Chapter V: Part 5

The upper frequency range varies within each species and even within the calls of one individual. _Smilisca phaeota_ has the lowest upper frequencies; no calls ranged above 4400 cycles per second (cps.), and half of the calls never exceeded 3000 cps. _Smilisca cyanosticta_ produces calls in which the upper frequency is below 7000 cps. and usually below 6000 cps. Likewise, _S. puma_ produces calls that are below 7000 cps., whereas _S. sila_ has frequencies of up to 8400 cps. In both _S. baudini_ and _S. sordida_, the highest frequencies attained are about 9100 cps. Variation in the highest frequencies in a series of consecutive calls by one individual frog was noted in all species. Such variation is especially prevalent in _S. puma_; for example one individual (KU 87771; Tape No. 376) recorded at a temperature of 24 deg. C. at 7.5 kilometers west of Puerto Viejo, Heredia Province, Costa Rica, on July 31, 1964, produced three consecutive primary notes having upper frequencies of about 6000, 4000, and 4000 cps., respectively. Apparently in a given species the production of the higher frequencies in some notes and not in others is correlated with the amount of distention of the vocal sac and is not dependent upon the structure or tension of the vocal cords.

Although the dominant frequency in _S. sordida_ is lower than that in _S. baudini_ and _S. cyanosticta_, the call of the former is audibly higher-pitched. This is due primarily to the emphasis on certain harmonics at a high frequency (sometimes as high as 9000 cps.) in _S. sordida_, whereas in _S. baudini_ and other species, if harmonics are present at those frequencies, they are not emphasized.

The fundamental frequencies are as low as 90 cps. in _S. sila_ and _S. sordida_ and as high as 200 cps. in _S. puma_ (Table 8). The fundamental frequency seemingly is relatively unimportant in determining the general pitch of the call, a characteristic most dependent on the dominant frequency and emphasized harmonics in the higher-frequency spectrum. In none of the species is the fundamental the dominant frequency. In the low-pitched call of _S. phaeota_ the dominant frequency is the third harmonic (the second harmonic above the fundamental frequency, which is the first harmonic). In all other species a much higher harmonic is dominant; for examples, in _S. cyanosticta_ harmonics from 10 to 15 are dominant; in _S. baudini_, 15-19; and _S. sila_, 20-30.

A glance at the audiospectrographs and their accompanying sections (Pls. 10 and 11) reveals the presence of two emphasized bands of frequency in all species except _S. phaeota_, in which only the lower band is present. These two bands of emphasized harmonics are part of a continuous, or nearly continuous, spread of energy throughout the frequency spectrum, except in _S. sordida_ in which the bands are usually distinct. As shown in the sections, certain harmonics in each of the bands are emphasized with nearly equal intensity. Therefore, with the exception of _S. phaeota_, the calls of _Smilisca_ are characterized by two major frequencies, one of which is the dominant frequency and the other is a subdominant frequency (Table 8). The upper major frequency is dominant in all calls in _S. baudini_ and _S. cyanosticta_, but either major frequency may be dominant in other species. The upper major frequency is dominant in 65 per cent of calls by _S. puma_, 87 per cent in _S. sila_, and 68 per cent in _S. sordida_. Individuals of these three species sometimes produce a series of calls in which the dominant frequency changes from one of the major frequencies to the other. Four consecutive notes emitted by an individual of _S. sordida_ recorded 13 kilometers east-northeast of Golfito, Puntarenas Province, Costa Rica, had dominant frequencies of 910, 1950, and 750 cps., respectively. In each case, an alternation of major frequencies took place in respect to dominance. An individual of _S. puma_ from 7.5 kilometers west of Puerto Viejo, Costa Rica, produced a primary note followed by one secondary note; each note had major frequencies at 600 and 1800 cps.; the dominant frequency of the primary note was at 1800 cps., whereas in the secondary note the dominant frequency was at 600 cps. The difference in emphasis on the major frequencies is so slight that shift in dominance is not audible.

