PROC. BIOL. SOC. WASH. 
92(3), 1979, pp. 498-504 
A NEW SPECIES OF ELEUTHERODACTYLUS FROM 
NORTHERN ECUADOR (AMPHIBIA: 
LEPTODACTYLIDAE) 
John D. Lynch 
Abstract. — Eleutherodactylus loustes, new species, is described from in- 
termediate elevations on the Pacific versant of the Andes in northern Ec- 
uador. The new species exhibits a combination of character states inter- 
mediate between those of frogs of the fitzingeri and unistrigatus groups and 
differs from all congeners in having toe webbing, areolate skin on the venter, 
and the first finger longer than the second. Its closet relatives are E. cren- 
unguis Lynch and E. latidiscus (Boulenger) from the Pacific versant and E. 
cremnobates Lynch and Duellman and E. rubicundus (Jimenez de la Es- 
pada) from the Amazonian versant. 
Lynch (1976a) defined the species groups of Eleutherodactylus in South 
America primarily on the basis of relative lengths of the inner two fingers 
and the texture of the skin on the venter. The two largest species groups he 
recognized in South America were the fitzingeri group (ca. 40 species) and 
the unistrigatus group (ca. 100 species). Lynch (1976b) and Lynch and 
Duellman (1979) named two species which strained those group definitions. 
Eleutherodactylus crenunguis was placed in the fitzingeri group by Lynch 
(1976b) who noted its resemblance to E. cruentus (Peters) and E. latidiscus 
(Boulenger). Lynch and Duellman (1979) removed E. crenunguis to the 
unistrigatus group, named E. cremnobates, and considered these two 
species closely related to one another as well as to E. rubicundus and E. 
latidiscus; the four species were placed in the rubicundus assembly within 
the unistrigatus group. 
During field work in northern Ecuador in May 1977, an additional species 
of this complex was found. It differs trenchantly from the four species 
known to date in having appreciable toe webbing. 
The following abbreviations are employed: SVL (snout-vent length), lOD 
(interorbital distance), E-N (eye to nostril distance), and KU (University of 
Kansas Museum of Natural History). 
Eleutherodactylus loustes, new species 
(Figs. 1,2) 
Holotype. — KU 179234, an adult female, one of a series collected at Mal- 
donado, Provincia Carchi, Ecuador, 1410 m, on 29 May 1977 by Thomas 
Berger, David Cannatella, and John Lynch. 
VOLUME 92, NUMBER 3 499 
Fig. 1. Eleutherodactylus loustes (KU 179233), adult male, 31.2 mm SVL; from Koda- 
chrome by author. 
Paratypes. —KU 179231-33, 179235-50, collected at the type locality on 
29 and 30 May 1977. 
Diagnosis. — 1) skin of dorsal surfaces smooth except for anastomosing 
ridgelets on lower back and prominent fold between eyes, that of venter 
areolate; no dorsolateral folds; 2) tympanum concealed beneath skin, an- 
nulus small; 3) snout round in dorsal view, angularly rounded in lateral 
profile; 4) upper eyehd broader than lOD, bearing low warts; low cranial 
crests palpable; 5) vomerine odontophores elevated, oval; 6) males with 
vocal slits and subgular vocal sac; no nuptial pad on thumb; 7) first finger 
slightly longer than second; fingers II-IV bearing enlarged pads; all pads 
bearing broad discs; 8) fingers bearing distinct lateral fringes; 9) no ulnar 
tubercles except small antebrachial; 10) no tubercles on heel or tarsus; flap- 
Uke inner tarsal fold on distal ^s-Vi of tarsus; 11) two metatarsal tubercles, 
inner oval, 8 times size of subcorneal outer; 3-6 indistinct supernumerary 
plantar tubercles; 12) toes bearing prominent flap-like lateral fringes, 
webbed— modal formula I 2—2 II 12/3—3" III 2+— 31/2 IV 31/2—2+ V; 
fringe along outer edges of toes I and V; toe pads smaller than those of 
outer fingers; 13) brown above with darker brown markings on occiput and 
sacrum; labial and limb bars, canthal-supratympanic stripes dark brown; 
anterior and posterior surfaces of thighs brown; throat gray; venter cream 
with diffuse brown reticulation; 14) adults large, males 31.2- 37.1 (x = 34.8, 
N = 6), one adult female 46.7 mm SVL. 
Eleutherodactylus loustes is distinguished from its nearest relatives (E. 
cremnobates, E. crenunguis, E. latidiscus and E. rubicundus) by virtue of 
its toe webbing and inner tarsal fold. 
