A Taxonomic Revision of the Leptodactylid Frog Genus Syrrhophus Cope Part 6

Dixon and Webb (1966) reported that _S. nivocolimae_ has a large tympanum (50.0-59.0 per cent diameter of eye). However, my examination of the type series and several other specimens from Jalisco reveals that the largest tympanum/eye ratio is 39.3 per cent. Therefore, the tympanum/eye ratio in _S. nivocolimae_ is in agreement with those for _S. modestus_, _S. pallidus_, and _S. teretistes_ (Table 6).

_Etymology._--_niv_, Latin, and Colima (Nevado de), meaning high on the volcano, in reference to the higher distribution of this species (around 2000 meters) than other members of the group.

_Distribution._--Known from southwestern Jalisco, Mexico, at moderate to high elevations (600-2400 meters).

_Specimens examined._--(48) MeXICO, _Jalisco_: 17.6 km. SW Autlan, 606 m., KU 102626, 102631; 6.4 km. W Atenquique, 2060 m., KU 102628-30, 102632; 8 km. W Atenquique, 1970 m., LACM 3210-12; 9.6 km. W Atenquique, 2360 m., LACM 3200 (holotype), 3201-09; 14.5 km. W Atenquique, 2000 m., LACM 25424-36, 25439-41, 25446; 15 km. W Atenquique, LACM 37044-46, 37244-47; 16 km. W Atenquique, 2105 m., LACM 25443-45; 17 km. W Atenquique, 2180 m., LACM 25442.

=Syrrhophus pallidus= Duellman, New combination

_Syrrhophus modestus_: Davis and Dixon, 1957:146.

_Syrrhophus modestus pallidus_ Duellman, 1958:2-3, 5-7, 14, pl. 3 [Holotype.--UMMZ 115452, from San Blas, Nayarit, Mexico, sea level; collected on August 13, 1956, by William E. and Ann S.

Duellman]. Zweifel, 1960:86-88, 91, 93-94, 118, 120-22. Gorham, 1966:166.

_Syrrhophis modestus pallidus_: Campbell and Simmons, 1962:194.

_Diagnosis._--Small frogs, males 17.9-19.3 mm. snout-vent length; vocal slits in males; finger tips widely expanded; first finger shorter than second; inner metatarsal tubercle about three times size of outer; skin of dorsum s.h.a.greened, that of venter smooth; tympanum concealed, its diameter 27.0-35.6 per cent of eye in males; ground color cream vermiculated with brown, upper arm and thigh lacking, or with few, indistinct, bands; interorbital bar absent.

_Remarks._--Considerable debate has been waged relative to the value of subspecies and to the reasons for recognizing distinct disjunct populations as species versus subspecies. Lacking evidence of genetic exchange, I prefer to retain disjunct populations that are distinctive as species.

All known specimens of _pallidus_ can be separated from those of _modestus_ by color pattern. The two nominal species exhibit overlap in proportions but the same can be said about nearly every species of _Syrrhophus_; therefore, overlap in proportions can be disregarded in a.s.sessing specific versus subspecific rank. Until contrary evidence is forthcoming, I consider the disjunct populations heretofore held to be subspecies of _modestus_ to be specifically distinct. The specimens of the disjunct population of _pallidus_ on the Tres Marias do not differ from the mainland population in Nayarit. This evidence, though perhaps secondary, supports my contention that two species should be recognized.

_Etymology._--Latin, in reference to the pale ground color in comparison with that of _S. modestus_.

_Distribution._--Low elevations in coastal Nayarit and on Islas Tres Marias (Fig. 20).

_Specimens examined._--(12) MeXICO, _Nayarit_: 18.8 mi. NW Ahuacatlan, UIMNH 7808; San Blas, UMMZ 115452 (holotype), 115453-57; 17 km. NE San Blas, 150 m., MSU 5085; 12.8 km. E San Blas, UIMNH 71979; 31 km. E San Blas, UIMNH 71978; 13.5 km. N Tepic, UIMNH 71980-81.

=Syrrhophus teretistes= Duellman

_Syrrhophus teretistes_ Duellman, 1958:2-3, 10-14, pl. 2, fig. 2 [Holotype.--UMMZ 115451, from 4.8 km. NW Tepic, Nayarit, Mexico, 840 m.; collected on August 12, 1956, by William E. Duellman].

Gorham, 1966:167.

_Diagnosis._--Medium-sized frogs, males 19.2-23.2 mm. snout-vent length, single known female 24.8 mm. snout-vent; vocal slits in males; finger tips widely expanded; first finger shorter than second; inner metatarsal tubercle about three times size of outer; skin of dorsum s.h.a.greened, that of venter smooth; tympanum partially concealed, its diameter 28.6-43.8 per cent of eye in males; ground color brown vermiculated with dark brown to nearly black; upper arm and thigh banded; interorbital light bar absent.

_Remarks._--_S. teretistes_ appears to be most closely related to _S. pallidus_; I consider it to be an upland derivative of _pallidus_.

Morphologically, the differences between the two are few, but lacking evidence of genetic exchange they are retained as species.

_Etymology._--Greek, in reference to the whistle-like nature of the call.

_Distribution._--Moderate elevations (840-1200 meters) in the Sierra Occidental of Nayarit, Sinaloa, and Durango, Mexico (Fig. 20).

