phylogenetically informative characters at lower hierarchical levels, such as between genera and species, and thus, has significant potential in phylogenetic studies of elasmobranchs.

Neuroanatomy of Two Species of Genus Myliobatis (Chondrichthyes: Myliobatoidea)

“…In different elasmobranch species, it has been described that the cerebellum is formed by three lobes, and the anterior lobe is the largest (Northcutt, 1989;Puzdrowski & Leonard, 1992;Walker & Sherman;Fontanelle & Carvalho). However, in the two Myliobatis species in this study, four lobes were observed: one anterior, one medium and two posterior -the anterior being slightly smaller than the posterior one.…”

Chromosomal characterization of Amazonian freshwater stingrays with evidence for new karyomorphs and XX/XY sex chromosomes

“…The increasing interest in the evolution of Potamotrygoninae has emphasized the need for a proper taxonomic classification and a well-supported phylogeny to better address the issues related to the evolutionary history of the group and the diversification of the stingrays in freshwater environments (Carvalho et al , 2003; Lovejoy et al , 2006; Toffoli et al , 2008; Rosa et al , 2010; Carvalho and Lovejoy, 2011; Cruz et al , 2012; Fontenelle and Carvalho, 2016; Carvalho et al , 2016b).…”

Brain morphology of Gymnura lessae and Gymnura marmorata (Chondrichthyes: Gymnuridae) and its implications for batoid brain evolution

“…marmorata is very similar to the brains of other known Gymnura species, including G . micrura (Fontanelle & Carvalho, 2015), G . altavela (Hoffman, 1999), and G .…”

“…Brain anatomy variation has been described in some batoid groups, including Dasyatis americana (Northcutt, 1989), Urobatis jamaicensis (Walker & Sherman, 2001), Mobula (Ari, 2011), potamotrygonids (Fontanelle & Carvalho, 2015), Diplobatis ommata (Montes, López, & González, 2014), and Myliobatis (Montes‐Domínguez, Ayala‐Pérez, Castillo‐Rivera, González‐Isáis, & Reynoso, 2020). However, studies on gymnurid brain anatomy are scarce and do not include illustrations of the brain without a cerebellum (C) or a description of the auricles.…”

“…micrura (now G . lessae ) in the dorsal and ventral views without exposing details below the C. Finally, Fontanelle and Carvalho (2015) described the brain morphology of four genera ( Paratrygon , Heliotrygon , Potamotrygon , and Plesiotrygon ) of the family Potamotrygonidae. They also described the brains of four myliobatoid species, including G .…”