A Review of the Frogs of the Hyla bistincta Group Part 1

A Review of the Frogs of the Hyla bistincta Group.

by William E. Duellman.

INTRODUCTION

In the mountainous regions of Middle America there are several groups of hylid frogs that inhabit mountain streams. Some of these groups, such as _Plectrohyla_ and _Ptychohyla_, have been elevated to generic rank, whereas others are retained in the large and complex genus _Hyla_. In the mountains of Mexico five species of hylids that seem to compose a phyletic unit are herein referred to as the _Hyla bistincta_ group. Since 1955 I have been acc.u.mulating specimens of, and data on, this group with the result that all specimens known to me, including the types of all named taxa, have been studied. Detailed observations have been made on the ecology and life histories of three of the species; the other two species are known to me only from preserved specimens.

Acknowledgments

For permission to examine specimens in their care I am indebted to Charles M. Bogert, American Museum of Natural History (AMNH); Doris M. Cochran, United States National Museum (USNM); Jean Guibe, Museum National d'Histoire Naturelle, Paris (MNHN); Robert F. Inger, Chicago Natural History Museum (CNHM); Hobart M. Smith, University of Illinois Museum of Natural History (UIMNH); Charles F. Walker, University of Michigan Museum of Zoology (UMMZ). (Abbreviations of inst.i.tutions given above in parentheses are used throughout; the Museum of Natural History, University of Kansas is abbreviated KU.)

For their willing a.s.sistance in the field I am grateful to Ann S.

Duellman, Dale L. Hoyt, and John Wellman. Permits for collecting in Mexico were generously issued by the late Ing. Luis Macias Arellano, Departamento de la Fauna Silvestre, Direccion General de Caza. The drawings in figures 1 and 3 were executed by Gail Selfridge. This research has been supported by the National Science Foundation (NSF G-9827).

THE HYLA BISTINCTA GROUP

The five species comprising the _Hyla bistincta_ group are moderate-sized hylids having rather blunt heads and robust bodies.

The fingers are long and have little webbing (Fig. 1). The skin of the dorsum is thick and glandular, but not tuberculate. An a.n.a.l sheath is present. The skull is rather broad, flat, and solidly roofed. The ethmoid is broad, curved downward laterally, and solidly sutured to the frontoparietal. The nasals are broad, sutured for their entire width with the ethmoid, and broadly in contact medially. The premaxillaries are in contact medially; each has a long, flat nasal process. The quadratojugal is absent, and the maxillary tapers to a point posteriorly. There is no squamosal-maxillary connection.

The maxillary and premaxillary teeth are rather long, bifid, and moderately spatulate. Some teeth on the premaxillary and anterior part of the maxillary are hooked. The vomerine teeth are spatulate and bifid. A broad, flat, ossified prepollex is present but does not project as a spine. The known tadpoles have ventral mouths, 2/3 tooth-rows, two or more rows of l.a.b.i.al papillae, and long tails with low fins.

[Ill.u.s.tration: FIG. 1. Palmar view of right hand of: _a._--_Hyla robertsorum_ (KU 57661), _b._--_Hyla charadricola_ (KU 58414). 3.]

As thus defined the _Hyla bistincta_ group can be distinguished from all other groups of Middle American frogs by the combination of absence of the quadratojugal, non-projecting prepollex, long fingers with little webbing, and stream-inhabiting tadpoles having 2/3 tooth rows and two or more rows of l.a.b.i.al papillae.

Possibly _Hyla arborescandens_ and _Hyla hazelae_ belong in this group. Because these species are somewhat different from the included species and because their tadpoles are as yet unknown, I have refrained from including these two species in the _Hyla bistincta_ group. Taylor (1948:261) a.s.signed _Hyla proboscidea_ (= _H.

dalquesti_) and (1949:272) _Hyla cyclomaculata_ to this group, but because these two species have a quadratojugal and notably different tadpoles, they are excluded from the group.

Frogs of the genus _Plectrohyla_ closely resemble species in the _Hyla bistincta_ group but differ princ.i.p.ally in having a projecting prepollex. In the highlands of Costa Rica a group of species, of which _Hyla moesta_ is best known, resembles species in the _Hyla bistincta_ group. At present insufficient information is available on the Costa Rican species to determine their affinities.

a.n.a.lysis of Characters

The characters used in the systematic study of the frogs in this group are those usually employed in anuran systematics. Of the various measurements and proportions, the snout-vent length and the relative size of the tympanum to the eye apparently are of more taxonomic importance than the others (Table 1). In all of the species the tympanum is at least partially covered by a heavy, dermal supratympanic fold, and in some specimens of _H. pachyderma_ the tympanum is completely obscured. In two species (_H. bistincta_ and _H. charadricola_) the snout is square, whereas in the other species it is round.

The fingers are long and slender in _H. cra.s.sa_, _pachyderma_, and _robertsorum_ and somewhat shorter with more webbing in _H. bistincta_ and _charadricola_. Breeding males of _Hyla pachyderma_ have moderately large nuptial spines; the other species have small spines, except _H. charadricola_ in which spines apparently are absent. A well-defined thoracic fold is present in _H. pachyderma_, and a weak fold is present in _H. robertsorum_; the other species lack folds. In all species there is an a.n.a.l sheath; this sheath is longest in _H.

bistincta_, in which the a.n.a.l opening is directed ventrally at the level of the lower edge of the thighs.

Frogs in this group are rather drab in appearance. The dorsal color varies from dull green to various shades of brown. The most distinct aspect of the coloration is the different color patterns on the flanks and posterior surfaces of the thighs. The flanks in all species are marked with spots or reticulations.

