The Systematics of the Frogs of the Hyla Rubra Group in Middle America Part 1

The Systematics of the Frogs of the Hyla Rubra Group in Middle America.

by Juan R. Leon.

INTRODUCTION

The tree frogs of the _Hyla rubra_ group are abundant and form a conspicuous element of the Neotropical frog fauna. Representatives of the group occur from lowland Mexico to Argentina; the greatest diversity is reached in the lowlands of southeastern Brazil (Cochran, 1955). The group apparently originated in South America; the endemic Central American species evolved from stocks that invaded Middle America after the closure of the Colombian Portal in the late Pliocene.

Dunn (1933) partially defined the _rubra_ group as it occurs in Central America. Cope (1865, 1876, 1887), Brocchi (1881), Boulenger (1882), Gunther (1901), n.o.ble (1918), Kellogg (1932), Dunn and Emlen (1932), Stuart (1935), and Gaige (1936) dealt with the Middle American species now considered to make up the _rubra_ group. More recently, Taylor (1952, 1958), Fouquette (1958), Starrett (1960), and Duellman (1960, 1963, 1966a) studied aspects of the taxonomy and biology of the species of this group. The five species of the _rubra_ group in Central America have received ten different names. One species, _Hyla staufferi_, has received five names (two subspecies are recognized herein). _Hyla boulengeri_ was named in the genus _Scytopis_, but the type species of _Scytopis_ is a member of the genus _Phrynohyas_ Fitzinger, 1843 (Duellman, 1956.)

Little has been published concerning the ecology, life history, osteology, and mating calls of the Middle American species of this group. The purpose of the present report is to describe the species occurring in Middle America and to comment on their distributions, ecology, cranial osteology, and mating calls, and in so doing provide evidence for the evolutionary history of the species inhabiting Middle America.

Acknowledgments

For permission to examine specimens in their care, I am grateful to Drs. Richard G. Zweifel, American Museum of Natural History (AMNH); Robert F. Inger, Field Museum of Natural History (FMNH); Ernest E.

Williams, Museum of Comparative Zoology (MCZ); Hobart M. Smith, University of Illinois Museum of Natural History (UIMNH); Charles F.

Walker, University of Michigan Museum of Zoology (UMMZ); Jay M. Savage, University of Southern California (USC); James A. Peters, United States National Museum (USNM); Richard J. Baldauf, Texas Cooperative Wildlife Collection (TCWC); and W. Frank Blair, Texas Natural History Collection (TNHC). KU refers to specimens in the Museum of Natural History, University of Kansas. For the loan of tape-recordings of mating calls I thank Drs. W. Frank Blair, University of Texas, and Richard G. Zweifel, American Museum of Natural History.

I am indebted to the Ford Foundation-Universidad de Oriente (Venezuela) Science Project for a scholars.h.i.+p which enabled me to study for two years at The University of Kansas, foster inst.i.tution of the project. I have benefited by being able to work in the Museum of Natural History at The University of Kansas and I am grateful to Dr. E. Raymond Hall, Director, for providing s.p.a.ce and equipment.

I gratefully acknowledge the a.s.sistance and advice of Dr. William E.

Duellman, who suggested and directed this work, made available specimens under his care and gave much of his time in reading the ma.n.u.script and suggesting improvements. I am grateful to Dr. Frank B.

Cross who critically read the ma.n.u.script and made many editorial suggestions. I am indebted to Linda Trueb for a.s.sistance with the osteological aspects of this study; she helped to clarify many confusing points. I am grateful to Charles W. Myers for making available his field notes on these frogs in Panama, to Arthur C.

Echternacht for reading part of the ma.n.u.script, and to John D. Lynch for many suggestions and helpful criticisms. The ill.u.s.trations were executed by David M. Dennis.

Materials and Methods

For the purposes of the present study I examined 1383 preserved specimens, 50 skeletons, and 9 lots of tadpoles. External characteristics used in the a.n.a.lysis of variation are those currently employed in the study of anuran systematics. Twelve measurements and six proportions were taken in the manner described by Duellman (1956). Only the most important references are given in the synonymies, except those of the two subspecies of _Hyla staufferi,_ which are more nearly complete. The taxonomic history of each frog is discussed under _Remarks_ in each account. The cranial osteology was studied by using skeletons and cleared and stained specimens of all species.

Developmental stages of tadpoles were determined from Gosner's (1960) table. Personal field work in Central America in the summer of 1966 provided an opportunity to make observations on the ecology, calling sites, and color in life; these data were supplemented by field notes from, and discussions with, Dr. William E. Duellman and Charles W.

Myers.

The mating calls of the frogs were recorded in the field on Magnemite and Uher Tape Recorders by Dr. Duellman in the course of his work on the hylid frogs of Middle America--supported by grants from the National Science Foundation (G-9827 and GB-1441). These recordings, plus those borrowed from other inst.i.tutions, provided 50 tapes for a.n.a.lysis of the mating calls. The calls were a.n.a.lyzed on a Vibralyzer (Kay Electric Company).