_Effect of temperature on calls._--The present data are insufficient to test statistically the correlation between temperature and variation within certain components of the calls in _Smilisca_, but even a crude graph shows some general correlations. The widest range of temperatures is associated with the recordings of _S. baudini_. Three individuals recorded at a temperature of 30 deg. C. at Tehuantepec, Oaxaca, had pulse rates of 180 pulses per second and fundamental frequencies of 160-180 cps., as compared with an individual recorded at a temperature of 17 deg. C., which had a pulse rate of 140 and a fundamental frequency of 135 cps. All individuals of _S. baudini_ recorded at higher temperatures had faster pulse rates and higher fundamental frequencies. Pulse rates differ in the other species in the genus but less strikingly (probably owing to narrower ranges of temperatures at which recordings were made). In five recordings of _S. sordida_ made at 20 deg. C. the pulse rate is 80-90, as compared with four recordings made at 25 deg. C. having pulse rates of 120-135. Thirteen recordings of _S. sila_ made at 17 deg. C. have pulse rates of 97-112 (average 105); one individual recorded at 26 deg. C. has 120 pulses per second. Seemingly no correlation exists between temperature and other characteristics of the calls, such as duration and rate of note-repetition.

_The breeding call as an isolating mechanism._--Blair (1958), Bogert (1960), Duellman (1963a), Fouquette (1960), Johnson (1959), and others have provided evidence that the breeding calls of male hylids (and other anurans) serve as isolating mechanisms in sympatric species. In summarizing this discussion of the breeding calls of _Smilisca_ we want to point out what seem to be important differences in the calls that may prevent interspecific hybridization in sympatric species of _Smilisca_.

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.

The developmental data on the four species show no significant variations; consequently, we will describe the development of only one species, _Smilisca phaeota_ (Table 11, Figs. 13 and 16).

_Stage 21._--Bulging cream-colored yolk mass, transparent cornea, and moderately long, unbranched filamentous gills, and oral suckers present; mouth having irregular papillae on lower lip; teeth and beaks absent; caudal myomeres distinct; pigmentation uniform over body and caudal musculature; caudal fin transparent with scattered small flecks.

_Stage 25._--Operculum complete; gills absent; sinistral spiracle apparently functional; cloacal tail-piece, nasal capsules, and external nares present; gut partly formed; mouth bordered by single row of papillae, except medially; small papillae present in lateral fold of lips; two upper and three lower tooth-rows present, but not fully developed; beaks apparently fully developed; depth of dorsal and ventral fins less than depth of caudal musculature: tip of tail upturned; pigment on body most dense on dorsum and sides; faint, nearly pigmentless crescent-shaped mark on posterior edge of body; concentrations of pigment forming small spots on tail.

_Stage 28._--Mouthparts complete; limb bud about half as long as thick; other structural features and coloration closely resemble those in stage 25.

_Stage 30._--Limb bud approximately twice as long as thick; body as deep as wide; dorsal fin deepest just posterior to body; ventral fin deeper than caudal musculature; tail sharply upturned distally; anal tube dextral; brown pigment sparse on flanks.

Table 11.--Growth and Development of Tadpoles of Smilisca phaeota.
(Means Are Given in Parentheses After the Observed Ranges.)

