A threatened new species of Oligosarcus and its phylogenetic relationships, with comments on Astyanacinus (Teleostei: Characidae)

Abstract

Oligosarcus itau n. sp. is described. This species is the sister group of the remaining analyzed species of Oligosarcus and this relationship is supported by seven morphological synapomorphies: 1) well developed temporal fossa, 2) absence of a dorsal expansion on the rhinosphenoid, 3) posteroventrally angled articulation between second and third infraorbitals, 4) presence of ectopterygoid teeth on a row, 5) laterally displaced cartilage on the ectopterygoid, 6) presence of bony lamellae bordering laterosensory canal of suprapreopercle, and 7) presence of two pairs of uroneurals. The new species is diagnosed by the following combination of characters: 1) two distinct premaxillary rows of teeth, 2) tricuspidate and pentacuspidate teeth on dentary and posterior premaxillary row, 3) presence of a row of 3–4 tricuspidate to conical ectopterygoid teeth, 4) possession of v-vi,21–23 anal-fin rays, and 5) presence of 41–42 perforated scales on lateral line. Oligosarcus itau n. sp. was previously considered as an Astyanacinus. Astyanacinus moorii (Boulenger), type species of the genus, is included in the Astyanax clade and Astyanacinus platensis Messner is transferred to Oligosarcus.

A New Miniature Characid (Ostariophysi: Characiformes: Characidae), with Phylogenetic Position Inferred from Morphological and Molecular Data

“…Despite the morphological similarities between Erythrocharax and the aforementioned genera and the Cheirodontinae of Malabarba [21], phylogenetic analyses including the new taxon in Mirande's [4] data matrix (with additions of Mirande et al [13], and Malabarba et al [14]) results in the genus being deeply nested in the Characidae of Mirande [4], and included with Rhoadsiinae, as the sister group of a clade comprised by (Cheirodontinae+(Aphyoditeinae+(Aphyocharacinae+Stevardiinae))) (complete tree available as Figure S1). This group is supported by five synapomorphies common to all fundamental trees obtained in the traditional search with equal weights: the sphenotic spine not extending ventrally to the articulation between the sphenotic and hyomandibula (Char.…”

“…Thus, the new taxon described herein presents three distinct alternative hypotheses of relationships: one based on the presence of the diagnostic characters of the Cheirodontinae as proposed by Malabarba [21]; the second based on morphological characters following Mirande [4] and Mirande et al [13]; and the third based on molecular data [9]. Therefore, the exclusion of Erythrocharax from any recognized genus in Characidae by all three approaches, as well as the definitions of the genera following classical studies such as those of Eigenmann [26], underpins the current decision to erect a new name for the described taxon.…”

“…Such robustness should not only include the use of advanced methodological approaches to reduce biased topologies, but also extended towards taxa and character sampling, in an attempt to produce more stable phylogenetic hypotheses. At this time, ichthyologists stand at a point where less than 20% of the characid diversity has been included in any morphological and/or molecular analyses [4], [8], [9], [13], and these studies do not represent the complete picture of relationships within the family.…”

“…The morphologic phylogenetic study follows Mirande's [4] framework with the posterior additions of Mirande et al [13] and Malabarba et al [14], whereas the molecular phylogeny methodology (data production and analysis) is based in Oliveira et al [9] and the results of Tagliacollo et al [15] and Mariguela et al [16]. The cladistic analysis of the morphological dataset was performed with aid of the software Tree analysis using New Technology – TNT, licensed to the Willi Hennig Society [17] using the heuristic search algorithim “Mult” with 5000 replicates, using the TBR branch swap algorithm.…”

“…laterosensory canal system of absent infraorbitals; modifications of the rhinosphenoid) were coded as inapplicable, contrary to Mirande [4], who attributed states to characters fitting these conditions. The complete coding for Erythrocharax altipinnis following character sequence presented in Mirande [4] and subsequently modified by Mirande et al [13] is presented in Table S1. All sequences obtained were deposited in GenBank under the accession numbers: 16S: JX570761, CytB: JX570762, Myh6: JX570763, Rag2: JX570764.…”