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, Michoacán, México, 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 Cañas, Guanacaste Province, Costa Rica. When the pair was grasped, the female emitted a distress call.
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.
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).