Osteology of Priocharax and Remarkable Developmental Truncation in a Miniature Amazonian Fish (Teleostei: Characiformes: Characidae)

Author(s)

Mattox, George M. T. ^{[1, 2]} ; Britz, Ralf ^[3] ; Toledo-Piza, Monica ^[1]

Affiliation

^[1] Univ Sao Paulo, Dept Zool, Inst Biociencias, BR-05508090 Sao Paulo - Brazil

^[2] Univ Fed Sao Carlos, Dept Biol, Campus Sorocaba Rodovia Joao Leme dos Santos SP 2, BR-18052780 Sorocaba, SP - Brazil

^[3] Nat Hist Museum, Dept Life Sci, Cromwell Rd, London SW7 5BD - England

• Document type: Journal article
• Source: Journal of Morphology; v. 277, n. 1, p. 65-85, JAN 2016.
• Web of Science Citations: 6

Abstract

Establishing phylogenetic relationships of miniature fishes is challenging in taxa with developmental truncation. Within the Characiformes, developmental truncation appears to be relatively rare, with the Neotropical genus Priocharax being an example. Priocharax includes three miniature species among the smallest of the order and has been hypothesized to belong to the Heterocharacinae. The pronounced reduction in its skeleton, however, prevented a clearer evaluation of its relationships. The present detailed osteological study was designed to address this question and revealed that 21 bones are absent and nine other skeletal structures are simplified in Priocharax when compared to other characids. Comparison of the skeleton of adult Priocharax with early developmental stages of other characids demonstrated that most of the absences and simplifications can be interpreted as developmental truncations. The most striking developmental truncations are in the pectoral girdle, in which the endoskeleton remains entirely cartilaginous. Other interesting truncations are in the ethmoid region of the skull, infraorbital series, and Weberian apparatus, in which the claustrum is absent. Our study also revealed some unusual sexual dimorphisms in the pelvic girdle. Two cladistic analyses were performed to assess the relationships of Priocharax within the Heterocharacinae. The first consisted of a traditional analysis in which all absences and reductions of Priocharax were coded in the same way as in the remaining taxa. This resulted in three equally most parsimonious topologies, all of which have Priocharax as the most basal taxon of the Heterocharacinae. The second analysis incorporated ontogenetic information, and most absences and reductions of Priocharax were reinterpreted as apomorphic conditions and thus, coded differently from similar conditions in outgroups. This resulted in a single phylogenetic hypothesis with Priocharax and Gnathocharax as sister groups based on seven synapomorphies. Our approach demonstrates the importance of developmental studies to better understand morphological evolution of miniaturized, truncated taxa, and to generate hypotheses of their relationships. (C) 2015 Wiley Periodicals, Inc. (AU)

• FAPESP's process: 11/50282-7 - An inventory of the Characiform fish fauna (Teleostei, Ostariophysi) from South America
• Grantee: Naercio Aquino Menezes
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 11/13735-3 - Collecting, maintaining and preserving specimens of miniature fishes and obtaining ontogenetic series of fishes: the importance of these steps for ensuring successful results in studies of the process of miniaturization
• Grantee: Mônica de Toledo-Piza Ragazzo
• Support Opportunities: Research Grants - Visiting Researcher Grant - International
• FAPESP's process: 12/01075-1 - Proposal of research internship abroad associated with the pos-doc project Phylogenetic Study of Priocharax Weitzman & Vari (Teleostei, Characiformes, Characidae) in the Ontogenetic Context: an Approach of the Miniaturization Process
• Grantee: George Mendes Taliaferro Mattox
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor