Neotropical Hylid Frogs, Genus Smilisca Part 10

The deeper throat musculature is essentially the same as that described for _Phrynohyas spilomma_ by Duellman (1956), except for slight differences in the place of attachment on the hyoid.

Skin

_Structure_

The skin of _Smilisca_ is typical of that of most hylids in organization and structure. _Smilisca sila_ is distinguished from other members of the genus by the presence of small wartlike protrusions and peculiar white, pustular spots on the dorsum. The wartlike structures are composed of three or four epidermal cells, which protrude from the surface of the epidermis; the structures are covered by a slightly thickened layer of keratin. The white pustules are slightly elevated above the surrounding skin. Internally they consist of aggregations of swollen, granular, pigment-cells (perhaps lipoph.o.r.es) lying between the epidermis and the melanoph.o.r.es.

_Biochemical Variations_

Dried skins of all species of _Smilisca_ were sent to Jose M. Cei, Inst.i.tuto Nacional de Cuyo, Mendoza, Argentina, for biochemical screening by means of the chromatographic techniques described by Erspamer and Cei (1963). The species in the _baudini_ group have detectable amounts of penta-hydroxi-trypatamine, whereas only a trace is present in the other species. Furthermore, species in the _baudini_ group differ from _S. sila_ and the _sordida_ group in lacking, or having only a trace of, tryptophan-containing polypeptides. These superficial biochemical tests support the arrangement of species as ascertained by conventional taxonomic characters.

External Morphological Characters

The features of external morphology that were studied in connection with the taxonomy of the genus _Smilisca_ are discussed below.

_Size and Proportions_

The frogs of the genus _Smilisca___ are medium to large tree frogs. The three species comprising the _baudini_ group (_S. baudini_, _cyanosticta_, and _phaeota_) are notably larger than _S. puma_, _sila_, and _sordida_ (Table 6). The largest specimen that we examined is a female of _S. baudini_ having a snout-vent length of 90 mm. _Smilisca puma_ is the smallest species; the largest male has a snout-vent length of 38 mm. and the largest female, 46 mm.

Table 6.--Comparison of Sizes and Certain Proportions of the Species of Smilisca. (Means in Parentheses Below Observed Ranges; Data for Males Only.)

================+====+===========+=============+===========+ | | Snout-vent|Tibia length/| Tympanum/ | Species | N | length | snout-vent | eye | ----------------+----+-----------+-------------+-----------+ | | | | | _S. baudini_ |140 | 47.3-75.9 | 42.1-53.6 | 56.1-94.4 | | | (58.7) | (47.8) | (73.5) | | | | | | _S. cyanosticta_| 40 | 44.6-56.8 | 51.9-59.7 | 62.7-88.4 | | | (50.7) | (56.0) | (71.4) | | | | | | _S. phaeota_ | 50 | 40.8-65.5 | 50.9-60.2 | 62.7-85.5 | | | (53.9) | (55.5) | (76.6) | | | | | | _S. puma_ | 20 | 31.9-38.1 | 48.2-53.1 | 52.1-72.2 | | | (34.7) | (51.3) | (64.9) | | | | | | _S. sila_ | 33 | 31.6-44.8 | 49.7-58.1 | 47.6-58.3 | | | (37.7) | (54.8) | (53.2) | | | | | | _S. sordida_ | 55 | 31.9-44.6 | 50.5-57.1 | 46.5-57.1 | | | (37.9) | (53.4) | (49.1) | ----------------+----+-----------+-------------+-----------+

No outstanding differences in proportions exist between species, although certain proportions are sufficiently different in some species to warrant mention. _Smilisca baudini_ is a more squat and stocky frog than other members of the genus; this is reflected in the somewhat shorter hind legs (Table 6). The size of the tympanum relative to that of the eye is highly variable within samples of a given species. Even so, noticeable differences in the tympanum/eye ratio are apparent.

Members of the _baudini_ group have the largest tympani, whereas _S.

sila_ and _sordida_ have the smallest, and _S. puma_ is intermediate (Table 6).