====================================================================
Stage | N | Total length | Body length | Tail length
--------------------------------------------------------------------
15 | 10| -- | 1.9-2.1 (1.97) | --
16 | 8| -- | 2.0-2.2 (2.07) | --
18 | 4| -- | 2.2-2.6 (2.31) | --
21 | 3| 7.9-8.6 (8.21) | 4.1-4.5 (4.31) | 3.8-4.1 (3.92)
25 | 10| 8.7-10.6 (9.69) | 4.5-4.8 (4.64) | 4.3-6.0 (5.05)
26 | 11| 12.3-16.1 (14.01) | 4.2-6.3 (5.60) | 6.7-9.8 (8.41)
27 | 10| 13.0-15.7 (14.28) | 4.9-6.2 (5.40) | 7.7-10.5 (8.88)
28 | 13| 13.9-20.9 (15.62) | 5.2-8.3 (5.75) | 8.5-12.6 (9.85)
29 | 8| 17.8-22.3 (19.79) | 6.3-8.4 (7.19) | 11.5-14.0 (12.60)
30 | 9| 20.3-24.8 (22.85) | 8.1-10.5 (9.32) | 10.5-15.5 (13.53)
31 | 5| 24.1-28.5 (26.61) | 9.4-11.2 (10.59) | 14.7-17.3 (16.02)
34 | 5| 24.8-29.4 (27.31) | 9.2-11.6 (10.73) | 15.6-18.5 (16.80)
36 | 3| 30.0-30.1 (30.07) |10.1-12.2 (11.15) | 18.9-20.0 (19.44)
37 | 4| 28.9-34.1 (31.75) |11.5-12.4 (11.88) | 17.4-22.5 (19.88)
38 | 1| 28.98 |12.88 | 16.10
39 | 2| 35.6-36.9 (36.25) |14.00 | 21.6-22.9 (22.25)
40 | 2| 32.3-39.8 (36.05) |14.00 | 18.3-21.8 (20.05)
43 | 2| 21.5-23.0 (22.25) |14.2-14.8 (14.45) | 6.8-8.8 (7.80)
44 | 4| -- |14.5-15.6 (15.08) | --
46 | 11| -- |12.7-16.7 (14.26) | --
--------------------------------------------------------------------

Table 12.--Growth and Development of Tadpoles of Smilisca sordida.
(Means Are Given in Parentheses After the Observed Ranges.)

=======+===+==================+==================+=================
Stage | N | Total length | Body length | Tail length
-------+---+------------------+------------------+-----------------
25 | 6 | 25.5-28.0 (26.1) | 9.0-9.5 (9.3) | 16.2-18.5 (16.7)
33 | 2 | 28.5-30.0 (29.3) | 10.2-10.5 (10.4) | 18.0-19.8 (18.9)
36 | 8 | 29.5-34.5 (32.3) | 10.2-11.7 (10.8) | 19.3-23.0 (21.5)
37 | 7 | 31.6-37.5 (34.6) | 11.0-12.5 (11.5) | 21.6-25.0 (23.2)
41 | 3 | 33.0-37.2 (35.2) | 11.6-12.2 (11.9) | 21.4-25.2 (23.2)
43 | 1 | ---- | 12.4 | ----
46 | 9 | ---- | 13.1-15.7 (14.9) | ----
-------+---+------------------+------------------+-----------------

_Stages 34_, _36_, _37_, and _38_.--Stage 34, foot paddle-shaped with four toe buds; stage 36, five toe buds; stages 37 and 38, lengthening of toes. In all four stages, spiracle persistent, and pigmentation resembling that of early stages.

_Stage 39._--Metatarsal tubercle present; greatest total length (36.9 mm.) attained.

_Stage 40._--Subarticular tubercles prominent; skin over forelimbs transparent; cloacal tail-piece and spiracle absent; outer tooth-rows degenerating; caudal fins shallower than in preceding stages; distal part of tail nearly straight; size of dark markings on tail decreased; pigment present on hind limb.

_Stage 43._--Forelimbs erupted; larval mouthparts absent; corner of mouth between nostril and eye; transverse bands present on hind limbs; tail greatly reduced (about 8 mm. in length).

_Stage 44._--Sacral hump barely noticeable; tail reduced to a stub; corner of mouth at level of pupil of eye; dorsal surfaces pale olive-green; venter white.

Changes proceed in a definite pattern during the growth and development of tadpoles. Larval teeth are absent in hatchlings; the inner tooth-rows develop first, and the third lower row last. At metamorphosis the third lower row is the first to be lost. The tail increases gradually in length relative to the body. In stage 25 the tail is 52.1 per cent of the total length, and in stage 36, 64.6 per cent. In later stages the tail becomes relatively shorter through resorption. Duellman and Klaas (1964:320) noted a great size-variation in _Triprion_ tadpoles in stage 25. No such variation is apparent in any stage of any of the species of _Smilisca_ studied.

