A Review of the Middle American Tree Frogs of the Genus Ptychohyla.

by William E. Duellman.

INTRODUCTION

Probably no ecological group of hylid frogs (some _Hyla_ plus _Plectrohyla_ and _Ptychohyla_) in Middle America is so poorly known as those species that live in the cloud forests on steep mountain slopes and breed in cascading mountain streams. During the last half of the nineteenth century most of the species of hylids living in the lowlands of southern Mexico and northern Central America were named and described. Despite the extensive collecting by Salvin and G.o.dman, Nelson and Goldman, and the various expeditions of the _Mission Scientifique_, no members of the genus _Ptychohyla_ were obtained until 1927, when in the mountains of El Salvador Ruben A. Stirton found a small tree frog that subsequently was described and named _Hyla euthysanota_ by Kellogg (1928). Until recently frogs of this genus were known from few specimens and in the literature by nearly as many names.

Although I first collected _Ptychohyla_ in 1956, it was not until 1960 that special efforts were made to obtain specimens of this genus. The summer of 1960 was spent in southern Mexico and Guatemala, where every accessible stream in the cloud forests was searched for tree frogs, especially _Ptychohyla_ and _Plectrohyla_. Similar, but less extensive, investigations were carried out in 1961 and 1962. The result of this field work is a rather large collection of _Ptychohyla_ representing all of the known species, plus tape recordings of the breeding calls and tadpoles of all of the species.

Previously, I have discussed the nomenclature of one of the species (Duellman, 1960) and have described two new species (Duellman, 1961).

In the latter paper I made reference to a future account (this one) that would deal with the systematics and biology of the entire genus.

Although I have series of specimens, tadpoles, osteological preparations, and recordings of breeding calls, thereby having a wide array of data at my disposal, much still remains to be learned about these frogs, especially about various aspects of their life histories.

Even the validity of the genus is open to question; this problem is discussed at length in the section beyond ent.i.tled "_Ptychohyla_ as a Natural a.s.semblage."

Acknowledgments

I am indebted to the following persons for permitting me to examine specimens in their care: Miguel Alvarez del Toro, Museo Zoologia de Tuxtla Gutierrez, Mexico (MZTG); Charles M. Bogert and Richard G.

Zweifel, American Museum of Natural History (AMNH); Doris M. Cochran, United States National Museum (USNM); Norman Hartweg and Charles F.

Walker, University of Michigan Museum of Zoology (UMMZ); Robert F.

Inger, Chicago Natural History Museum (CNHM); Hobart M. Smith, University of Illinois Museum of Natural History (UIMNH); Heinz Wermuth, Zoologisches Museum Berlin (ZMB); and Ernest E. Williams, Museum of Comparative Zoology (MCZ). The abbreviations following names of inst.i.tutions will be used throughout the text; the Museum of Natural History at the University of Kansas is abbreviated KU.

Throughout my work on these frogs I have profited from discussions with L. C. Stuart, who has made many valuable suggestions and with his characteristic generosity has placed at my disposal his extensive collections of tadpoles from Guatemala. For his aid I am indeed grateful. I am grateful to Thomas E. Moore for tapes of breeding calls of two species.

My own field work was made more enjoyable and profitable through the a.s.sistance of Dale L. Hoyt, Craig E. Nelson, Jerome B. Tulecke, and John Wellman, all of whom spent many hours in often unsuccessful attempts to collect specimens and record breeding calls of _Ptychohyla_. I am indebted to many residents of Mexico, Guatemala, and El Salvador for permission to work on their land and for providing shelter, food, and guides. I am especially grateful to Mr. and Mrs.

Horatio Kelly of "Colegio Linda Vista" at Pueblo Nuevo Solistahuacan, Chiapas, for a pleasant stay at their school; Jordi Julia Z. of the Comision del Papaloapan, Ciudad Aleman, Veracruz, for arranging for field work in northern Oaxaca in 1959; Walter Hannstein and Lothar Menzel for the use of facilities at Finca La Paz, Guatemala, in 1960; Alan Hempstead for the use of facilities at Finca Los Alpes, Guatemala in 1960 and 1961; and Julio Aguirre C. of the Inst.i.tuto Tropical de Investigaciones Cientificas, San Salvador, El Salvador, for providing comfortable working quarters and transportation and guides to the mountains in northern El Salvador. Without the cheerful efforts of Jorge A. Ibarra, Director of the Museo Nacional de Historia Natural in Guatemala, my field work would have been greatly restricted during politically precarious times in that country. Permits to collect in Mexico were furnished by the late Luis Macias Arellano of the Direccion General de Caza. Each of these individuals has my profound thanks for his indispensable aid.

Field work on hylid frogs in Middle America has been supported by the National Science Foundation, Grant NSF-G9827, and this is the 9th publication on the results of study of the material from America.

