Three New Species of the Neotropical Electric Fish Rhabdolichops (Gymnotiformes: Sternopygidae) from the Central Amazon, with a New Diagnosis of the Genus
Three new species of the Neotropical electric fish Rhabdolichops are described from the lowland Central Amazon Basin of Brazil. These taxa are described using features of color pattern, morphometric and meristic traits, squamation, and osteology. Rhabdolichops nigrimans and R. navalha are known only from low-conductivity blackwater systems whereas R. lundbergi occurs almost exclusively in the main channel of high-conductivity whitewater rivers and adjacent floodplain channels. Rhabdolichops nigrimans and R. lundbergi are sister species, forming a sister clade to all other Rhabdolichops species, and retaining transitional phenotypes between the genera Eigenmannia and Rhabdolichops. Rhabdolichops nigrimans, but not R. lundbergi, displays a striking sexual dimorphism in caudal appendage length. Rhabdolichops navalha and R. stewarti are sister species nested within a clade comprising R. eastwardi and R. caviceps + R. troscheli. Rhabdolichops navalha exhibits a unique morphology of the electric organ where the posterior margin ends abruptly and is replaced posteriorly by rigid and transparent non-electrogenic tissue. Três espécies novas de peixes elétricos neotropicais, Rhabdolichops, são descritas da bacia Amazônica, Brasil. Estas espécies são descritas com base em características de pigmentação, morfologia, osteologia e dados merísticos. Rhabdolichops nigrimans e R. navalha são conhecidos exclusivamente de sistemas de águas pretas com condutividade baixa. Rhabdolichops lundbergi ocorre quase exclusivamente nas calhas principais dos rios de águas brancas e em canais de várzea (paranás) com condutividade alta. Rhabdolichops nigrimans e R. lundbergi formam um clado monofilético que representa um grupo irmão das demais espécies de Rhabdolichops. Estas duas espécies apresentam fenótipos transicionais entre os gêneros Eigenmannia e Rhabdolichops. Rhabdolichops nigrimans apresenta um dimorfismo sexual acentuado no comprimento do filamento caudal. Contudo, R. lundbergi não possui esta característica. Rhabdolichops navalha e R. stewarti são espécies irmãs dentro de um grupo monofilético constituido por R. eastwardi e R. caviceps + R. troscheli. Rhabdolichops navalha apresenta uma morfologia única do órgão elétrico onde a sua margem posterior finda-se abruptamente e é substituída, posteriormente, por um tecido rígido e não-eletrogênico.Abstract
Photographs of preserved specimens of the holotypes of three new species of Rhabdolichops.(A) R. nigrimans (female, MCP 36048). (B) R. lundbergi (male, MCP 36037). (C) R. navalha (immature, MCP 36046). Scale bar = 10 mm
Photographs of heads of live specimens of three new species of Rhabdolichops.(A) R. nigrimans (female, MCP 36052). (B) R. lundbergi (immature, MCP 36044). (C) R. navalha (immature, INPA 15782). Scale bar = 5.0 mm
Camera lucida tracing of opercle (left side in lateral view).(A) Rhabdolichops nigrimans. (B) R. lundbergi. Scale bar = 1.0 mm
Camera lucida tracing of displaced hemal spines (left side in lateral view).(A) Rhabdolichops nigrimans. (B) R. navalha. Labeled vertebrae number are counted in an anterior to posterior direction and include those of Weberian apparatus. Scale bar = 1.0 mm
Phylogenetic relationships of Rhabdolichops species and representative species of all other sternopygid genera (S = Sternopygus, A = Archolaemus, D = Distocyclus, E = Eigenmannia).Topology is a strict consensus of six equally parsimonious trees consistent with the data matrix of Table 2, with all characters weighted equally. Each tree: length = 55, consistency index (CI) = 0.80, retention index (RI) = 0.90, rescaled consistency index (RC) = 0.72. Numbers on nodes: unambiguous branch length/Bremer decay index/bootstrap values. Bootstrap values <70% are indicated with “–”
Contributor Notes
(SBC) Department of Zoology, University of Florida, Gainesville, Florida 32611-7800; (WGRC) Florida Museum of Natural History, University of Florida, Gainesville, Florida 32611-7800; (JSA) Department of Biology, University of Louisiana at Lafayette, Lafayette, Louisiana 70504-2451. (JSA) jalbert@louisiana.edu Send reprint requests to JSA