Electric fishes of the genus Sternarchorhynchus (Teleostei, Ostariophysi, Gymnotiformes); phylogenetic and revisionary studies

Abstract

Analysis of 88 characters of external and internal body systems yielded a phylogenetic reconstruction of the Neotropical electric knifefish genus Sternarchorhynchus (Apteronotidae; Gymnotiformes). The results support a hypothesis of Sternarchorhynchus as the sister group to Platyurosternarchus. A series of synapomorphies, many involving major innovations of the neurocranium, jaws, suspensorium, and associated systems that permit an unusual mode of grasp-suction feeding, support the monophyly of both genera. Synapomorphies largely resolve relationships within Sternarchorhynchus with basal nodes strongly supported by characters pertinent to prey capture and initial processing of food items. These possible key innovations may provide Sternarchorhynchus with a competitive advantage over other clades of the Apteronotidae and account for the species diversity of the genus in Neotropical rivers. Adaptive radiation in Sternarchorhynchus was analysed. Habitat preference transitions repeatedly occurred in the genus between deep-river channel dwelling species and rheophilic species with preferences for higher energy setting including rapids and swift-flowing fluviatile settings. Twenty-two species of Sternarchorhynchus are described as new based on samples that originated in the smaller rivers draining into the Golfo de Paria, the Marowijne and Essequibo River basins, the Río Orinoco and in particular the Amazon River basin. The 32 species in Sternarchorhynchus make it the most speciose genus in the Apteronotidae.No claim to original US government works. Journal compilation

Indeterminate body growth and lack of gonadal decline in the brown ghost knifefish (Apteronotusleptorhynchus), an organism exhibiting negligible brain senescence

“…In their natural habitat, these fish often suffer from damage to or loss of parts of the elongated, compressed caudal part of the body ("tail") because of predatory fish specialized in tail eating (Mago-Leccia et al 1985;Lundberg et al 1996;de Santana and Vari 2010). Probably in response to this selective pressure, gymnotiforms have developed the extraordinary ability to regenerate tails, including large parts of the caudal spinal cord, rapidly and with high efficiency-even after repeated loss of the tail (Sîrbulescu et al 2009;Zupanc 2011, 2013).…”

A New Species of Sexually Dimorphic Electric Knifefish from the Amazon Basin, Brazil (Gymnotiformes: Apteronotidae)

“…The neurocranium, suspensorium, and pectoral girdle were removed from all specimens using standard methods for the dissection of small teleosts (Weitzman, 1974). Osteological homology and nomenclature followed Hilton et al (2007) and de Santana and Vari (2010a), except for lateral line system nomenclature, which follow Arratia and Huaquin (1995) and de Santana and Crampton (2011).…”

“…Secondary sexual dimorphism, primarily involving variations in morphology of the head and snout of some mature males, is now known to be a common phenomenon within the Apteronotidae (Cox Fernandes, 1998;Cox Fernandes et al, 2002de Santana and Vari, 2010a). In this family, sexual dimorphism appears to have evolved independently several times (Rapp Py-Daniel and Cox Fernandes, 2005;Albert and Crampton, 2009;de Santana and Vari, 2010a).…”

“…In this family, sexual dimorphism appears to have evolved independently several times (Rapp Py-Daniel and Cox Fernandes, 2005;Albert and Crampton, 2009;de Santana and Vari, 2010a). In Apteronotus, seven species exhibit sexual dimorphism related to variations in head morphology of mature males.…”

A new species of the Eigenmannia trilineata (Gymnotiformes: Sternopygidae) species group from the río Orinoco basin, Venezuela

“…Approximately 50 species of gymnotiforms inhabit the río Orinoco basin (Mago-Leccia, 1994;Campos-da-Paz, 1995;Albert, 2003;Campos-da-Paz, 2003;de Santana, Crampton, 2007, 2011de Santana, Vari, 2009, 2010a, 2010bLundberg et al, 2013;Ivanyisky, Albert, 2014). Five species of Eigenmannia have been reported, among them: E. limbata, E.…”