Part 17

The genus is readily divided into two species-groups on morphological characters; this division is supported by the breeding calls. In the species of the baudini group the calls are unmodulated and lack secondary notes. In the sordida group the calls either have secondary notes or are modulated.

Smilisca baudini occurs sympatrically with S. cyanosticta and S. phaeota; where they occur together, both species sometimes breed in like places at the same time. We are not aware of these species breeding synchronously at exactly the same site, although S. baudini and S. cyanosticta were calling on the same nights and less than 100 meters apart in Oaxaca in June, 1964. Regardless of their respective breeding habits, sympatric species have calls that differ notably. Except for the higher fundamental and dominant frequencies, the calls of S. cyanosticta and S. phaeota closely resemble one another, but the calls of both species differ markedly from that of S. baudini. The geographic ranges of S. cyanosticta and S. phaeota are widely separated.

The calls of the allopatric species S. puma and S. sila are not greatly different. Smilisca sordida has a distinctive call and occurs sympatrically with S. puma and S. sila. In the streams in southern Costa Rica S. sordida and S. sila breed synchronously, but the high-pitched modulated call of the former is notably different from the lower, unmodulated call of S. sila.

The data indicate that the calls of related sympatric species differ more than the calls of related allopatric species. We postulate that these differences evolved to support the reproductive isolation of the sympatric species. The data are insufficient to determine geographic variation in the calls and to determine if differences in the calls are enhanced in areas of sympatry as compared with the allopatric parts of the ranges.

Other calls.--As stated previously, there is no direct evidence of territoriality in Smilisca; we have heard no calls that can be definitely identified as territorial. Single notes of S. baudini, phaeota, and sila have been heard by day, just prior to rains, or during, or immediately after rains. Such calls can be interpreted as "rain calls," which are well known in Hyla eximia and Hyla squirella. Distress calls are known in several species of Rana and in Leptodactylus pentadactylus; such calls result from the rapid expulsion of air over the vocal cords and with the mouth open. Distress calls have been heard from S. baudini. At Charapendo, Michoacan, Mexico, a male that had one hind limb engulfed by a Leptodeira maculata emitted several long, high-pitched cries. A clasping pair of S. baudini was found in a bush at the edge of a marshy stream 2 kilometers northeast of Las Canas, Guanacaste Province, Costa Rica. When the pair was grasped, the female emitted a distress call.

Eggs

Eggs of S. baudini, cyanosticta, and phaeota have been found in the field, and eggs of S. sila have been observed in the laboratory. The eggs of S. puma and sordida are unknown. Insofar as known, Smilisca baudini is unique in the genus in depositing the eggs in a surface film. Each egg is encased in a vitelline membrane, but individual outer envelopes are lacking. The eggs are small; the diameter of recently-deposited eggs is about 1.3 mm. and that of the vitelline membrane is about 1.5 mm. The eggs of S. cyanosticta and phaeota are deposited in clumps, and the eggs are larger than those of S. baudini. Diameters of eggs of S. cyanosticta are about 2.3 mm., and those of the outer envelopes are about 4.0 mm. Artificially fertilized eggs of S. sila raised in the laboratory have diameters of about 2.4 mm.; the diameter of the outer envelopes is about 4.9 mm.

In order to determine the reproductive potential of the six species, ovulated eggs were removed from females and counted. The numbers of eggs recorded are: 3 S. baudini--2620, 2940, 3320; 1 S. cyanosticta--910; 3 S. phaeota--1665, 1870, 2010; 1 S. puma--518; 3 S. sila--369, 390, 473; 3 S. sordida--524, 702, 856. These limited data indicate that the large species (S. baudini, cyanosticta, and phaeota) have more eggs than do the smaller species. The stream-breeding species (S. sila and sordida) have relatively few eggs by comparison with the pond-breeders. Possibly this is a function of size of eggs rather than a correlation with the site of egg-deposition.