_Specimens examined._--(13) MeXICO, _Nayarit_: 4.8 km. NW Tepic, 840 m., UMMZ 115451 (holotype). _Sinaloa_: Santa Lucia, 1090 m., KU 75263-72; 1 km. NE Santa Lucia, 1156 m., KU 78257; 2.2 km. NE Santa Lucia, 1156 m., KU 78258.

DISCUSSION

There are relatively few clear-cut morphological differences among the fourteen species now a.s.signed to _Syrrhophus_. The majority of the species are allopatric and differ primarily in color patterns. Sympatric occurrence serves as an indicator of specific distinctness and is one of the more practical tests of species validity when cross-breeding experiments are not possible. Two cases of sympatric occurrence are known for the species of _Syrrhophus_ in western Mexico: _modestus_ and _nivocolimae_ are sympatric in southern Jalisco and _pipilans nebulosus_ and _rubrimaculatus_ are sympatric in southeastern Chiapas. In eastern Mexico, _longipes_ and _verrucipes_ are sympatric in southern Hidalgo, and _longipes_ is sympatric with _cystignathoides_, _dennisi_, and _guttilatus_ in southern Tamaulipas. _Syrrhophus cystignathoides_ and _leprus_ are apparently sympatric in central Veracruz.

Subspecific a.s.signments have been made only when there is evidence of intergradation. The sympatric occurrence of morphologically similar species in this genus has led me to adopt a conservative approach to the degree of difference philosophy. I have therefore recognized all morphologically distinct allopatric populations as species.

[Ill.u.s.tration: FIG. 21: Generic distributions of _Syrrhophus_ (stipple) and _Tomodactylus_ (hatching). Black areas are zones of intergeneric sympatry.]

_Syrrhophus_ is closely allied to another Mexican leptodactylid genus, _Tomodactylus_, which was revised by Dixon (1957), who along with numerous other authors noted the close relationship between the two genera. There is an almost complete lack of sympatry between the two genera; in very few places in Mexico do they coexist (Fig. 21).

_Tomodactylus_ has its greatest diversity in the Cordillera Volcanica and Sierra Madre del Sur, whereas _Syrrhophus_ reaches its greatest diversity in the Sierra Madre Oriental and eastern foothills. The species of both genera are about the same size and presumably have similar requirements insofar as food, breeding sites, and habitat selection.

Four cases of intergeneric sympatry are known for the two genera: 1) the Chilpancingo region of Guerrero, 2) the lowlands of Colima and the mountains just inland in Jalisco, 3) the lowlands of central Nayarit, and 4) the Sierra Madre Occidental on the Durango-Sinaloan border. The apparent sympatry in the Chilpancingo region involves four species: _S. pipilans_, _T. albolabris_, _T. dilatus_, and _T. nitidus_. Of the four, _T. dilatus_ appears to be completely allopatric in that it occurs at higher alt.i.tudes (above 2000 meters), whereas the other three occur below 1800 meters in the region (Davis and Dixon, 1965). In the Colima-Jalisco region, _Tomodactylus_ tends to occur higher (Dixon and Webb, 1966) than some of the _Syrrhophus_, but one subspecies of _Tomodactylus nitidus_ is a lowland frog, occurring sympatrically with the lowland _Syrrhophus modestus_. A similar situation is observed in Nayarit; the lowland _Tomodactylus_ occurs sympatrically with the small _Syrrhophus pallidus_. In both cases the _Syrrhophus_ is smaller than the _Tomodactylus_.

[Ill.u.s.tration: FIG. 22: Alt.i.tudinal distributions of _Syrrhophus_ and _Tomodactylus_. Widths of the columns are proportional to the numbers of species at a given alt.i.tude; narrowest width equals one species.]

Frogs of the genus _Syrrhophus_ tend to occur at lower elevations than do their close relatives of the genus _Tomodactylus_ (Fig. 22). This generalization is complicated by the occurrence in the Sierra Madre Oriental in relatively high alt.i.tude _Syrrhophus_ (up to 2000 m.) and the occurrence in Michoacan of low alt.i.tude _Tomodactylus_ (to sea level). There are no _Tomodactylus_ in the Sierra Madre Oriental, whereas the genus _Syrrhophus_ is represented in the lowlands of western Mexico (_modestus_ group). _Syrrhophus_ and _Tomodactylus_ exhibit essentially parapatric distributions. The two genera as now composed can be characterized as low to moderate elevation frogs (_Syrrhophus_) and moderate to intermediate elevation frogs (_Tomodactylus_).

LITERATURE CITED

BAIRD, S. F.

1859. Reptiles of the Boundary. United States and Mexican Boundary Survey, pp. 1-35, pls. 1-41.

BARBOUR, T.

1923. The reappearance of Batrachyla longipes. Proc. New England Zool. Club, 8:81-83.

BARBOUR, T., and A. LOVERIDGE

1946. Typical reptiles and amphibians; supplement. Bull. Mus. Comp.

Zool., 96:59-214.

BOULENGER, G. A.

1882. Catalogue of the Batrachia Salientia ... British Museum., 2nd ed.

1888. Note on the cla.s.sification of the Ranidae. Proc. Zool. Soc.

London, 1888, pt. 2:204-06.

CAMPBELL, H. W., and R. S. SIMMONS