BULLETIN OF THE FLORIDA STATE MUSEUM BIOLOGICAL SCIENCES Volume 5 Number 4 MIDDLE-AMERICAN POECILIID FISHES OF THE GENUS XIPHOPHORUS Donn Eric Rosen fR \/853 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 be addressed to the Curator of Biological Sciences, Florida State Museum, Seagle Building, Gainesville, Florida. Manuscripts should be sent to the Editor of the B ULLETIN, 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: R6eciliidae) 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. varidtus evelynae, new subspecies; X, milleri, new specie-s; X. montezumae cortezi, new subspecies; X. pygmaeus 'nigrensis, new ' subspecies; X. heHeri aluarezi, new subspecies. To the memory of MYR6N GORDON, 1899-1959 for his quarter century of contributibns- to the biology of this and other groups of fishes. 1 This paper is a revision of a thesis prehented to the Biology Department of the Graduate School of Arts and Sciences of New York University in partial fulfill- ment of the P.h.D. degree. The w6rk 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 Zo6logical 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. S 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 uariatus uariatus (Meek) - 84 Xiphophorus uariatus evelynae, new subspecies 87 Xiphophorus mitleri, new species 89 Xiphophorus montezumae Jordan and Snyder - 92 Xiphophorus montezunme montezumae Jordan and Snyder -- 98 Kiphophorus montezumae cortezi, new subspecies - 96 Xiphophorus Pugmaeus Hubbs and Gordon 98 Xiphophorus pugmdeus nigrensts, new .subspecies 100 Xiphophorus pygmaeus pugmaeus Hubbs and Gordon __._._--_--_---____ 102 Xiphophorus clemenciae Alvarez 104 Xiphophorus helleri Heelzel 106 Xiphophorus helleri helleri Heckel 116 Xiphophorus helleri strigatus Regan _ 118 Xiphophorus hetteri guentheri Jordan and Evermann - 122 Xiphophorus hetteri aluarezi, 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 Relationships within Xiphophorus - ---- - - 175 Assessment of characters 175 Gonopodium 175 Pigmentation - --- u . · - 180 Metamerism and body form in relatiOn to habitat ~ 182 Comparative behavior f88 Skeletal elements 189 Viability, development, abd 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, uariatus) 214 The montezumae species groups (milleri, montezumae, pygmaeus) 216 The helleri species group (clemenciae, helleri) · - 218 Summary and contldions - 210 Appendix 1: Notes on meristic characters 228 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 ex6epti6nal 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- irientary fields. The following species and subspecies are recognized: Xiphophorus col,chianus (Girard) (Northern platyfish) Xiphophorus maculatus (Guenther) (Southern platyfish) Xiphophorus uariatus (Meek) (Variable platyfish) Xiphophorus Uariatt,5 1>afiatus (Meek) Xiphophorus variatus evelynae, new subspecies Xiphophorw vanatus *iphidium (Gordon) Xiphophorus millmi, 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 pvgmaeus pygmaeus Hubbs and Gordon Xiphophorus P!/~maeus nigrensis, new subspecies Xiphophorus c~emendiae Alvarez (Yellow swordtail) Xiphophorus hetteri Heckel (Green swordtail) Xiphophorus hetteri helleri Heckel Xiphophorus helleri strigatus Regan Xiphophorus heneri guentheri Jordan and Evermann Xiphophorus hetteri aluarezi, 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 thetwo 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) describad 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 fcillows: 60 BULLETIN FLORIDA STATE MUSEUM Vol. 5 Platypoecilus mentalis Gill (1876: 885) = Mollienesia sphenops Cuvier and· · Valenciennes, a poecihid. I Platypoecitus quitzeoensis Bean (1898: 540, 1 fig.) - Zoogoneticus quitzeoen- : sis (Bean), a goodeid. Platypoecilus netsoni Meek (1904: 147, Fig. 46) = Mollienesia sphenops Cuvier and Valenciennes, a poeciliid. Platypoecitus perugiae Evermann and Clark (1906: 851-52, Fig. 1) - Limia perugiae (Evermann and Clark), a poeciliid. Platypoecilus dominicensis Evermann and Clark (1906: 852-58, Fig. 2) - Mollienesia (Ps!/chropoecilia) dominicensis (Evermann and Clark), a poeciliid. Platt/Poecitus tropicus Meek (1907: 146-47) = Mollienesia sphenops Cuvier and Valenciennes, a poeciliid. The above ,corrections in identification were indicated by Meek (1902, 1904), Regan (1907, 1918), and Myers (1985). Not until the gonopodial characters of the Poeciliidae were thoroughly studied (Regan, 1913) were the felationships of Plat!/poecilus demonstrated. - Early knowledge of Xiphophorus came largely from its comparison with Poecilia and Mollienesia to which .some thought it bore a close relationship. The delimiting criteria for Poecilia eventually served also, in part, for Xiphophorus. When Platypoecilus was named dur- ing this early period and separated nomenclaturally from Poecilia and its allies, it was natural to regard Platypoetilus.and Xiphophorus as distinct. Summarizing the historical events up to 1911, three distinct groups of Xiphophorus (as pfesently constituted) were formally recognized, largely on ~ the basis of their fin structure and dentition. 1) Both helleri and montezumae possess the the caudal appendage or sword and biserial dentition (Xiphophorus); 2) maculatus and uariatus lack a sword and have but a single series of small teeth (Platypoetilus); 3) couchianus also lacks the sword but possesses biserial dentition (Po- ecilia). Regan (1913) decided that the species of Platypoecilus and Xiph- ophorus, which previously had been widely separated, were in reality closely related. He also showed that the alleged dentitional differ- ences in the two genera are not real, and that all the members of both genera do, in fact, have biserial dentition, a fact which was Dresaged when he (1907) distinguished between an outer row and inner band