Part 13

=Phrynohyas modesta= Taylor and Smith

Oaxaca: Tuxtepec. Veracruz: 20 km. S of Jesus Carranza; 20 km. ENE of Jesus Carranza (2); Minatitlan.

I have not collected this species in the isthmus. The locality records indicate that the range is discontinuous (Duellman, 1956:27). The species occurs on the humid Pacific slopes from south-central Chiapas eastward to El Salvador and on the humid Gulf lowlands from southern Veracruz eastward into Tabasco, but is unknown from the dry Pacific slopes and plains in the isthmus.

The acquisition of several specimens of this species in southern Veracruz, Tabasco, and Oaxaca, together with a knowledge of the variation displayed by Phrynohyas spilomma, suggests that modesta may be a color variety of spilomma.

=Phrynohyas spilomma= Cope

Oaxaca: Tapanatepec (3). Veracruz: Amatitlan (12); Chacaltianguis (2); Ciudad Aleman (6); Cosamaloapan; Novillero (3).

Like the preceding species, this frog is unknown from the arid Pacific lowlands of the isthmus; its presence at Tapanatepec, a locality situated in more mesic conditions than prevail on the Plains of Tehuantepec, indicates that it may have a distribution on the Pacific slopes much like that of P. modesta. Furthermore, this frog was not detected in the rainforests of the Gulf lowlands; in that region it was found only in scrub forest and savanna.

On July 26, 1956, numerous choruses of these frogs were heard between Ciudad Aleman and Tlacotalpan, Veracruz. The call is a loud, nasal "grawl" repeated continuously. The males call from the water. Several clasping pairs were found in shallow grassy ponds amidst the scrub forest. The ground color varies from reddish brown to tan with dark brown dorsal markings. The iris is golden, and the vocal sacs are dark olive brown. After a light shower during the dry season, six individuals were found on the low branches of trees at night near Ciudad Aleman.

=Phyllomedusa callidryas taylori= Funkhouser

Oaxaca: Donaji (9); Sarabia (8); Tolosita (6); Ubero (27). Veracruz: Alvarado (7); Aquilera; Berta; Coatzacoalcos (9); 10 km. SE of Hueyapan (5); Naranja (17).

In life this frog presents a striking array of colors. The dorsum varies from pale green to dark olive green; there may be scattered whitish or cream-colored spots on the back. On the flanks are bright yellow to deep cream-colored vertical bars separated by pale blue or purple interspaces. The thighs and undersurfaces of the hind limbs are golden orange; the belly is yellow, and the throat is cream-colored. The iris is crimson; the transparent part of the lower eyelid has golden reticulations. When the frog is resting, the forefeet are folded beneath the throat, and the limbs are folded tightly against the body. In this position and with the eyes closed and head flattened, this gaudy frog assumes the appearance of a small elliptical green leaf.

Throughout the month of July, 1956, Phyllomedusa was breeding in ponds in or adjacent to the rainforest in northern Oaxaca and in southern Veracruz. Only at Alvarado was it found breeding in a grassy pond. Males and females alike were found on bushes and trees in and around the ponds. The call is a single "wank." Amplexing males continue to call, but the call is softer and less nasal in quality. The eggs are encased in pale green gelatin and attached to leaves on branches overhanging the water. Three egg clutches contained 38, 41, and 46 eggs.

=Phyllomedusa dacnicolor= Cope

Oaxaca: Escurano; Tehuantepec.

Although it is abundant on the Pacific lowlands to the northwest in Guerrero, Michoacan, and Colima, this species is known only from two specimens from Tehuantepec. There is no apparent physical barrier to their distribution in the isthmus; in the Balsas Basin the species lives in a hotter, more arid environment than that at Tehuantepec.

=Gastrophryne usta= Cope

Oaxaca: Santa Efigenia; Tehuantepec (10); 24 km. W of Tehuantepec; Tolosita (2). Veracruz: Ayentes (6); La Oaxaquena; Novillero (2); San Lorenzo.

Calling males were found in open scrub forest near Tehuantepec and in savannas near Novillero. The specimens from Tolosita were found under cover in a clearing in the forest (Fugler and Webb, 1957:106).

Specimens from the Pacific lowlands are typical of Gastrophryne usta gadowi Boulenger in possessing a thin line on the posterior surface of the thighs and a thin line from the snout to the vent. Of nine specimens from the Gulf lowlands (Ayentes, Novillero, and San Lorenzo), seven have a middorsal line; this is narrow in four and wide in three. Five have the stripes on the thighs. Two specimens from the middle of the isthmus (Tolosita) have no stripes on the thighs; one has a thin middorsal line, and the other has a broad line. The adult males have a black throat; females have a mottled one. The brown reticulations on the bellies of specimens from the Gulf lowlands is bolder than on specimens from the Pacific lowlands. The presence of certain characters supposedly diagnostic of the subspecies gadowi (line on dorsum and thighs) in the population of usta in southern Veracruz suggests that a redefinition of the ranges of these subspecies will be in order when sufficient material is available to delimit them accurately. For the present I prefer to consider all specimens from the isthmus solely as Gastrophryne usta without referring them to subspecies.

=Rana palmipes= Spix

Oaxaca: Matias Romero (11); 11 km. S of Santiago Chivela; Santo Domingo; Sarabia. Veracruz: Coatzacoalcos; Cuatotolapam; 25 km. SE of Jesus Carranza (4); Tlacotalpan (2); Tula.

Adults were found along streams and in marshes in savannas and rainforest. These frogs are wary and difficult to capture, even at night. Rana palmipes is another species that has a discontinuous distribution in the isthmus. The species does not occur on the Pacific lowlands of the isthmus, but does occur on the more humid Pacific slopes of Chiapas and Guatemala.

Tadpoles were found in a small sluggish tributary to the Rio Sarabia.

=Rana pipiens= Schreber

Oaxaca: Agua Caliente; Cerro Quiengola; Escurano (14); Rio Sarabia (2); Tapanatepec (5); Tehuantepec (24). Veracruz: Acayucan; Cuatotolapam (15); Jesus Carranza (2); 20 km. S of Jesus Carranza (11); 25 km. SE of Jesus Carranza; 20 km. ENE of Jesus Carranza (10); San Lorenzo (10).

As in most other places in Mexico and northern Central America, this species occurs wherever there is permanent water. Males were heard calling from woodland ponds and from savanna ponds.

SUMMARY

Investigations of the amphibians and their environments in the Isthmus of Tehuantepec have been presented with the aim of gaining an understanding of the present biological and of the historical events responsible for the present patterns of distribution of amphibians in this region.