The growth and development of the other species of _Smilisca_ do not differ significantly from that of _S. phaeota_. The tadpoles of _S. sila_ and _sordida_ from streams have relatively longer tails at hatching. For example, in tadpoles of _S. sordida_ the average length of tail is 64.0 per cent of the body-length in stage 25, and in stage 37, 67.0 per cent.

_Behavior_

The tadpoles of _S. baudini_, _cyanosticta_, _phaeota_, and _puma_ are pelagic inhabitants of shallow ponds. Early stages of _S. baudini_ in which external gills are present have been observed to hang vertically with the gills spread out at the surface of the water, a behavior noted by Zweifel (1964:206) in tadpoles of _Phrynohyas venulosa_, which also develop in warm, standing water having a relatively low oxygen-tension. When disturbed the pelagic tadpoles usually dive and seek shelter amidst vegetation or in mud on the bottom. This behavior was observed in _S. baudini_, _cyanosticta_, and _phaeota_ by day and at night. No tadpoles of _S. puma_ were observed by day; those seen at night were near the surface of small water-filled depressions in a grassy marsh; they responded to light by taking refuge in the dense grass. Perhaps tadpoles of this species are negatively phototactic and remain hidden by day.

The stream-inhabiting tadpoles of _S. sila_ and _sordida_ live in clear pools in rocky streams, where they were observed to cling by their mouths to rocks in the stream and to seek shelter amidst pebbles or beneath rocks and leaves on the bottom. These tadpoles are not found in shallow riffles.

We have not found tadpoles of two species of _Smilisca_ in the same body of water and therefore cannot offer observations on ecological relationships in sympatric situations.

PHYLOGENETIC RELATIONSHIPS

Identifiable hylid remains are known from the Miocene to the Recent, but these fossils are mostly fragmentary and provide little useful information regarding the phylogenetic relationships of living genera. Frogs of the genus _Smilisca_ are generalized and show no striking adaptations, either in their structure or in their modes of life history.

Interspecific Relationships

In attempting to understand the relationships of the species of _Smilisca_ we have emphasized osteological characters. The phylogeny suggested by these characters is supported by other lines of evidence, including external morphology, tadpoles, and breeding calls.

Our concept of the prototype of the genus _Smilisca_ is a moderate-sized hylid having: (1) a well-developed frontoparietal fontanelle, (2) frontoparietal lacking lateral processes, (3) no bony squamosal-maxillary arch, (4) a fully ossified ethmoid, (5) paired subgular vocal sac, (6) moderately webbed fingers and toes, (7) relatively few supernumerary tubercles on the digits, (8) eggs deposited in clumps in ponds, (9) anteroventral mouth in tadpoles bordered by one row of labial papillae, but median part of upper lip bare, (10) tail relatively short and deep in tadpoles, and (11) a breeding call consisting of a series of like notes.

Two phyletic lines evolved from this prototype. The first of these was the stock that gave rise to the _baudini_ group. The evolutionary changes that took place in this line included increase in size, development of a lateral curvature of the maxillary, and an increased amount of cranial ossification, especially in the dermal roofing bones. This phyletic line retained the larval characters and breeding call of the prototype. The second phyletic line gave rise to the _sordida_ group and diverged from the prototype in the development of an angular maxillary and a breeding call consisting of a primary note followed by secondary notes. The frogs in this phyletic line retained the moderate size of the prototype and did not develop additional dermal bone. Our concept of the phylogenetic relationships is shown graphically in Figure 17.

Within the _baudini_ group one stock retained separate nasals and did not develop a bony squamosal-maxillary arch, but broad lateral processes developed on the frontoparietals. The tadpoles remained unchanged from the primitive type. This stock evolved into _S. phaeota_. In the other stock the nasals became fully ossified and a bony squamosal-maxillary arch developed. One branch of this second stock retained tadpoles having only one row of labial papillae and did not develop lateral processes on the frontoparietals; this branch evolved into _S. cyanosticta_. The other branch diverged and gave rise to _S. baudini_ by developing relatively shorter hind legs, large lateral processes on the frontoparietals, and tadpoles having two rows of labial papillae.