Description. — Head as wide as (or wider than) body; head wider than 
long; head width 38.0-40.9 {x = 39.5, N = 10) percent SVL; snout suba- 
500 
PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
Fig. 2. Eleutherodactylus loustes. A, B, dorsal and lateral views of head, KU 179242; C, 
ventral view of foot, KU 179243. Line equals 5 mm. 
cuminate to round in dorsal view, angularly rounded in lateral profile; nos- 
trils weakly protuberant, directed dorsolaterally; snout short, E-N of males 
67.8-81.6 {x = 74.8, A^ = 6) percent eye length, of females 85.2-91.5 (x = 
88.7, A^ = 4) percent; canthus rostralis evident but rounded, weakly con- 
cave (Fig. 2); loreal region concave, gently sloping to Hps; lips not flared; 
interorbital space narrow, bearing an interocular ridge with a median tu- 
bercle; cranial crests palpable; upper eyehd width 100.0-150.0 (x = 121.5, 
N = 10) percent lOD; low, non-elevated tubercles on upper eyelids; thick 
supratympanic fold from posterior corner of eye to above insertion of upper 
arm; postrictal tubercles large, elevated; tympanic annulus concealed be- 
neath thick skin of side of head (Fig. 2); choanae large, oval, longer than 
wide, not concealed by palatal shelf of maxillary arch when roof of mouth 
is viewed from directly below; vomerine odontophores elevated, oval, me- 
VOLUME 92, NUMBER 3 501 
dian and posterior to choanae, separated by a distance equal to between % 
and a full width of an odontophore, each slightly larger than a choana, 
bearing a transverse row of 4-5 teeth in males, 7-8 teeth in large females; 
tongue large, as long as wide, posterior edge deeply notched, posterior Vs 
not adherent to floor of mouth; males having long vocal slits posterolateral 
to tongue; vocal sac external, subgular, single. 
Skin of dorsal surfaces smooth except for small anastomosing ridges; vent 
extended in a sheath to level of posterior edge of thigh but not going down 
on to back of thighs; skin of venter areolate; throat smooth except for small, 
white warts; forearm bearing small antebrachial tubercle, but no other ulnar 
tubercles; palmar tubercles low; palmar tubercle bifid, twice as large as oval 
thenar tubercle; supernumerary palmar tubercles large, diffuse; subarticular 
tubercles low, round; fingers bearing keel-like lateral fringes and large pads 
(2-3 times width of digit below pad) bearing broader than long discs on 
fingers II-IV; pad of thumb small but bearing broad disc; all pads and discs 
apically rounded (not emarginate); male lacking nuptial pad on thumb; first 
finger longer than second. 
Heel lacking tubercles or bearing one indistinct tubercle; outer edge of 
tarsus lacking tubercles; inner edge of tarsus bearing strong (flap-like) inner 
tarsal fold along distal ^Is to Vi of tarsus; inner metatarsal tubercle flat, oval, 
outer metatarsal tubercle subconical, Vs size of inner; plantar supernumerary 
tubercles indistinct (if present at all); subarticular tubercles not elevated; 
prominent fringe along inner edge of toe I and lesser fringe along outer edge 
of toe V; toe pads slightly smaller than those of outer fingers; toes basally 
webbed (Fig. 2), free portions of toes bearing very prominent lateral fringes; 
webbing formulae (following Savage and Heyer, 1967) for males I (2-2~) — 
(2+-2) II (I24-I1/2)— (3--2-) III (21/4-2)— (3%-3i/3) IV (3l/2-3l^)— (2V5-2) V, 
for females I 2"— (2+-2) II (P/^- 1 1/2)— (21/2-3") III (2+-2-) —(32/^-31/2) IV 
3i/2_(2+_2-) V; shank of males 56.8-63.1 {x = 59.2, N = 6) percent SVL, 
of females 58.8-61.3 (x = 60.4, N = 4) percent. 
Ground color brown; body bearing dark brown occipital W-shaped mark, 
interorbital bar, broad sacral chevron (almost a band); occipital W bearing 
indistinct ridges outlined with cream; interorbital bar bearing cream line 
along anterior border; sacral chevron outlined in cream; dark bars on thighs 
brown separated by pale brown interspaces which are subdivided by dusky 
brown lines; posterior surfaces of thighs dusky brown; dark brown bars on 
shanks as wide as (or slightly narrower than) pale brown interspaces, shank 
bars more or less perpendicular to limb axis; canthal-supratympanic stripe 
and labial bars dark brown; indefinite slanted bars on flanks; anterior sur- 
faces of thighs brown with small cream spots; throat gray with white flecks; 
venter cream with diffuse brown reticulation; throat and venter pigmenta- 
tion separated by diffuse brown V-shaped mark; undersides of limbs gray 
flecked with white and bearing diffuse brown reticulation. 
