Relationships of the neon tetras, a group of South American freshwater fishes (Teleostei, Characidae), with comments on the phylogeny of New World characiforms

RELATIONSHIPS OF THE NEON TETRAS, A GROUP OF SOUTH AMERICAN FRESHWATER FISHES (TELEOSTEI, CHARACIDAE), WITH COMMENTS ON THE PHYLOGENY OF NEW WORLD CHARACIFORMS STANLEY H. WEITZMAN' and WILLIAM L. FINK^ CONTENTS Abstract 339 Introduction 339 Methods 340 S\stematics of the American Characidae 341 Imphcations of a Phylogenetic Classification of the Characiformes _ 346 A History of the Neon Tetra Problem 347 Paracheirodon Gery 353 Phylogenetic Analysis of Paracheirodon 353 Key to the Species of Paracheirodon 357 Paracheirodon simulans (Gery), 1963 358 Paracheirodon axelrodi (Schultz), 1956 367 Paracheirodon innesi (Myers), 1936 374 Discussion 379 Summary 381 Acknowledgments __ 383 Literature Cited 383 Appendix 1, Specimens Examined 386 Appendix 2, Type Localities of Species of Par-acheirodon 388 Appendix 3, Comments on Characters Currently Phylogenetically Uninformative 390 Abstract. The history of the classification and the relationships of the American Characidae is re-viewed in terms of phylogenetic principles. Current characid systematics is found unstable and unsatis-factory from typological and phylogenetic points of view. We predict that the classification of the Amer-ican characids and that of all characiforms will be subject to much reinterpretation and rearrangement through future phylogenetic analyses. The three known species of neon tetras are used ' National Museum of Natural History, Smithson-ian Institution, Washington, DC. 20560. 2 Museum of Comparative Zoology, Harvard Uni-versity, Cambridge, Massachusetts 02138. Present address: Department of Biology and Museum of Zo-ology, The University of Michigan, Ann Arbor, Michigan 48104. as an example of phylogenetic analysis within the American Characidae. This analysis exemplifies the difficulties of an initial phylogenetic study of a taxon with many ill-defined subgroups. These three species previously were placed in two characid subfamilies and three genera as follows: Hijphessohrycon simulans, the green neon, in the Tetragonopterinae; Cheirodon axelrodi, the cardinal tetra, and Paracheirodon innesi, the neon tetra, in the Cheirodontinae. Several synapomorphies were found to unite all three species, which are herein placed in Paracheirodon. The interrelationships among the three neon tetras are not resolved. INTRODUCTION The Characidae comprises the largest part of a group of freshwater fishes, the Characiformes, whose hving representa-tives are endemic to Africa and South and Central America. American characids are found from southern Argentina and Chile in South America north to the Mexico-United States border area in North Amer-ica. The greatest concentration of species occurs in the Amazon basin, the largest geographic area. There are fewer species to the north in the Orinoco basin and to the south in the Parana-Paraguay river system. Still fewer species occur in the nu-merous smaller drainage basins in Central America and peripheral to these three large river systems in South America. By the latest account, Gery (1977: 13-16), the American part of the family consists of 12 "subfamilies" and about 700 species, ex-cluding Serrasalminae and Characidiinae, both sometimes included within the Characidae. The phylogeny of these Bull. Mus. Comp. Zool., L50(6): 339-395, December 1983 339