Within the _sordida_ group the cranial features remained unchanged in one line, which gave rise to _S. sila_, whereas in a second line the nasals were reduced, and their long axes shifted with the result that they are not parallel to the maxillaries; the amount of ossification of the ethmoid was reduced, and the tadpoles developed two rows of labial papillae. In this second line one branch retained the pond-breeding habits and gave rise to _S. puma_, whereas a second branch became adapted to stream-breeding and gave rise to _S. sordida_.

_baudini_
\ _cyanosticta_
\ /
+ _phaeota_ _sordida_
\ / /
+ puma_ /
\ \/ _sila_
\ /_____/
\ /
\ /
\ /
|
|
Prototype

Certain aspects of this proposed phylogeny warrant further comment. Features such as the deposition of additional bone that roofs the skull or that forms lateral projections from the frontoparietals, like those in _S. baudini_ and _phaeota_, are minor alterations of dermal elements and not basic modifications of the architecture of the skull. Consequently, we hypothesize the independent development of these dermal changes in _S. baudini_ and _phaeota_. Similar kinds of dermal modifications have evolved independently in many diverse groups of frogs.

Likewise, we propose the parallel development of stream-adapted tadpoles in _S. sordida_ and _sila_; in both cases the tadpoles adapted to changing environmental conditions (see following section on evolutionary history). Tadpoles of _S. sordida_ already had two rows of labial papillae before entering the streams; subsequently the tadpoles developed complete rows of papillae, ventral mouths and long tails having low fins. Possibly the tadpoles of _S. sila_ had two rows of labial papillae prior to their adapting to stream conditions; in the process of adapting they developed ventral mouths and long tails having low fins. Similar modifications in tadpoles have occurred in many diverse groups of Middle American hylids, such as _Plectrohyla_, _Ptychohyla_, the _Hyla uranochroa_ group, and the _Hyla taeniopus_ group.

Our lack of concern about coloration is due to the fact that, with the exception of the blue spots on the flanks and posterior surfaces of the thighs in some species, the coloration of _Smilisca_, consisting of a pattern of irregular dark marks on a paler dorsum and dark transverse bars on the limbs, is not much different from that of many other Neotropical hylids. Blue is a structural color, rare among Amphibia, which is achieved by the absence of lipophores above the guanophores. Thus, the incident light rays at the blue end of the spectrum are reflected by the guanophores without interference by an overlying yellow lipophore screen. According to Noble (1931), lipophores are capable of amoeboid movement that permits shifts in their positions, between or beneath the guanophores. We do not know whether this behavior of lipophores is widespread and is effected in response to environmental changes, or whether it is a genetically controlled attribute that is restricted in appearance. If the latter is the case we must assume that the prototype of _Smilisca_ possessed such an attribute which was lost in _S. baudini_, _phaeota_, and _puma_. The development of blue spots is not constant in _S. sordida_ and _S. sila_; in _S. cyanosticta_ the spots range in color from blue to pale green.

The coloration of the tadpoles is not distinctive, except for the presence of dorsal blotches on the tails of _S. sila_ and _sordida_. However, the similarity in pattern cannot be interpreted as indicating close relationships because nearly identical patterns are present in _Hyla legleri_ and some species of _Prostherapis_. This disruptive coloration seems to be directly associated with the pebble-bottom, stream-inhabiting tadpoles.

In the _baudini_ group, _S. phaeota_ and _cyanosticta_ are allopatric, whereas _S. baudini_ occurs sympatrically with both of those species. The call of _S. baudini_ differs notably from the calls of _S. phaeota_ and _cyanosticta_, which are more nearly alike. Although in the phylogenetic scheme proposed here _S. sila_ is considered to be more distantly related to _S. puma_ than is _S. sordida_, the calls of _S. sila_ and _puma_ more closely resemble one another than either resembles that of _S. sordida_. _Smilisca sila_ and _puma_ are allopatric, whereas _S. sordida_ is broadly sympatric with both of those species. We assume that in their respective phyletic lines the differentiation of both _S. baudini_ and _sordida_ was the result of genetic changes in geographically isolated populations. Subsequently, each species dispersed into areas inhabited by other members of their respective groups. Selection for differences in the breeding calls helped to reinforce other differences in the populations and thereby aided in maintaining specificity.

