BULLETIN OF THE FLORIDA STATE MUSEUM BIOLOGICAL SCIENCES Volume 5 Number 4 MIDDLE-AMERICAN POECILIID FISHES OF THE GENUS XIPHOPHORUS Donn Eric Rosen UNIVERSITY OF FLORIDA Gainesville 1960 The numbers of THE BULLETIN OF THE FLORIDA STATE MUSEUM, BIOLOGICAL SCIENCES, are published at irregular intervals. Volumes contain about 300 pages and are not necessarily completed in any one calendar year. OLIVER L. AUSTIN, JR., Editor WILLIAM J. RIEMER, Managing Editor All communications concerning purchase or exchange of the publication should he addressed to the Curator of Biological Sciences, Florida State Museum, Seagle Building, Gainesville, Florida. Manuscripts should be sent to the Editor of the BULLETIN, Flint Hall, University of Florida, Gainesville, Florida. Published 14 June 1960 Price for this issue $2.80 MIDDLE-AMERICAN POECILIID FISHES OF THE GENUS XIPHOPHORUS DONN ERIC ROSEN 1 SYNOPSIS. Drawing upon information from the present studies of the com- parative and functional morphology, distribution, and ecology of the forms of Xiphophorus (Cyprinodontiformes: Poeciliidae) and those made during the last quarter of a century on their genetics, cytology, embryology, endocrinology, and ethology, the species are classified and arranged to indicate their probable phylo- genetic relationships. Their evolution and zoogeography are considered in rela- tion to a proposed center of adaptive radiation on Mexico's Atlantic coastal plain. Five new forms are described: X. variatus evelynae, new subspecies; X. milleri, new species; X. montezurnae cortezi, new subspecies; X. pygmaeus nigrensis, new subspecies; X. helleri alvarezi, new subspecies. To the memory of MYRON GORDON, 1899-1959 for his quarter century of contributions to the biology of this and other groups of fishes. I This paper is a revision of a thesis presented to the Biology Department of the Graduate School of Arts and Sciences of New York University in partial fulfill- ment of the Ph.D. degree. The work was carried out while the author was associ- ated with New York University and the Genetics Laboratory of the New York Aquarium. It was supported by a National Science Foundation grant to the New York Zoological Society for Dr. Myron Gordon (project: A Biological Synthesis of the Poeciliid Fishes). Now at the University of Florida, the author serves the Department of Biology as Assistant Professor and the Florida State Museum as Assistant Curator of Natural Sciences. Manuscript submitted 24 July 1959. 58 BULLETIN FLORIDA STATE MUSEUM Vol. 5 TABLE OF CONTENTS PAGE Introduction - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 59 Acknowledgments - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 61 Materials and methods - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 62 The genus Xiphophorus - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 64 Accounts of the species and subspecies - - - - - - - - - - - - - - - - - - - - - - - - - 66 Xiphophorus couchianus (Girard) - - - - - - - - - - - - - - - - - - - - - - - - - - - 66 Xiphophorus maculatus (Guenther) - - - - - - - - - - - - - - - - - - - - - - - - - - 69 Xiphophorus variatus (Meek) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 78 Xiphophorus variatus xiphidium (Gordon) - - - - - - - - - - - - - - - - - - - - 81 Xiphophorus variatus variatus (Meek) - - - - - - - - - - - - - - - - - - - - - - - 84 Xiphophorus variatus evelynae, new subspecies - - - - - - - - - - - - - - - - - 87 Xiphophorus miller, new species - - - - - - - - - - - - - - - - - - - - - - - - - - - - 89 Xiphophorus montezumae Jordan and Snyder - - - - - - - - - - - - - - - - - - - 92 Xiphophorus montezumae montezumae Jordan and Snyder - - - - - - - - 93 Xiphophorus montezumae cortezi, new subspecies - - - 96 Xiphophorus pygmaeus Hubbs and Gordon - - - 98 Xiphophorus pygmaeus nigrensis, new subspecies - - - - - - - - - - - - - - 100 Xiphophorus pygmaeus pygmaeus Hubbs and Gordon - - - - - - - - - - - 102 Xiphophorus clemenciae Alvarez - - - - - - - - - - - - - - - - - - - - - - - - - - - 104 Xiphophorus helleri Heckel - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 106 Xiphophorus helleri helleri Heckel - - - - - - - - - - - - - - - - - - - - - - - - - 116 Xiphophorus helleri strigatus Regan - - - - - - - - - - - - - - - - - - - - - - - 118 Xiphophorus helleri guentheri Jordan and Evermann - - - - - - - - - - - - - 122 Xiphophorus helleri alvarezi, new subspecies - - - - - - - - - - - - - - - - - - 126 Distribution and ecology of Xiphophorus - - - - - - - - - - - - - - - - - - - - - - - - 156 Distribution patterns of Xiphophorus in relation to habitat preferences - - 156 Ecological