_Shape of Snout_

Although all members of the genus have rather truncate snouts, subtle differences exist among the species (Pl. 12). _Smilisca sila_ has the shortest snout; that of _S. baudini_ is only slightly longer. The snouts of _S. cyanosticta_ and _puma_ are nearly square in lateral profile, whereas those of _S. phaeota_ and _sordida_ are slightly inclined. The shape of the snout is relatively uniform within each species and displays no noticeable s.e.xual dimorphism, except in _S. sordida_, in which there are s.e.xual differences and geographic variation (see p.

324).

_Hands and Feet_

The characters of the hands and feet are among the most taxonomically important external features in _Smilisca_. Consistent differences exist in relative lengths of the digits, size of subarticular tubercles, size and number of supernumerary tubercles, size and shape of the inner metatarsal tubercle, and amount of webbing (Pls. 4 and 5). In the _baudini_ group the series of species (_baudini-phaeota-cyanosticta_) show a progressive increase in amount of webbing in the hand and a decrease in number, and corresponding increase in size, of supernumerary tubercles. The amount of webbing in the feet of _S. baudini_ and _phaeota_ is about the same, but the webbing is slightly more extensive in _S. cyanosticta_. _Smilisca puma_ is unique in the genus in lacking webbing in the hand; furthermore, this species is distinctive in having many large subarticular tubercles on the hand and a relatively small inner metatarsal tubercle. The two stream-inhabitants, _S. sila_ and _sordida_, have shorter and stouter fingers than the other species. The webbing is most extensive in both the hands and feet of these species, which also are distinctive in having many small supernumerary tubercles on the feet.

_Ontogenetic Changes_

Minor ontogenetic changes in structure involve the shape of the snout, relative size of the eye, development of the tympanum, and amount of webbing in the hand. In recently metamorphosed young the snout is more rounded than in adults; the canthus and loreal concavity are not evident. Usually the tympanum is not differentiated in recently metamorphosed young, and the eye is proportionately large. The webbing in the feet is completely developed at metamorphosis, but young individuals have noticeably less webbing in the hand than do adults of the same species.

Coloration

Some of the most distinctive characters of the species of _Smilisca_ are color and pattern of the living frogs. Although many chromatic features are lost or subdued in preserved specimens, the patterns usually persist.

_Metachrosis_

Change in color, well known in frogs, is common in hylids, especially in species having green dorsal surfaces (_Phyllomedusa_ is a notable exception). The non-green _Smilisca_ (_puma_, _sila_, and _sordida_) changes color, but this mostly is a change in intensity of color. In these species the markings usually are most distinct at night; frequently by day the frogs become pallid. The most striking examples of metachrosis in _Smilisca_ are found in the _baudini_ group, in which the dorsal ground-color changes from green to tan; correlated with the change in ground-color may be a corresponding change in the dorsal markings, but the dorsal markings may change to the opposite color.

Chromosomes

Chromosomes of all six species of _Smilisca_ were studied by means of the propriono-orcein squash technique described by Duellman and Cole (1965). Karyotype a.n.a.lysis was attempted for several species by means of intraperitoneal injections of colchicine, which affected the mitotic cells as desired, but the testes examined contained too few mitotic cells to allow accurate determination of karyotypes.

Haploid (_n_) chromosome numbers were determined from cells in diakinesis, metaphase I, and metaphase II of meiosis. Diploid (2_n_) chromosome numbers were determined from cells in late prophase and metaphase of mitosis. Chromosome counts from as few as 23 meiotic cells of _S. phaeota_ and as many as 80 cells of _S. sordida_ reveal a constant haploid (_n_) number of 12; counts of chromosomes in one to five mitotic cells in all species, except _S. sila_, reveal that the diploid (2_n_) number is 24.

NATURAL HISTORY

Breeding

Like most hylid frogs _Smilisca_ is most readily collected and observed when individuals congregate for breeding.

