Middle American Frogs of the Hyla microcephala Group Part 1

Middle American Frogs of the Hyla microcephala Group.

by William E. Duellman and M. J. Fouquette.

INTRODUCTION

The small yellow tree frogs, _Hyla microcephala_ and its relatives, are among the most frequently heard and commonly collected frogs in the lowlands of southern Mexico and Central America. The similarities in size, proportions, and coloration of the different species have resulted not so much in a multiplicity of specific names, but in differences of opinion on the application of existing names to the various taxa. For example, the populations on the Atlantic lowlands have been known by three names, two of which have been applied to other taxa. Much of the confusion has been the result of previous workers' unfamiliarity with the animals in life and unawareness of the intraspecific geographic variation in the most widespread species.

Independently we undertook studies of these frogs in the field. The second author worked on the interspecific relationships and isolating mechanisms in Panama (Fouquette, 1960b) and later studied the species in southern Mexico. As part of his survey of the hylids of Middle America, the first author acc.u.mulated field and laboratory data on the frogs throughout their ranges in Mexico and Central America. The purpose of this report is to present our findings on the four species of Middle American frogs that we place in the _Hyla microcephala_ group. In addition to conventional taxonomic characters, we have utilized the features of the cranial osteology and have relied heavily on the data obtained from an a.n.a.lysis of the mating calls.

Furthermore, we have included ecological and distributional data in our synthesis of interspecific relationships.

ACKNOWLEDGMENTS

Examination of specimens was made possible by the provision of working s.p.a.ce at various inst.i.tutions or through the loan of specimens. For their generosity in this manner we are grateful to Richard J. Baldauf, Charles M. Bogert, James E. Bohlke, Doris M. Cochran, Robert F. Inger, John M. Legler, Alan E. Leviton, Gerald Raun, Jay M. Savage, Hobart M.

Smith, Robert C. Stebbins, Wilmer W. Tanner, Charles F. Walker, Ernest E. Williams, and Richard G. Zweifel.

Duellman is especially grateful to Charles W. Myers, Linda Trueb, Jerome B. Tulecke, and John Wellman for their a.s.sistance in the field and to Linda Trueb for her work on the cranial osteology that is incorporated in this report. Fouquette is indebted to H. Morgan Smith and A. C. Collins for a.s.sistance in the field, to A. J. Delahoussaye for a.s.sistance in the laboratory, and to W. Frank Blair for use of the facilities of the sound laboratory at the University of Texas and for much help in the early stages of this study.

The research reported herein was accomplished mainly through support by the National Science Foundation (grants NSF G-9827 and GB-1441 to Duellman and GB-599 to Fouquette). The latter's field work in Mexico was a.s.sisted in part by NSF Grant G-4956 to W. Frank Blair. Some of the field studies carried out in Panama by Duellman were supported by a grant from the National Inst.i.tutes of Health (NIH GM-12020).

We are grateful to many persons, too numerous to mention, who in various ways aided our field work in Middle America. We are especially indebted to Dr. Rodolfo Hernandez Corzo and the late Ing. Luis Macias Arellano of the Direccion General de la Fauna Silvestre of the Mexican government for providing permits to collect in Mexico.

Materials and Methods

For this report, data has been obtained from 2829 preserved frogs, 42 skeletal preparations, 8 lots of tadpoles and young, and 4 lots of eggs. Much of the material was collected in our independent field work, which has extended over a period of 11 years.

Measurements were taken in the manner described by Duellman (1956).

Osteological data were obtained from specimens that were cleared in pota.s.sium hydroxide, stained with alizarin red, and stored in glycerine. Recordings were made by means of Magnemite portable tape recorders (Amplifier Corp. America). The calls recorded by Fouquette were a.n.a.lyzed on a Sonagraph (Kay Electric Co.) at the University of Texas; those recorded by Duellman were a.n.a.lyzed mainly on a Vibralyzer (Kay Electric Co.) at the University of Kansas and in part on a Sonagraph at the University of Southwestern Louisiana. Sample calls were a.n.a.lyzed on all three instruments; the slight differences in results were found to be less than the error in measurement, so the data from all sources were combined without correction. The techniques and terminology of the calls are those defined by Fouquette (1960a, 1960b).