Materials and Methods

During the course of this study I have examined 247 frogs that I a.s.sign to the genus _Ptychohyla_, plus 40 lots of tadpoles and 12 skeletal preparations. Furthermore, I have examined all of the type specimens. I have studied each of the species and subspecies in the field and have examined from seven (_P. euthysanota macrotympanum_) to 33 (_P. spinipollex_) living individuals of each species.

Measurements given in the a.n.a.lysis of data and in the descriptions of the species are those described by Duellman (1956). In the descriptions of living colors the capitalized names are from Ridgway (1912). All interpretations of osteological characters are based on specimens cleared in pota.s.sium hydroxide and stained with alizarin red.

Recordings of the breeding calls were made with a Magnemite Portable Tape-recorder; audiospectrographs were made on a vibralyzer (Kay Electric Company) using normal pattern and wide bandwidth.

a.n.a.lYSIS OF DATA

Data that are used to arrive at a systematic arrangement of the species of _Ptychohyla_ are a.n.a.lyzed and discussed below for the values inherent in the a.n.a.lysis. These data are of some value also in the recognition of species and subspecies but if employed for that purpose the data must be used in combination with the keys and the diagnoses of the individual species and subspecies.

External Morphology

Each of the external morphological characters used in the systematic treatment of _Ptychohyla_, as well as the nature of the tongue, is discussed below.

SIZE AND PROPORTIONS.--Comparisons of size and certain proportions are given in Table 1. Frogs of this genus are small; the largest specimen examined is a female of _P. euthysanota euthysanota_ having a snout-vent length of 53.3 mm. The species comprising the _Ptychohyla schmidtorum_ group are smaller; the largest specimen examined is a female of _P. schmidtorum schmidtorum_ having a snout-vent length of 38.0 mm. An a.n.a.lysis of the various measurements and proportions shows few constant differences. _Ptychohyla ignicolor_ differs from all of the other species in having the head slightly wider than long and the tympanum noticeably less than half the size of eye. _Ptychohyla spinipollex_ has a relatively narrow interorbital distance, approximately equal to the width of the eyelid, whereas in all of the other species that distance is much more than the width of the eyelid.

SNOUT.--All species have a blunt snout. In _P. leonhardschultzei_ and _P. ignicolor_ the snout is nearly square in lateral profile; in _P.

schmidtorum_ the snout is slightly rounded above and below, and in the other species it is rounded above. _Ptychohyla leonhardschultzei_ and _P. spinipollex_ have a vertical fleshy rostral keel on the snout; in these species, because of this keel, the snout in dorsal profile is pointed. The nostrils are slightly protuberant in all species, and in _P. schmidtorum_ the internarial region is slightly depressed.

HAND.--The species in the _Ptychohyla euthysanota_ group have a vestige of web between the first and second fingers; the other fingers are about one-third webbed. Breeding males have a cl.u.s.ter of h.o.r.n.y nuptial spines on the thumb. The spines are largest in _P. spinipollex_ (Fig. 1) and vary in number from 35 to 66 (average 47.4) on each thumb.

In the other species of the _Ptychohyla euthysanota_ group the spines are smaller and usually more numerous; the numbers of spines on each thumb (means in parentheses) in members of this group are: _P.

euthysanota euthysanota_, 44-143 (83.8); _P. euthysanota macrotympanum_, 40-110 (63.0); _P. leonhardschultzei_, 24-80 (54.7).

The species in the _Ptychohyla schmidtorum_ group have no web between the first and second fingers and only a vestige of web between the other fingers. Furthermore, these species lack nuptial spines in breeding males. Like the usual h.o.r.n.y excrescences on the thumbs of many species of frogs, the h.o.r.n.y spines on the thumbs of members of the _Ptychohyla euthysanota_ group are seasonal in development.

TABLE 1.--VARIATION IN CERTAIN CHARACTERS IN THE SPECIES OF PTYCHOHYLA.

(MEANS ARE IN PARENTHESES BELOW THE RANGES.)

Key to Table Columns

A) Number of specimens B) Maximum snout-vent length C) Tibia length/Snout-vent length D) Tympanum/Eye E) Vomerine teeth

