Читать книгу A Review of the Middle American Tree Frogs of the Genus Ptychohyla - William Edward Duellman - Страница 3

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 México and northern Central America were named and described. Despite the extensive collecting by Salvin and Godman, 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 México 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 entitled "Ptychohyla as a Natural Assemblage."

Acknowledgments

I am indebted to the following persons for permitting me to examine specimens in their care: Miguel Alvarez del Toro, Museo Zoología de Tuxtla Gutierrez, México (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 institutions 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 assistance 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 México, 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 Solistahuacán, Chiapas, for a pleasant stay at their school; Jordi Juliá Z. of the Comisión del Papaloapan, Ciudad Alemán, 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 Instituto Tropical de Investigaciones Científicas, 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 México were furnished by the late Luis Macías Arellano of the Dirección 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 assign 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 analysis 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 potassium 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.

ANALYSIS OF DATA

Data that are used to arrive at a systematic arrangement of the species of Ptychohyla are analyzed and discussed below for the values inherent in the analysis. 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 analysis 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.

Table 1.—Variation in Certain Characters in the Species of Ptychohyla. (Means Are in Parentheses Below the Ranges.)

SpeciesSexNumber of specimensMaximum snout-vent lengthTibia length Snout-vent lengthTympanum EyeVomerine teethP. euthysanota euthysanota♂1738.144.4–55.0 (48.7)48.6–63.8 (56.3)4–6 (5.1)♀1553.346.5–56.6 (51.4)42.9–56.4 (51.4)6–18 (9.6)P. euthysanota macrotympanum♂538.048.8–52.0 (50.2)50.0–57.1 (54.1)0–4 (2.6)♀544.846.4–54.1 (50.2)48.7–58.9 (53.7)8–10 (9.2)P. leonhardschultzei♂1635.648.8–56.1 (51.2)48.7–61.9 (52.1)6–9 (6.5)♀341.652.3–59.5 (54.7)47.5–48.6 (48.1)7–12 (9.5)P. spinipollex♂3241.246.9–53.1 (49.0)45.0–55.2 (49.5)3–7 (4.9)♀644.646.1–50.2 (48.8)47.7–53.8 (50.4)6–10 (7.6)P. schmidtorum schmidtorum♂2532.845.3–52.4 (48.1)51.5–59.3 (54.7)5–11 (6.2)♀938.046.5–49.1 (47.7)51.3–58.3 (54.9)7–11 (8.7)P. schmidtorum chamulae♂4030.546.0–51.9 (48.2)48.2–65.6 (54.9)4–6 (4.7)♀431.848.1–52.4 (50.5)51.4–61.7 (55.7)4–9 (6.2)P. ignicolor♂1330.545.9–52.2 (49.6)37.1–47.1 (43.2)3–9 (6.1)

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 cluster of horny 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 horny excrescences on the thumbs of many species of frogs, the horny spines on the thumbs of members of the Ptychohyla euthysanota group are seasonal in development.

Fig. 1. Palmar views of right hands of (A) Ptychohyla spinipollex (KU 58054) and (B) Ptychohyla schmidtorum schmidtorum (KU 58043). × 4.

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 associated with some phase of the breeding activity.

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). × 21⁄4.

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

The dorsum in living frogs of the genus Ptychohyla is primarily yellowish or reddish brown, except in P. schmidtorum chamulae and P. ignicolor in which it is green. Usually there are some darker blotches or reticulations on the dorsum. The venter usually is white; in P. ignicolor it is yellow. The venter is spotted in all members of the Ptychohyla euthysanota group; the species, arranged from least to most spotting ventrally, are: P. euthysanota euthysanota, P. euthysanota macrotympanum, P. leonhardschultzei, and P. spinipollex. The last two species also have bold dark spots on the flanks. Ptychohyla schmidtorum lacks spots on the venter, whereas P. ignicolor has small dark flecks ventrally.

Ptychohyla euthysanota and P. schmidtorum have white stripes on the upper lips and on the flanks. All species have some form of a pale stripe above the anus and usually rather distinct white or pale stripes along the ventrolateral edges of the tarsi and forearms. There are no bright or boldly marked flash-colors (colors that are revealed only when the hind limbs are extended), except in P. ignicolor, which has bright red flash-colors in the groin and on the thighs. In life the iris varies from several different shades of bronze color to deep red in P. schmidtorum schmidtorum.

The degree of metachrosis is moderate. Usually any change of color in life consists only of change in the intensity of color. At times when the over-all coloration is darkened some markings are obscured.

Osteology

The following description of the skull, hyoid, sternum, and prepollex is based on a male specimen of P. spinipollex (KU 68632) that has been cleared and stained. The broad, flat skull (Fig. 3) has a large frontoparietal fontanelle. The ethmoid is large and has a flange laterally. The nasals are of moderate size and in broad contact with the ethmoid, but are separated from one another medially. The anterior half of the maxillary bears a thin, high flange. The anterior process of the squamosal is short and widely separated from the maxillary. The quadratojugal is a small spine-shaped element projecting anteriorly from the ventral base of the quadrate; the quadratojugal does not articulate with the maxillary.

Fig. 3. Dorsal aspect of skull of Ptychohyla spinipollex (KU 68632). Arrow indicates reduced quadratojugal. × 6.