In the accounts of the species we have attempted to give a complete synonymy. At the end of each species account the localities from which specimens were examined are listed alphabetically within each state, province, or department, which in turn are listed alphabetically within each country. The countries are arranged from north to south.

Localities preceded by an asterisk (*) are not plotted on the accompanying maps due to the crowding of symbols that would have resulted. Abbreviations for museum specimens are listed below:

AMNH --American Museum of Natural History ANSP --Academy of Natural Sciences of Philadelphia BMNH --British Museum (Natural History) BYU --Brigham Young University CAS --California Academy of Sciences FMNH --Field Museum of Natural History KU --University of Kansas Museum of Natural History MCZ --Museum of Comparative Zoology MVZ --Museum of Vertebrate Zoology SU --Stanford University UIMNH--University of Illinois Museum of Natural History UMMZ --University of Michigan Museum of Zoology USC --University of Southern California USNM --United States National Museum UU --University of Utah TCWC --Texas Cooperative Wildlife Collection TNHM --Texas Natural History Museum

HYLA MICROCEPHALA GROUP

_Definition._--Small hylids attaining a maximum snout-vent length of 27 mm. in males and 32 mm. in females; dorsum yellowish tan with brown markings; thighs uniformly yellow, vocal sac in breeding males yellow; snout truncate in lateral profile; tympanum distinct, usually slightly smaller than one-half diameter of eye; vocal sac single, median, subgular; fingers about one-third webbed; toes webbed nearly to bases of discs, except only to middle of antepenultimate or base of penultimate phalanx of fourth toe; tarsal fold weak; inner metatarsal tubercle low, flat, elliptical; axillary membrane present; pupil horizontally elliptical; palpebral membrane unmarked; cranial elements reduced in ossification; sphenethmoid small, short; frontoparietal fontanelle large; tegmen tympani not extensive; quadratojugal greatly reduced; anterior arm of squamosal extending only about one-fourth distance to maxillary; posterior arm of squamosal not having bony connection with prootic; nasals lacking maxillary processes; medial ramus of pterygoid not having bony attachment to prootic; maxillary, premaxilary, and prevomerine teeth present; palatine and parasphenoid teeth absent; Mentomeckelians ossified; tadpoles having xiphicercal tails with deep caudal fins and terminal mouth lacking teeth; mating call consisting of one primary note followed by a series of shorter secondary notes; haploid number of chromosomes, 15 (known only in _H.

microcephala_ and _H. phlebodes_.)

_Content._--As recognized here the _Hyla microcephala_ group contains four species, one having two subspecies. An alphabetical list of the specific and subspecific names that we consider to be applicable to the _Hyla microcephala_ group are listed below.

Names Proposed Valid Names

_Hyla cherrei_ Cope, 1894 ? = _H. m. microcephala_ _Hyla microcephala_ Cope, 1886 = _H. m. microcephala_ _Hyla microcephala_ Boulenger, 1898 (_nec_ Cope, 1886) = _H. microcephala underwoodi_ _Hyla microcephala martini_ Smith, 1951 = _H. microcephala underwoodi_ _Hyla microcephala sartori_ Smith, 1951 = _H. sartori_ _Hyla phlebodes_ Stejneger, 1906 = _H. phlebodes_ _Hyla robertmertensi_ Taylor, 1937 = _H. robertmertensi_ _Hyla underwoodi_ Boulenger, 1899 = _H. microcephala underwoodi_

_Discussion._--The color pattern is the most useful character in distinguishing the species of the _Hyla microcephala_ group from one another. Except in _Hyla microcephala_, little geographic variation in color pattern is noticeable. The features of color pattern that are helpful in identifying the species are: 1) presence or absence of lateral dark brown stripe; 2) longitudinal extent and width of lateral stripe, if present; 3) presence or absence of a narrow white line just dorsal to the lateral dark stripe; 4) presence or absence of an interorbital dark mark; 5) the arrangement of dark markings on the back, either as longitudinal lines or series of dashes, or in the form of various kinds of transverse markings; 6) presence of dark flecks, longitudinal line, or transverse marks on shanks.