restrictions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 156 Types of topographical and ecological isolation - - - - - - - - - - - - - - - 162 Adaptive modifications to the environment and patterns of distribution 169 Routes of dispersal - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 172 Relationships within Xiphophorus - - - - - - - - - - - - - - - - - - - - - - - - - - - - 175 Assessment of characters - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 175 Gonopodium - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 175 Pigmentation 180 Metamerism and body form in relation to habitat - - - - - - - - - - - - - - 182 Comparative behavior - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 188 Skeletal elements - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 189 Viability, development, and morphology of interspecific hybrids as systematic criteria in Xiphophorus - - - - - - - - - - - - - - - - - - - - 201 Embryonic development, fertility, and sexuality of interspecific hybrids in relation to their genetic background 201 Pigment cell abnormalities in hybrids - - - - - - - - - - - - -205 Abnormalities of the external genitalia of hybrids - - - - - - - - - - - - - - - 208 Species groups in Xiphophorus 212 The maculatus species group (couchianus, maculatus, variatus) 214 The montezumae species groups (milleri, montezumae, pygmaeus) - - - - 216 The helleri species group (clemenciae, helleri) - - - - - - - - - - - - - - - - - 218 Summary and conclusions - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 219 Appendix 1: Notes on meristic characters - - - - - - - - - - - - - - - - - - - - - - 223 Appendix 2: Key to the species Xiphophorus - - - - - - - - - - - - - - - - - - - - 226 Literature cited - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 229 1960 ROSEN: FISHES OF THE GENUS XIPHOPHORUS 59 INTRODUCTION The genus Xiphophorus (Cyprinodontiformes: Poeciliidae), which includes the platyfishes and swordtails, presents an exceptional op- portunity for taxonomic research. It is outstanding among fish groups in that its natural range is comparatively well known and its members adapt readily to laboratory conditions. During the last quarter cen- tury it has been the subject of an unusual number of diverse experi- mental and descriptive studies. Investigations of its genetics, cytol- ogy, embryology, endocrinology, and ethology have produced a back- ground of general biological information that gives an added per- spective to the basic morphologic and zoogeographic criteria of the tax- onomist. The objective of this revision is a systematic reappraisal of Xiphophorus that combines data from all these diverse yet comple- mentary fields. The following species and subspecies are recognized: Xiphophorus couchianus (Girard) (Northern platyfish) Xiphophorus maculatus (Guenther) (Southern platyfish) Xiphophorus variatus (Meek) (Variable platyfish) Xiphophorus variatus variatus (Meek) Xiphophorus variatus evelynae, new subspecies Xiphophorus variatus xiphidium (Gordon) Xiphophorus millet* new species (Catemaco livebearer) Xiphophorus montezumae Jordan and Snyder (Montezuma swordtail) Xiphophorus montezumae montezumae Jordon and Snyder Xiphophorus montezumae cortezi, new subspecies Xiphophorus pygmaeus Hubbs and Gordon (Pygmy swordtail) Xiphophorus pygmaeus pygmaeus Hubbs and Gordon Xiphophorus pygmaeus nigrensis, new subspecies Xiphophorus clemenciae Alvarez (Yellow swordtail) Xiphophorus helleri Heckel (Green swordtail) Xiphophorus helleri helleri Heckel Xiphophorus helleri strigatus Regan Xiphophorus helleri guentheri Jordan and Evermann Xiphophorus helleri alvarezi, new subspecies The formal generic separation of the swordtails (Xiphophorus Heckel, 1848) and the platyfishes (Platypoecilus Guenther, 1866) grew unchallenged out of early imperfect diagnoses of the species for which the two genera were first erected. Xiphophorus was applied by Heckel to three quite unrelated forms, X. helleri, Pseudoxiphophorus bimacu- latus, and Gambusia gracilis, a species of uncertain status. Weyen- burgh (1874) described three new forms as Xiphophorus Heckelii, X. obscurus and X. minor, species since assigned to the Jenynsiidae. For many years, Platypoecilus was misapplied to various cyprinodonti- forms, as follows: 60 BULLETIN FLORIDA STATE MUSEUM Vol. 5 Platypoecilus mentalis Gill (1876: 335) -= Mollienesia sphenops Cuvier and Valenciennes, a poeciliid. Platypoecaus quitzeoensis Been (1898: 540, 1 fig.) = Zoogoneticus quitzeoen- sis (Bean), a goodeid. Platypoecilus nelmni Meek (1904: 147, Fig. 46) = Mollienesia sphenops Cuvier and Valenciennes, a poeciliid. •Platypoecilus perugiae Evermann and Clark (1906: 851-52, Fig.