Evolutionary History

With respect to temporal and spatial aspects of evolution in _Smilisca_, we have tried to correlate the phylogenetic evidence on _Smilisca_ with the geologic data on Middle America presented by Lloyd (1963), Vinson and Brineman (1963), Guzman and Cserna (1963), Maldonado-Koerdell (1964), and Whitmore and Stewart (1965). Likewise, we have borne in mind the evidence for, and ideas about, the evolution of the Middle American herpetofauna given by Dunn (1931b), Schmidt (1943), Stuart (1950, 1964) Duellman (1958, MS), and Savage (MS).

According to Stuart's (1950) historical arrangement of the herpetofauna, _Smilisca_ is a member of the Autochthonous Middle American Faunal Element, and according to Savage's (MS) arrangement the genus belongs to the Middle American Element, a fauna which was derived from a generalized tropical American unit that was isolated in tropical North America by the inundation of the Isthmian Link in early Tertiary, that developed _in situ_ in tropical North America, and that was restricted to Middle America by climatic change in the late Cenozoic.

Savage (MS) relied on the paleogeographic maps of Lloyd (1963) to hypothesize the extent and centers of differentiation of the Middle American Faunal Element. According to Lloyd's concept, Middle America in the Miocene consisted of a broad peninsula extending southeastward to about central Nicaragua, separated from the Panamanian Spur of continental South America by shallow seas. A large island, the Talamanca Range, and remnants of the Guanarivas Ridge formed an archipelago in the shallow sea. The recent discovery of remains of mammals having definite North American affinities in the Miocene of the Canal Zone (Whitmore and Stewart, 1965) provides substantial evidence that at least a peninsula was continuous southeastward from Nuclear Central America to the area of the present Canal Zone in early mid-Miocene time. South America was isolated from Central America by the Bolivar Trough until late mid-Pliocene.

Thus, in the mid-Tertiary the broad peninsula of Nuclear Central America, which consisted of low and moderately uplifted regions having a tropical mesic climate, provided the site for the evolution of _Smilisca_. It is not possible to determine when the genus evolved, but to explain the differentiation of the species it is unnecessary to have the ancestral _Smilisca_ present prior to the Miocene.

We view the Miocene _Smilisca_ as the prototype described in the preceding section, and suppose that it lived in the mesic tropical environment of the eastern part of the Central American Peninsula (in what is now Costa Rica and western Panama). Two stocks differentiated, probably in middle Miocene times; one of these, the ancestral stock of the _baudini_ group, was widespread on the Caribbean lowlands from the Nicaraguan Depression to the Bolivar Trough, and the other, the ancestral stock of the _sordida_ group, was restricted to the Pacific lowlands of the same region. In late Miocene time the ancestral stock of the _baudini_ group dispersed northwestward around the deep embayment in the Nicaraguan depression into upper Central America (in what is now Honduras and Guatemala) and thence into southern Mexico. Apparently differentiation took place on each side of the Nicaraguan Depression; the frogs to the south of the depression evolved into _S. phaeota_, whereas those to the north of the depression represented the stock from which _S. baudini_ and _cyanosticta_ arose. Prior to the uplift of the mountains in the late Miocene and the Pliocene the _baudini-cyanosticta_ stock probably was widespread in northwestern Central America. The elevation of the mountains resulted in notable climatic changes, principally the development of sub-humid environments on the Pacific lowlands. The frogs living on the Pacific lowlands became adapted to sub-humid conditions and developed into _S. baudini_. The stock on the Caribbean lowlands remained in mesic environments and evolved into _S. cyanosticta_.