Tadpoles

The acquisition of tadpoles of all of the species of Smilisca has made possible the use of larval characters in erecting a classification and in estimating the phylogenetic relations of the several species. Furthermore, developmental series of tadpoles of four species allow a comparison of the growth and development in these species. Throughout the discussion of tadpoles we have referred to the various developmental stages by the Stage Numbers proposed by Gosner (1960).

General Structure

Tadpoles of the genus Smilisca are of a generalized hylid type, having 2/3 tooth-rows, unspecialized beaks, mouth partly or completely bordered by papillae, lateral fold present in the lips, spiracle sinistral, anal tube dextral, and caudal musculature extending nearly to tip of caudal fin. Although minor differences exist in coloration, proportions, and mouthparts, no great modifications of the basic structure are present.

Comparison of Species

The larval characters of the species of Smilisca are compared below and illustrated in Figures 11-15.

Shape and Proportions.--The bodies of S. baudini, cyanosticta, phaeota, and puma are rounded and about as wide as deep; the eyes are moderately large and directed dorsolaterally, and the nostrils are about midway between the bluntly rounded snout and the eyes. The mouths are medium-sized and directed anteroventrally. The bodies of tadpoles of S. sila and sordida are slightly compressed dorso-ventrally. The snout is moderately long and sloping; the eyes are larger and directed more dorsally than in the other species, and the nostrils are closer to the eyes than the snout. The mouths are moderately large and directed ventrally.

The tail is about half again as long as the body in S. baudini, cyanosticta, phaeota, and puma; in these species the caudal musculature is moderately heavy, and the caudal fins are deep. The caudal musculature is upturned distally in S. baudini and phaeota, and the dorsal fin extends anteriorly onto the body in these two species and in S. puma. The tail is about twice as long as the body in S. sila and sordida. In both species the caudal fins are shallow in comparison with the depth of the caudal musculature, especially in S. sordida (Fig. 14); in neither species does the dorsal fin extend anteriorly onto the body.

Mouthparts.--The mouth of S. sordida is completely bordered by two rows of papillae, whereas in the other species the median part of the upper lip is devoid of papillae. Smilisca baudini and puma have two rows of papillae; S. sila has one complete row (except medially on the upper lip) and one incomplete row, and S. cyanosticta and phaeota have only one row (Fig. 15). All species have numerous papillae in the lateral fold; the fewest lateral papillae are found in S. cyanosticta and phaeota. Although all species have two rows of teeth in the upper jaw and three rows in the lower jaw, specific differences in the nature of the rows exist between certain species. The second upper tooth-row is narrowly interrupted medially in S. sila and sordida and broadly interrupted in the other species. The first upper row is strongly arched in S. puma, moderately arched in S. baudini and sila, and weakly arched in the other species. In all species the third lower tooth-row is the shortest, only slightly so in S. sila and sordida, but only about half the length of the second lower row in S. puma.

The beaks are well developed and finely serrate in all species. The lower, broadly V-shaped, beak is slender in S. puma, rather robust in S. baudini and sila, and moderately heavy in the other species. The lateral processes of the upper beak are shortest in S. puma and longest in S. baudini and sordida. In the latter the inner margin of the upper beak and lateral process have the form of a shallow S, whereas in the other species the inner margin of the upper beak forms a continuous arch with the lateral processes (Fig. 15).

Coloration.--The tadpoles of Smilisca lack the bright colors or bold markings characteristic of some hylid tadpoles; even so, the subdued colors and arrangement of pigments provide some distinctive markings by which the species can be distinguished from one another. The species comprising the baudini group (S. baudini, cyanosticta, and phaeota) are alike in having the body brown or grayish brown dorsally and transparent with scattered brown pigment ventrally. A cream-colored, crescent-shaped mark is present on the posterior edge of the body; this mark is usually most noticeable in S. baudini and least so in S. cyanosticta. Other differences in coloration in members of the baudini group are relative and subtle. Smilisca phaeota usually is more pallid than baudini, and cyanosticta usually is darker than baudini; both species have larger dark markings on the tail than does S. phaeota. Smilisca baudini has a dark streak on the middle of the anterior one-fourth of the tail (Figs. 11-13).