The posteromedian part of the hyoid plate is calcified; from this plate the long bony, posterior cornua (thyrohyales) extend posterolaterally.

The omosternum is calcified, widest anteriorly, and has a convex anterior edge. The calcified xiphisternum is roughly bell-shaped having short lateral processes anteriorly and a deep notch posteriorly.

The swollen thumb is supported by a dorsoventrally flattened spine that does not extrude through the skin.

Variation.—In general, the skull varies little. Usually the quadratojugal is present only as a short element attached to the quadrate, but in one specimen of P. spinipollex the quadratojugal articulates with the maxillary and forms a complete quadratojugal-maxillary arch on each side of the skull. One specimen of P. leonhardschultzei has a complete arch on one side and an incomplete arch on the other.

Only P. spinipollex has lateral processes anteriorly on the xiphisternum; in the other species the xiphisternum is deeply bell-shaped.

Ptychohyla schmidtorum and P. ignicolor have slightly longer premaxillaries than the other species. The longer premaxillary is reflected in the larger number of teeth on the bone—9 to 11 (average 10) in four specimens of P. schmidtorum and 10 teeth in one P. ignicolor, as compared with 6 to 10 (average 7.9) in seven specimens of the other species. The number of maxillary teeth in the various species are: P. euthysanota euthysanota, 43; P. euthysanota macrotympanum, 38; P. leonhardschultzei, 38 and 40; P. spinipollex, 34 and 40; P. schmidtorum schmidtorum, 37 and 43; P. schmidtorum chamulae, 40 and 41; P. ignicolor, 43. The teeth on the premaxillary and anterior part of the maxillary are long, pointed, and terminally curved backwards. Posteriorly on the maxillary the teeth become progressively shorter and blunter.

Variation in number of vomerine teeth is shown in Table 1.

Tadpoles

Tadpoles of the genus Ptychohyla are adapted to live in mountain streams. The bodies are streamlined, and the tails are long and have low fins (Figs. 4 and 5). The mouths are large and directed ventrally. Tadpoles of the two groups of species have strikingly different mouthparts.

Fig. 4. Tadpoles of the Ptychohyla euthysanota group: (A) P. euthysanota euthysanota (KU 60042), (B) P. euthysanota macrotympanum (KU 60049), (C) P. leonhardschultzei (KU 68556), and (D) P. spinipollex (KU 60053). ×2½.

Fig. 5. Tadpoles of (A) Ptychohyla schmidtorum schmidtorum (KU 60051), (B) P. schmidtorum chamulae (KU 58199), and (C) P. ignicolor (KU 71716). × 2½.

Lips of tadpoles of the Ptychohyla euthysanota group (Fig. 6 A-D) are folded laterally; there are 4⁄6 or sometimes 4⁄7 tooth-rows. A lateral "wing" projects on either side of the upper beak. The beaks have blunt, peglike serrations. Lips of tadpoles of the Ptychohyla schmidtorum group (Fig. 6 E-G) are greatly expanded and form a funnel-shaped disc; there are 3⁄3 short tooth-rows. There is no lateral projection or "wing" on either side of the upper beak. The beaks have long, pointed serrations.

Fig. 6. Mouthparts of tadpoles of Ptychohyla: (A) P. euthysanota euthysanota (KU 60042), (B) P. euthysanota macrotympanum (KU 60049), (C) P. leonhardschultzei (KU 68556), (D) P. spinipollex (KU 60053), (E) P. schmidtorum schmidtorum (KU 60051), (F) P. schmidtorum chamulae (KU 58199), and (G) P. ignicolor (KU 71716). × 10.

Variation in certain structural details and in coloration is discussed for each species and subspecies in the systematic accounts that follow. Sizes, proportions, and numbers of tooth-rows are tabulated in Table 2.

Table 2.—Comparison of Certain Larval Characters in the Species of Ptychohyla. (Means Are in Parentheses Below the Ranges.)

SpeciesNumber of specimensMaximum lengthHead length Total lengthTooth-rowsP. euthysanota euthysanota2340.830.9–37.3 (33.5)4⁄6P. euthysanota macrotympanum1343.330.6–33.4 (32.7)4⁄6P. leonhardschultzei747.529.2–32.7 (31.1)4⁄6P. spinipollex3245.030.2–35.9 (33.0)4⁄7P. schmidtorum schmidtorum1442.528.9–31.2 (29.9)3⁄3P. schmidtorum chamulae445.026.9–29.3 (27.8)3⁄3P. ignicolor239.629.6–29.8 (29.7)3⁄3

Evidence on the pattern of development of tooth-rows indicates that the inner rows develop first. A small tadpole of P. euthysanota euthysanota has six lower rows and three fully developed upper rows and only the beginning of the first (outer) upper row. A small tadpole of P. euthysanota macrotympanum has four upper rows and five lower rows. In a small tadpole of P. leonhardschultzei the three upper and four lower tooth-rows are well developed; the first upper and fifth lower rows are beginning to develop, and the sixth lower row is absent. In small tadpoles of P. spinipollex, the sixth lower row is poorly developed, and the seventh row is absent; large individuals normally have seven lower rows. A small tadpole of P. schmidtorum chamulae has 3⁄2 tooth-rows.