THE HYLA RUBRA GROUP

_Definition._--The species forming the group are small to moderate-sized tree frogs (maximum snout-vent length of males of various species 20-49 mm.), distinguished from other groups in the genus _Hyla_ as follows: Brown, grayish brown, or yellowish tan above; thighs plain, marbled with dark brown, or having vertical bands; vocal sac single, median, subgular; snout flat, protruding, rounded or pointed; webbing between fingers reduced or absent; web between first and second toes reduced to fringe on second toe, rest of toes about half webbed; tarsal fold reduced or absent; shanks robust; inner metatarsal tubercle larger than outer; prevomerine teeth on transverse ridges between small to large sized choanae; skull generally longer than wide; nasals large (length more than 40 per cent total length of skull) and having pointed maxillary processes; maxillary bearing small ventromedial palatine process; quadratojugal slender, always joined to maxillary by bony suture; auditory region of prootic slender and short; delicate spatulate columella ventral to crista parotica, broad basally, compressed anterolaterally, slightly rounded distally; anterior arm of squamosal extending about half distance to maxillary; sphenethmoid wider than long; frontoparietal fontanelle present or absent; prevomerine, premaxillary, and maxillary teeth present; prevomer with two lateral processes forming incomplete bony margin to internal nares; tadpoles having pointed xiphicercal tail, snout short, rounded; 2/3 tooth rows; dorsal fin deeper than ventral fin; sinistral spiracle; short dextral a.n.a.l tube not reaching edge of ventral fin; mating calls consisting of single long note or series of short notes.

_Composition._--This group contains about 24 currently recognized species, most of which occur in Brazil. Only five species--_boulengeri,_ _elaeochroa_, _foliamorta_, _rubra_, and _staufferi_ with two subspecies--occur in Central America. _Hyla boulengeri_ and _rubra_ are widespread in South America, and _foliamorta_ occurs in Colombia, whereas the other species are known only from Middle America.

_Distribution._--The species of the _Hyla rubra_ group range from the lowlands of northern Argentina and Bolivia to southern Tamaulipas and Guerrero, Mexico.

_Comments._--In Central America two subgroups of species can be recognized. _Hyla boulengeri_ and _H. foliamorta_ are distinctive in the large size of adults (snout-vent lengths 41-49 mm.); both have prominent bars on the thighs, a well-defined interorbital triangular mark, blotches or spots dorsally, and large choanae. _Hyla elaeochroa,_ _H. rubra,_ and _H. staufferi_ are smaller (snout-vent lengths 29-40 mm.); they have the thighs weakly barred or vermiculate anteriorly and posteriorly or unmarked, an ill-defined interorbital triangular mark, linear markings dorsally, and small choanae.

Key to Species and Subspecies

1. Larger frogs (males to 49 mm. snout-vent length); thighs strongly barred; supratympanic fold black; dorsum blotched or spotted 2

Smaller frogs (males to 40 mm. snout-vent length); thighs weakly barred or plain; supratympanic fold pale brown; dorsum usually having linear pattern 3

2. Dorsum tuberculate; snout subac.u.minate; vocal sac flecked with brown; tarsal fold rudimentary; web absent between fingers; black spots absent in scapular region _H. boulengeri_

Dorsum smooth; snout pointed; vocal sac dark gray; tarsal fold absent; trace of web between fingers; two or more elongate dark spots in scapular region _H. foliamorta_

3. Snout-vent length more than 30 mm.; tympanum 2/3 to 3/4 diameter of eye; prevomerine elevations about size of choanae 4

Snout-vent length less than 30 mm.; tympanum less than 1/2 diameter of eye; prevomerine elevations smaller than choanae 5

4. Thighs mottled posteriorly; discs on fingers about 1/2 size of tympanum; faint dark line from nostril to eye _H. rubra_

Thighs faintly barred or plain posteriorly; discs on fingers about size of tympanum; distinct dark line from nostril to eye _H. elaeochroa_

5. Dorsum brown with irregular dorsolateral stripes and interrupted paravertebral stripes; two transverse bars on shanks; interorbital bar present _H. staufferi staufferi_

Dorsum gray with complete dorsolateral and paravertebral stripes; longitudinal stripe on shank; interorbital bar absent _H. staufferi altae_

Key to Known Tadpoles

1. Entire lower beak black; beaks moderate-sized, serrate; dorsal fin high, extending to middle of back 2

No more than half of lower beak black; beaks small, finely serrate; dorsal fin lower, barely extending onto body 3

2. Papillae present only laterally _H. boulengeri_ Papillae present laterally and ventrally _H. foliamorta_

3. Distinct brown stripe from nostril to eye; two stripes below eye, _H. elaeochroa_

Faint stripe from nostril to eye; no stripe below eye _H. staufferi_

ACCOUNTS OF SPECIES AND SUBSPECIES

_Hyla boulengeri_ (Cope)

_Scytopis boulengeri_ Cope, Bull. U.S. Natl. Mus., 32:12, December 1, 1887 [Holotype.--USNM 13974, from "Nicaragua"; J. A. McNiel, collector].

_Hyla boulengeri:_ Gunther, Biologia Centrali-Americana, Reptilia and Batrachia, p. 267, June 1901. n.o.ble, Bull. Amer. Mus. Nat.

Hist, 38:339, June 1918. Taylor, Univ. Kansas Sci. Bull., 35:856, July 1, 1952.