Smilisca puma is distinctive in having a grayish brown body and dark gray reticulations on the tail. Smilisca sila and sordida are distinctive in having pairs (sometimes interconnected) of dark marks on the dorsal surfaces of the caudal musculature, and in dorsal view the tail appears to be marked with dark and pale creamy tan transverse bars. These dark marks, as well as the small flecks on the tail, are brown in S. sila and red in sordida. Smilisca sila has dark brown flecks on the dorsal surface of the body and small white flecks laterally; these markings are absent in S. sordida (Fig. 14).

Descriptions of the coloration of living tadpoles are given in the accounts of the species.

Growth and Development

Information on the growth and development of Middle American hylids is scanty. Adequate descriptions have been published for Phyllomedusa annae (Duellman, 1963b), Phrynohyas venulosa (Zweifel, 1964), and Triprion petasatus (Duellman and Klaas, 1964). Material is available for adequate descriptions of the developmental stages of four species of Smilisca (Tables 9-12, Figs. 11-13). Because none of the tadpoles was raised from hatching to metamorphosis, the rate of growth and duration of the larval stages are unknown.

Table 9.--Growth and Development of Tadpoles of Smilisca baudini. (Means Are Given in Parentheses After the Observed Ranges.)

==================================================================== Stage | N | Total length | Body length | Tail length -------------------------------------------------------------------- 21 |10 | 5.1-5.4 (5.22) | 2.6-2.7 (2.54) | 2.5-2.7 (2.58) 24 |10 | 6.0-6.5 (6.20) | 2.3-2.6 (2.45) | 3.5-3.9 (3.69) 25 |10 | 7.2-8.3 (7.78) | 3.0-3.3 (3.14) | 4.2-5.0 (4.64) 27 |10 | 18.5-21.5 (20.22) | 8.0-9.0 (8.38) |10.4-13.0 (11.84) 29 |10 | 21.5-24.5 (22.60) | 8.5-10.0 (9.25) |12.5-14.5 (13.35) 37 | 3 | 28.5-31.0 (30.00) |11.0-12.5 (11.67) |17.5-19.0 (18.00) 38 |10 | 35.0-37.5 (35.50) |12.0-13.5 (12.80) |21.5-24.0 (22.70) 40 | 2 | 34.0-37.0 (35.50) |12.5-13.5 (13.00) |21.5-23.5 (22.50) 41 |10 | 34.0-37.0 (35.50) |12.5-13.5 (13.00) |21.5-23.5 (22.50) 42 | 3 | 24.0-30.0 (27.00) |12.5-13.0 (12.67) |11.5-17.0 (14.33) 45 | 6 | 14.0-24.0 (17.58) |12.5-14.0 (13.37) | 1.5-10.0 (4.17) 46 |23 | ---- |12.0-15.5 (13.34) | ---- --------------------------------------------------------------------

Table 10.--Growth and Development of Tadpoles of Smilisca cyanosticta. (Means Are Given in Parentheses After the Observed Ranges.)

====================================================================== Stage | N | Total length | Body length | Tail length ---------------------------------------------------------------------- 21 | 10| 5.8-6.5 (6.28) | 2.8-3.1 (3.00) | 3.0-3.5 (3.28) 25 | 10| 7.9-9.2 (8.44) | 2.7-3.2 (2.96) | 4.8-6.0 (5.48) 30 | 7| 22.5-25.0 (23.50) | 8.5-9.5 (9.00) |14.0-15.5 (14.57) 36 | 10| 27.0-30.0 (28.75) | 9.5-11.5 (10.80) |17.0-18.5 (17.95) 42 | 2| 26.0-27.0 (26.50) | 10.00 |16.0-17.0 (16.50) 46 | 2| -- | 14.00 | -- ----------------------------------------------------------------------

Hatchlings of three species (S. baudini, cyanosticta, and phaeota) are available. These larvae have non-functional eyes and large oral suckers. By the time the larvae have developed to stage 21, external gills are present, the caudal musculature and caudal fin have been differentiated, and the head is distinguishable from the body. In stage 21 oral suckers and a large amount of yolk are still present.