_Hyla bistincta_ differs from other members of the group in having vocal slits and a distensible vocal sac. Only this species has been reported to call (Shannon, 1951:473). Insofar as is known, the other species are mute. Examination of skeletal preparations of _H.

bistincta_, _charadricola_, and _robertsorum_ and X-rays of the other species shows no notable specific differences in the osteology. Since the tadpoles of only _H. bistincta_ (Duellman, 1961:47) and _H.

robertsorum_ (Rabb and Mosimann, 1955) are known, larval characters are of limited use in intra-group systematics.

Key to the Species of the _Hyla bistincta_ Group

1. Snout, in dorsal profile, short and bluntly rounded; canthus rounded, sometimes indistinct, vocal slits absent 2

Snout, in dorsal profile, longer, squared; canthus distinct, vocal slits present or absent 4

2. Feet webbed to base of discs; dorsum dull olive green; flanks having cream-colored spots _H. cra.s.sa_, p. 486

Feet not webbed to base of discs; dorsum brown 3

3. Tarsal fold strong; thoracic fold heavy; webbing on feet extending to middle of penultimate phalanx of fourth toe; distinct white stripe above a.n.u.s; cl.u.s.ter of largo spines on thumb in breeding males, _H. pachyderma_, p. 485

Tarsal fold weak and short; thoracic fold absent or barely indicated; webbing of feet extending to base of penultimate phalanx of fourth toe; no distinct white stripe above a.n.u.s; nuptial tuberosities in breeding males consisting of small spines _H. robertsorum_, p. 481

4. Tarsal fold strong; a.n.a.l flap elongate; a.n.u.s opening at lower edge of femur; dorsum tan or brown; flanks mottled with cream and brown; venter immaculate creamy white; no a.n.a.l stripe; vocal slits present, _H. bistincta_, p. 475

Tarsal fold faint and short; a.n.a.l flap not elongate; a.n.u.s opening at middle of femur; dorsum olive-green with black reticulations; flanks greenish gray with brown or black spots; a row of white flecks above and below a.n.u.s, vocal slits absent _H. charadricola_, p. 478

ACCOUNTS OF THE SPECIES

In the following accounts complete synonymies are given for each species. In each account one specimen is described in detail; after this description the variation is discussed. In the list of specimens examined, localities are arranged alphabetically within the states, which also are given in alphabetical order. Localities given in italics are not shown on the accompanying maps (Figs. 2 and 4) due to crowding of symbols.

#Hyla bistincta# Cope

_Hyla bistincta_ Cope, Proc. Amer. Philos. Soc, 17:87, August, 1877 [Holotype.--USNM 32261 from "most probably Veracruz," Mexico; Francis Sumichrast collector]. Brocchi, etude des batraciens de l'Amerique Centrale, p. 43, 1881.

Boulenger, Catalogue Batrachia Salientia, 2nd Ed., p. 401, February 1, 1882. Sumichrast, La Naturaleza, 6:81, 1882.

Cope, Bull. U. S. Natl. Mus., 32:14, 1887; Bull. U. S. Natl.

Mus., 34:351, 1889. Gunther, Biologia Centrali-Americana, Reptilia and Batrachia, pp. 265-6, June, 1901. Diaz de Leon, Indice de los batracios que se encuentran en la Republica Mexicana, p. 17, June, 1904. Nieden, Das Tierreich, Amphibia, Anura I, p. 247, June, 1923. Kellogg, Bull. U. S. Natl. Mus., 160:163-164, March 31, 1932. Taylor, Proc. Biol. Soc.

Was.h.i.+ngton, 50:50-53, April 21, 1937; Univ. Kansas Sci.

Bull., 26:389, November 27, 1940. Taylor and Smith, Proc. U.

S. Natl. Mus., 194:87, June 7, 1948. Taylor, Univ. Kansas Publ. Mus. Nat. Hist., 1:261, August 16, 1948; Copeia, no.

4:272-273, December 15, 1949. Smith and Taylor, Univ. Kansas Sci. Bull., 33:346, March 20, 1950 [Type locality restricted to Acultzingo, Veracruz, Mexico]. Rabb and Mosimann, Occas.

Papers Mus. Zool. Univ. Michigan, 563:6-9, March 29, 1955.

Duellman, Univ. Kansas Publ. Mus. Nat. Hist., 15:47-49, December 20, 1961.

_Hyla bistincta labeculata_ Shannon, Proc. U. S. Natl. Mus., 101:470-473, figs. 92a, 93d, May 17, 1951 [Holotype.--USNM 123689 from San Lucas Camotlan, Oaxaca, Mexico; Walter S.

Miller collector]. Smith and Williams, Herpetologica, 19:23, April 11, 1963.

_Hyla bistincta bistincta_, Shannon, Proc. U. S. Natl. Mus., 101:472, May 17, 1951. Shannon and Werler, Herpetologica, 11:85, July 15, 1955. Smith and Williams, Herpetologica, 19:23, April 11, 1963.

_Diagnosis._--Maximum snout-vent length in males 54 mm.; snout in dorsal profile truncate; tarsal fold strong; inner metatarsal tubercle large, high, and elongate; outer metatarsal tubercle absent; webbing on foot extending to middle of antepenultimate phalanx of fourth toe; nuptial spines on thumb small; thoracic fold absent; a.n.a.l opening at level of lower edge of femur; dorsum brown or tan; belly cream-color; flanks creamy yellow with brown reticulations or spots; a.n.a.l stripe absent; vocal slits present.