Few consistent differences in measurements and proportions exist among the species (Table 1). The most obvious morphological difference is that the head is noticeably narrower in _H. robertmertensi_ than in the other species. _Hyla phlebodes_ is the smallest species; adult males attain snout-vent lengths of only 23.6 mm. The body is slender in _H. microcephala_ and _robertmertensi_, slightly wider in _phlebodes_, and noticeably broader in _sartori_.

_Distribution._--The composite range of the Middle American frogs of the _Hyla microcephala_ group includes the lowlands of southern Mexico and Central America, in some places to elevations of 1200 meters, southeastward from southern Jalisco and southern Veracruz, excluding arid regions (northern Yucatan Peninsula, Balsas-Tepalcatepec Basin, Plains of Tehuantepec, Grijalva Valley, Salama Basin, and upper Motagua Valley) to the Pacific lowlands and the Cauca and Magdalena valleys in Colombia.

Key to Species and Subspecies

1. Lateral dark stripe, bordered above by narrow white line, extending from snout at least to sacral region 2

Lateral dark stripe, if present, not extending posteriorly to sacral region and not bordered above by narrow white line 4

2. Lateral dark stripe continuous to groin; dark flecks or longitudinal line on shanks; interorbital dark bar absent; dorsal pattern usually consisting of pair of longitudinal dark lines or series of dashes 3

Lateral dark stripe usually extending only to sacral region; dark transverse bars on shanks; interorbital bar usually present; dorsal pattern usually consisting of interconnecting dark lines, sometimes forming transverse marks _H. microcephala underwoodi_

3. Lateral dark stripe narrow, covering only upper edge of tympanum; dorsal longitudinal stripes continuous, extending to vent _H. microcephala microcephala_

Lateral dark stripe wide, encompa.s.sing entire tympanum; dorsal markings consisting of longitudinal series of flecks or dashes, or of two lines, usually not extending to vent _H. robertmertensi_

4. Lateral dark stripe indistinct, present only above tympanum and insertion of arm; dorsal markings consisting of narrow lines and dashes, sometimes interconnected; transverse bars on shanks narrow relative to inters.p.a.ces _H. phlebodes_

Lateral dark stripe absent; dorsal markings consisting of two broad chevron-shaped marks; transverse bars on shanks wide relative to inters.p.a.ces _H. sartori_

ACCOUNTS OF SPECIES AND SUBSPECIES

_Hyla microcephala_ Cope

_Diagnosis._--Lateral dark stripe narrow, covering only upper edge of tympanum, bordered above by narrow white stripe; dorsal pattern consisting of pair of longitudinal brown lines and no interorbital bar (eastern populations), or of irregular dark markings forming an X- or )(-shaped mark in scapular region and an interorbital bar (western populations).

_Content._--The populations inhabiting the Pacific lowlands of southeastern Costa Rica eastward to Colombia are recognized herein as _Hyla microcephala microcephala_ Cope; the populations in western Costa Rica northward to Mexico are a.s.signed to _Hyla microcephala underwoodi_ Boulenger.

_Distribution._--Southern Veracruz and northern Oaxaca southeastward through the Atlantic lowlands of Central America to north-central Nicaragua, thence southeastward on the Pacific lowlands to eastern Panama, and thence into the Cauca and Magdalena valleys (Caribbean drainage) of Colombia (Fig. 1).

[Ill.u.s.tration: Fig. 1. Map showing locality records for _Hyla microcephala_.]