Five km. W of Tangamandapio.
On the night of June 11, 1958, this species was calling from a hyacinth-choked ditch. Although numerous individuals were heard, only one specimen was obtained. The frogs were calling from the tangled mat of hyacinths along with Hyla eximia, Hypopachus oxyrrhinus ovis, and Rana pipiens.
Taylor (1936a:352) characterized this species as follows: "The narrow head, small maximum size (38 mm. for females, 33 mm. for males), the character of the postaxillary and postfemoral glands, the narrower groups of vomerine teeth, clearly distinguish this western Mexican form from the more robust, larger melanonotus to the south. The call is likewise fainter and different in quality." Concerning the glands, Taylor (loc. cit.) remarked: "There is a possibility that the horny excrescence covering the glands may appear only during the breeding season. This character is quite as strongly marked in females as in males." Bogert and Oliver (1945:324) concluded that the population of Leptodactylus in northwestern México could not be distinguished from melanonotus in other parts of the country and thus synonymized Leptodactylus occidentalis with melanonotus. Bogert and Oliver (op. cit.: 324) stated that the extent as well as the presence or absence of ventral glands was highly variable in all samples examined by them.
Upon seeing numerous living individuals of Leptodactylus melanonotus from many parts of its range in México and individuals of the population of Leptodactylus in northwestern México (Nayarit and Sinaloa), I was immediately impressed not so much by the differences in the development of the ventral glands, but by the color of the glands. The differences in color are apparent in freshly preserved specimens. With the exception of Leptodactylus from northwestern México, specimens of melanonotus from throughout México and northern Central America have yellow or yellowish brown glands. Specimens from northwestern México have black or brownish black glands that are conspicuously darker than those found in melanonotus. Examination of 653 preserved specimens of Leptodactylus melanonotus from México and Guatemala has failed to reveal specimens with black ventral glands, like those found in specimens from northwestern México, to which the name Leptodactylus occidentalis has been applied. Furthermore, in melanonotus the glands are less distinct and more extensive than in occidentalis; in the latter species glands are absent from the throat and midventral area, where they often are present in melanonotus (Fig. 7).
In some individuals of both species collected in the dry season and in some collected in the rainy (breeding) season the glands are absent; the development of these glands, therefore, does not seem to be correlated with breeding. Likewise, the glands are present or absent in either sex, and often as not they are present in juveniles. Presence of the glands, therefore, cannot be correlated either with sexual or ontogenetic development. Since the glands are found in individuals from all parts of the range, it is unlikely that there is a correlation between the development of the glands and the environment.
Fig. 7. Diagrammatic view of ventral surfaces of Leptodactylus melanonotus (A) and Leptodactylus occidentalis (B), showing usual position and size of glandular areas. Approx. natural size.
Aside from the differences in the ventral glands, the call is different in the two populations. The call of Leptodactylus occidentalis is a rather harsh "wack, wack, wack" as contrasted with the more nasal "woink, woink, woink" of melanonotus. Sound spectrographs are needed to analyze the differences in calls. None of the specimens of occidentalis examined approaches in size the largest individuals of melanonotus; possibly the size of the frogs is another valid character for separating the species. On the basis of the above data it is evident that the frogs in northwestern México show certain characters that distinguish them from Leptodactylus melanonotus, as it is known throughout the rest of México. It is not known for certain that melanonotus and occidentalis are sympatric. Several series of old, poorly preserved specimens from Nayarit and Sinaloa cannot be placed in either species, for none has visible ventral glands. Leptodactylus melanonotus is known from Acaponeta, Nayarit (AMNH 43913-25), and the following localities in Jalisco: Barro de Navidad (UMMZ 118098), La Concepción (UMMZ 113081), La Resolana (UMMZ 102104), and Tenachitlán (UMMZ 113045-6). Records for Leptodactylus occidentalis are: Álamos, Sonora (AMNH 51356-65); Culiacán (AMNH 49511-9), Chele (UMMZ 110914), and Rosario (UMMZ 113062) in Sinaloa; Ixtlán del Río (UMMZ 102108), San Blas (UMMZ 112814, 112994, 110892, 115543), and Tepic (UMMZ 115544) in Nayarit; Ameca (UMMZ 102106-7) and La Cofradía on the south shore of Lago de Chapala (UMMZ 102105) in Jalisco; and Tangamandapio, Michoacán (UMMZ 119145). From these scattered records it appears that Leptodactylus occidentalis in the southern part of its range stays in the uplands, whereas melanonotus is confined to the lowlands.
Microbatrachylus hobartsmithi (Taylor)
Eleutherodactylus hobartsmithi Taylor, Trans. Kansas Acad. Sci., 39:355, 1937.—Uruapan, Michoacán, México.