==================+========+======+=======+=========+=========+======= Species | s.e.x | A | B | C | D | E ------------------+--------+------+-----------------+----------------- | | | | | | _P. euthysanota | [Male] | 17 | 38.1 |44.4-55.0|48.6-63.8| 4-6 euthysanota_ | | | | (48.7) | (56.3) | (5.1) | | | | | | |[Female]| 15 | 53.3 |46.5-56.6|42.9-56.4| 6-18 | | | | (51.4) | (51.4) | (9.6) | | | | | | _P. euthysanota | [Male] | 5 | 38.0 |48.8-52.0|50.0-57.1| 0-4 macrotympanum_| | | | (50.2) | (54.1) | (2.6) | | | | | | |[Female]| 5 | 44.8 |46.4-54.1|48.7-58.9| 8-10 | | | | (50.2) | (53.7) | (9.2) | | | | | | _P. leonhard | [Male] | 16 | 35.6 |48.8-56.1|48.7-61.9| 6-9 schultzei_ | | | | (51.2) | (52.1) | (6.5) | | | | | | |[Female]| 3 | 41.6 |52.3-59.5|47.5-48.6| 7-12 | | | | (54.7) | (48.1) | (9.5) | | | | | | _P. spinipollex_ | [Male] | 32 | 41.2 |46.9-53.1|45.0-55.2| 3-7 | | | | (49.0) | (49.5) | (4.9) | | | | | | |[Female]| 6 | 44.6 |46.1-50.2|47.7-53.8| 6-10 | | | | (48.8) | (50.4) | (7.6) | | | | | | _P. schmidtorum | [Male] | 25 | 32.8 |45.3-52.4|51.5-59.3| 5-11 schmidtorum_ | | | | (48.1) | (54.7) | (6.2) | | | | | | |[Female]| 9 | 38.0 |46.5-49.1|51.3-58.3| 7-11 | | | | (47.7) | (54.9) | (8.7) | | | | | | _P. schmidtorum | [Male] | 40 | 30.5 |46.0-51.9|48.2-65.6| 4-6 chamulae_ | | | | (48.2) | (54.9) | (4.7) | | | | | | |[Female]| 4 | 31.8 |48.1-52.4|51.4-61.7| 4-9 | | | | (50.5) | (55.7) | (6.2) | | | | | | _P. ignicolor_ | [Male] | 13 | 30.5 |45.9-52.2|37.1-47.1| 3-9 | | | | (49.6) | (43.2) | (6.1) ------------------+--------+------+-------+---------+---------+-------

[Ill.u.s.tration: FIG. 1. Palmar views of right hands of (A) _Ptychohyla spinipollex_ (KU 58054) and (B) _Ptychohyla schmidtorum schmidtorum_ (KU 58043).]

Many workers have used the presence of a bifid subarticular tubercle beneath the fourth finger as a diagnostic character of certain species of hylids. Examination of the subarticular tubercles in _Ptychohyla_ reveals considerable intraspecific variation. Bifid tubercles beneath the fourth finger are found in all species except _P. ignicolor_, which is known from only two specimens. In _P. euthysanota euthysanota_ nearly 60 per cent and in _P. schmidtorum schmidtorum_ about 90 per cent of the specimens have a bifid tubercle beneath the fourth finger on one or both hands. All specimens of _P.

leonhardschultzei_ have either a bifid or double tubercle beneath the fourth finger, and some have a bifid distal tubercle beneath the third finger.

FEET.--Members of the _Ptychohyla euthysanota_ group have a weak tarsal fold, whereas in the species comprising the _Ptychohyla schmidtorum_ group the tarsal fold is absent. Webbing on the foot extends to the discs of the third and fifth toes and to the base of the penultimate phalanx of the fourth toe, except in _P. ignicolor_, which has less webbing.

VENTROLATERAL GLANDS.--Breeding males develop thickened, pigmented glandular areas on the sides of the body. In living specimens of _P.

schmidtorum_ and _P. ignicolor_ the glands are not readily visible, but in preservative they show as distinctive orange-colored areas.

These glands are most distinct in _P. euthysanota_; in many specimens of this species the glands are elevated above the surrounding skin.

The extent of the glands is variable (Fig. 2); probably this variability is due to different degrees of development in individual frogs rather than to interspecific differences. All _Ptychohyla ignicolor_ and some _P. schmidtorum chamulae_ have a small, round glandular area on the chin; to my knowledge this does not occur in the other species. Superficial examination of microscopic preparations of the glands reveals no histological differences between species. The glands occupy most of the thickened area and have narrow ducts leading to the exterior. Detailed studies of the histology will be reported elsewhere. Since the glands are developed only in breeding males, it is surmised that the glands are a.s.sociated with some phase of the breeding activity.

[Ill.u.s.tration: FIG. 2. Normal extent of ventrolateral glands in (A) _Ptychohyla euthysanota euthysanota_ (KU 58008), (B) _Ptychohyla schmidtorum schmidtorum_ (KU 58037), and (C) _Ptychohyla ignicolor_ (UMMZ 119603).]

TONGUE.--The shape of the tongue varies intraspecifically. Usually the tongue is ovoid; in some specimens it is barely notched posteriorly, whereas in others it is deeply notched, making the tongue cordiform.

Deeply notched cordiform tongues are found in _P. leonhardschultzei_ and _P. schmidtorum_; with the exception of these two species, some individuals of all species have emarginate tongues. Some individuals of all species have tongues that are shallowly notched posteriorly.

Color and Pattern