Possibly in the middle Miocene before the Talamanca Range in Costa Rica and western Panama was greatly uplifted, the ancestral stock of the _sordida_ group invaded the Caribbean lowlands of what is now Costa Rica. The subsequent elevation of the Talamanca Range in the Pliocene effectively isolated the ancestral stock of _S. sila_ on the Pacific lowlands from the _puma-sordida_ stock on the Caribbean lowlands. The former was subjected to the sub-humid conditions which developed on the Pacific lowlands when the Talamanca Range was uplifted. It adapted to the sub-humid environment by living along streams and evolving stream-adapted tadpoles. On the Caribbean side of the Talamanca Range the _puma-sordida_ stock inhabited mesic environments. The stock that evolved into _S. puma_ remained in the lowlands as a pond-breeding frog, whereas those frogs living on the slopes of the newly elevated mountains became adapted for their montane existence by developing stream-adapted tadpoles and thus differentiated into _S. sordida_.

Probably the six species of _Smilisca_ were in existence by the end of the Pliocene; at that time a continuous land connection existed from Central America to South America. The climatic fluctuations in the Pleistocene, and the post-Wisconsin development of present climatic and vegetational patterns in Middle America, brought about the present patterns of distribution of the species. From its place of origin on the Caribbean lowlands of lower Central America, _S. phaeota_ dispersed northward into Nicaragua and southward along the Pacific slopes of northwestern South America. Perhaps in the late Pleistocene or in post-Wisconsin time when mesic conditions were more widespread than now, _S. phaeota_ moved onto the Pacific lowlands of Costa Rica. Its route could have been through the Arenal Depression. Subsequent aridity restricted its range on the Pacific lowlands to the Golfo Dulce region. Climatic fluctuation in northern Central America restricted the distribution of _S. cyanosticta_ to mesic habitats on the slopes of the Mexican and Guatemalan highlands and to certain humid areas on the lowlands. _Smilisca baudini_ was well adapted to sub-humid conditions, and the species dispersed northward to the Rio Grande Embayment and to the edge of the Sonoran Desert and southward into Costa Rica. In southern Mexico and Central America the species invaded mesic habitats. Consequently, in some areas it is sympatric with _S. cyanosticta_ and _phaeota_.

_Smilisca puma_ dispersed northward onto the Caribbean lowlands of southern Nicaragua. Its southward movements probably were limited by the ridges of the Talamanca Range that extend to the Caribbean coast in the area of Punta Cahuita in Costa Rica. _Smilisca sila_ dispersed along the Pacific lowlands and slopes of the mountains from eastern Costa Rica and western Panama through eastern Panama to northern Colombia. Climatic fluctuation in the Pleistocene evidently provided sufficient altitudinal shifts in environments in the Talamanca Range to permit _S. sordida_ to move onto the Pacific slopes. From its upland distribution the species followed streams down to both the Caribbean and Pacific lowlands, where it is sympatric with _S. puma_ on the Caribbean lowlands and _S. sila_ on the Pacific lowlands.

The evolution of the species-groups of _Smilisca_ was effected through isolation by physical barriers in the Cenozoic; the differentiation of the species was initiated by further isolation of populations by changes in physiography and climate. Present patterns of distribution resulted from Pleistocene and post-Wisconsin climatic changes. Today, sympatric species have different breeding habits and breeding calls which reinforce the differences in morphology.

SUMMARY AND CONCLUSIONS

The genus _Smilisca_ is composed of six species of tree frogs; each species is defined on the basis of adult morphology, larval characters, and breeding behavior. Keys are provided to aid in the identification of adults and of tadpoles.

Analysis of the characters and examination of type specimens indicates that several currently-recognized taxa are synonymous, as follows:

1. _Hyla beltrani_ Taylor, 1942 = _Smilisca baudini_.
2. _Hyla gabbi_ Cope, 1876 = _Smilisca sordida_.
3. _Hyla manisorum_ Taylor, 1954 = _Smilisca baudini_.
4. _Hyla nigripes_ Cope, 1876 = _Smilisca sordida_.
5. _Hyla wellmanorum_ Taylor, 1952 = _Smilisca puma_.