_Time of Breeding_

_Smilisca_ breeds primarily in quiet water and reaches its height of breeding activity at times of plentiful rainfall,--usually from May through October. Through most of its range _Smilisca baudini_ breeds in those months, but in some places where abundant rain falls in other seasons, the species breeds at those times. For example, in southern El Peten and northern Alta Verapaz, Guatemala, _Smilisca baudini_ has been found breeding in February and March. The other pond-breeding species (_S. cyanosticta_, _phaeota_, and _puma_) live in regions lacking a prolonged dry season, and possibly they breed throughout the year, but breeding activity seems to be greatest in the rainiest months.

The two stream-breeding species (_S. sila_ and _sordida_) breed in the dry season when the streams are low and clear, princ.i.p.ally in December through April. At high elevations the species sometimes breed in the rainy season; also, individuals sometimes breed in the short dry season (summer canicula) in July and August.

At several localities species have been found breeding at different times of the year: _S. baudini_ in March and July at Chinaja, Guatemala; _S. phaeota_ in April and August at Palmar Sur, Costa Rica; _S. puma_ in February and July at Puerto Viejo, Costa Rica; and _S. sila_ in February, April, and August at El Volcan, Panama. These observations indicate only that the population breeds at more than one time in the year, but do not provide any evidence on the breeding cycles of the individual frogs. This is one important aspect of the natural history of _Smilisca_ for which we lack data.

_Breeding Sites_

All members of the genus _Smilisca_ presumably deposit their eggs in water.

_Smilisca baudini_ usually breeds in temporary rain pools; often these are nothing more than shallow, muddy puddles. In other instances the sites are extensive ditches or large flooded areas (Pl. 8, Fig. 1). This species is an opportunistic breeder, and males gather at any of a wide variety of suitable breeding sites that are formed by torrential rains in the early part of the rainy season. _Smilisca baudini_ nearly always breeds in open pools having bare earthen edges. Frequently congregations of _S. baudini_ are found at such small pools, but are absent from nearby large ponds surrounded by vegetation.

Little is known of the breeding habits of _S. cyanosticta_, which inhabits humid forests on foothills and lowlands. Apparently its breeding sites are not unlike those of _S. phaeota_, which usually are pools surrounded by vegetation (Pl. 8, Fig. 2), although sometimes males of _S. cyanosticta_ call from open muddy puddles. In uplands, where standing water is uncommon, this species breeds in quiet pools in streams.

_Smilisca puma_ breeds in gra.s.s-choked ponds and marshes, where the males call from bases of dense clumps of gra.s.s in the water (Pl. 9, Fig.

1).

_Smilisca sila_ and _S. sordida_ differ noticeably from other species in the genus by breeding exclusively in streams, where males usually call from rocks or gravel bars in or at the edges of streams (Pl. 9, Fig. 2); sometimes individuals perch on bushes overhanging streams. In the streams, or parts of streams, utilized by these frogs the water is clear, shallow, and has a slow gradient; occasional males have been found calling along cascading mountain streams.

Breeding choruses composed of ten or more species of frogs are not uncommon in Middle America, but _Smilisca_ usually breeds alone or with one or two other species and at the most five others. This tendency towards solitary breeding possibly is the result of selection of breeding sites that are unsuitable to many other species of frogs.

Nevertheless, many other species of frogs have been found at the breeding sites with the various species of _Smilisca_; these breeding a.s.sociates (Table 7) are most numerous for _S. baudini_, which has a broad geographic range, including a variety of habitats.

_Breeding Behavior_

_Calling sites._--All species of _Smilisca_ usually call from the ground, including rocks and gravel bars; some individuals sit in shallow water near the edge of the pool or stream. Sometimes males of _S.

baudini_, _sila_, and _sordida_ call from low bushes or trees near the breeding site. One _S. baudini_ was observed calling while it was floating on the surface of a pond. _Smilisca cyanosticta_, _phaeota_, and _puma_ call from secluded places at the edge of the water or in the water, whereas _S. baudini_, _sila_ and _sordida_ call from open situations.