The Characidiinae: A phylogenetic study of the South American darters and their relationships with other Characiform fishes.

Abstract

The Characidiinae is a group of Neotropical fishes inhabiting in most river drainages between eastern Panama and eastern Argentina (35$\sp\circ$ S). The monophyly of the subfamily, the interrelationships of its species, and its relationships with other Characiformes are investigated using cladistic methodology. Monophyly of the Characidiinae is supported by 13 synapomorphies, including presence of a gap between the dentary and angulo-articular bones, a medial process on the rib of the fifth vertebra located ventral to the swim bladder, and a large block of cartilage separating the vomer from the mesethmoid. Of 58 previously proposed nominal species, 50 are recognized as valid. Ten additional species are described as new. These species are more closely related to the type species of Ammocryptocharax, Klausewitzia, and Elachocharax, than to Characidium fasciatum, type species of Characidium. The genera Characidium and Klausewitzia as previously defined are polyphyletic. Four new genera are proposed in a monophyletic classification of the Characidiinae. C. blennioides and C. rex are excluded from Characidium and included in a new genus along with six new species. Miniaturization, the presence of numerous apparently paedomorphic characters associated with reduced body size, is identified as an important aspect of characidiin evolution. Eleven species are recognized as miniatures. Based on phylogenetic criteria, three independent miniaturization events are hypothesized within Characidiinae. Reductive characters represent an important factor in phylogeny reconstruction, accounting for more than half of the character-state transformations affecting supraspecific relationships among Elachocharax, Klausewitzia and two newly proposed genera. The Crenuchinae is identified as the sister group of the Characidiinae based on parsimony analysis of relationships among characiform fishes. These taxa compose the Crenuchidae, which is diagnosed by (1) midsagittal cranial fontanel restricted to the area posterior to epiphyseal bar; (2) ectopterygoid teeth present; (3) absence of superneural preceding neural spine of fourth vertebra; (4) absence of interosseous space between coracoid and cleithrum; (5) two or more unbranched rays on leading edge of pectoral fin; (6) presence of lateral frontal foramina located posterodorsal to orbit.