_Smilisca phaeota cyanosticta_ Smith, 1953 is elevated to specific rank, and one new species, _Smilisca sila_, is named and described.

The skeletal system of developmental stages and the adult of _Smilisca baudini_ is described, and the skull is compared with that of other members of the genus.

The tadpoles are described, compared, and illustrated; the larval development of _Smilisca phaeota_ is described.

Breeding behavior and breeding calls are described and compared. Some species of _Smilisca_ have breeding choruses. Two species, _S. sila_ and _sordida_, breed in streams, whereas the others breed in ponds.

The genus is considered to be part of the Middle American Faunal Element; the species are thought to have differentiated in response to ecological diversity and historical opportunities provided by Cenozoic changes in physiography and climate.

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_Transmitted March 14, 1966._

[]
31-3430

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Index. Pp. 651-681.

*Vol. 4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466,
41 plates, 31 figures in text. December 27, 1951.

Vol. 5. Nos. 1-37 and index. Pp. 1-676, 1951-1953.

*Vol. 6. (Complete) Mammals of Utah, _taxonomy and distribution_. By
Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
August 10, 1952.

Vol. 7. Nos. 1-15 and index. Pp. 1-651, 1952-1955.

Vol. 8. Nos. 1-10 and index. Pp. 1-675, 1954-1956.

Vol. 9. Nos. 1-23 and index. Pp. 1-690, 1955-1960.

Vol. 10. Nos. 1-10 and index. Pp. 1-626, 1956-1960.

Vol. 11. Nos. 1-10 and index. Pp. 1-703, 1958-1960.

Vol. 12. *1. Functional morphology of three bats: Eumops, Myotis,
Macrotus. By Terry A. Vaughan. Pp. 1-153, pls. 1-4,
24 figures in text. July 8, 1959.

*2. The ancestry of modern Amphibia: a review of the
evidence. By Theodore H. Eaton, Jr. Pp. 155-180,
10 figures in text. July 10, 1959.

3. The baculum in microtine rodents. By Sidney Anderson.
Pp. 181-216, 49 figures in text. February 19, 1960.

*4. A new order of fishlike Amphibia from the Pennsylvanian
of Kansas. By Theodore H. Eaton, Jr., and Peggy Lou
Stewart. Pp. 217-240, 12 figures in text. May 2, 1960.

5. Natural history of the Bell Vireo, Vireo bellii Audubon.
By Jon C. Barlow. Pp. 241-296, 6 figures in text.
March 7, 1962.

6. Two new pelycosaurs from the lower Permian of Oklahoma.
By Richard C. Fox. Pp. 297-307, 6 figures in text.
May 21, 1962.

7. Vertebrates from the barrier island of Tamaulipas,
Mexico. By Robert K. Selander, Richard F. Johnston,
B. J. Wilks, and Gerald G. Raun. Pp. 309-345, pls. 5-8.
June 18, 1962.

8. Teeth of edestid sharks. By Theodore H. Eaton, Jr.
Pp. 347-362, 10 figures in text. October 1, 1962.

9. Variation in the muscles and nerves of the leg in two
genera of grouse (Tympanuchus and Pedioecetes).
By E. Bruce Holmes. Pp. 363-474, 20 figures in text.
October 25, 1963. $1.00.

10. A new genus of Pennsylvanian fish (Crossopterygii,
Coelacanthiformes) from Kansas. By Joan Echols.
Pp. 475-501, 7 figures in text. October 25, 1963.

11. Observations on the Mississippi kite in southwestern
Kansas. By Henry S. Fitch. Pp. 503-519. October 25, 1963.

12. Jaw musculature of the Mourning and White-winged doves.
By Robert L. Merz. Pp. 521-551, 22 figures in text.
October 25, 1963.

13. Thoracic and coracoid arteries in two families of birds,
Columbidae and Hirundinidae. By Marion Anne Jenkinson.
Pp. 553-573, 7 figures in text. March 2, 1964.

14. The breeding birds of Kansas. By Richard F. Johnston.
Pp. 575-655, 10 figures in text. May 18, 1964. 75 cents.