502 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
In life, E. loustes is colored as follows: "Large female: reddish brown 
with black spots. Some green wash on spaces between leg bars and on lower 
flank. Concealed thigh black with greenish speckles. Iris deep brown. Ven- 
ter cream with brown spots. Throat brown with cream flecks. Toe webs 
pale yellow-green. Male: green with gold or copper wash, especially ante- 
riorly. Iris more coppery [otherwise like female]" (J. D. Lynch fieldnotes 
29 May 1977). 
Measurements of holotype in mm. — SVL 46.7; shank 28.5; head width 
19.1; head length 16.1; upper eyelid width 4.5; lOD 3.3; eye length 6.0; E- 
N5.3. 
Natural history. — Specimens were collected on the nights of 29 and 30 
May 1977 on bare rock faces, moss encrusted rocks on the floor of the 
stream, and on leaves in the spray zone of a waterfall. The small stream 
(a tributary of the Quebrada Naranjo) was heavily shaded by forest. When 
approached with a headlamp the frogs crouched against the wet substrate. 
Collecting one hundred meters on either side of the small waterfall failed to 
yield additional specimens nor were specimens encountered in seemingly 
similar microhabitats along the nearby Quebrada Huagambi (both debauch 
into the Rio San Juan within 200 m). No evidence of reproductive activity 
was noted although males have swollen testes. Two females (JDL 8641-42) 
are slightly smaller (44.9 and 46.0 mm SVL) than the holotype and have 
feebly convoluted oviducts. 
Etymology. — Greek, meaning one fond of bathing. The name is in loose 
allusion to the frogs being found only within the spray zone of a waterfall 
in a deep, cool canyon. 
Sympatric congeners. — In addition to E. loustes, E. achatinus (Boulen- 
ger), E. chalceus (Peters), E. calcarulatus Lynch, E. necerus Lynch, and 
E. w-nigrum (Boettger) were secured in five nights of fieldwork (27-3 1 May 
1977). One other species found at Maldonado is being described separately 
(Lynch and Myers, MS). None of these were found in the same microhabitat 
as E. loustes. 
Discussion. — Lynch and Duellman (1979) suggested that E. crenunguis 
(Pacific) and E. rubicundus (Amazonian) were a species pair in the rubi- 
cundus assembly and that E. cremnobates (Amazonian) and E. latidiscus 
(Pacific) were a second pair. Eleutherodactylus loustes is much more similar 
to E. crenunguis and E. rubicundus than to E. cremnobates or E. latidiscus. 
All five species share the following character states: interorbital space 
narrow, cranial crests present (usually adult females only), fingers and toes 
long and slender and bearing large pads (and broad discs); vomerine odon- 
tophores prominent; canthus rostralis obsolete (not sharp); loreal region 
sloping gently to lips. The tympanic annulus is small in all species but is 
concealed beneath the skin only in E. loustes. That species also differs from 
VOLUME 92, NUMBER 3 
503 
Table 1. Character states in the five species of the rubicundus assembly of the unistrigatus 
group of Eleutherodactylus (x = yes, O = no). 
cremnobates 
crenunguis 
latidiscus 
loustes 
rubicundus 
Male with vocal slits 
o 
X 
o 
X 
o 
First finger > second 
o 
X 
o 
X 
X 
Venter finely areolate 
X 
O 
X 
X 
X 
Digital pads emarginate 
o 
X 
X 
O 
X 
Heel and tarsal tubercles 
X 
X 
O 
O 
X 
Lateral fringes on fingers 
X 
O 
X 
X 
O 
the others in having toe webbing, prominent toe fringes, and a flap-hke inner 
tarsal fold. 
All five species are nocturnal. Eleutherodactylus cremnobates, E. loustes, 
and E. rubicundus are found in very wet areas (often spray zones or drip 
zones) along small rocky streams (0.5-1.5 m wide) in dense cloud forests. 
Eleutherodactylus crenunguis is sometimes encountered in such situations 
but is more frequently found in forest-edge microhabitats. Eleutherodactylus 
latidiscus is a lowland forest species and specimens have accumulated slow- 
ly. The apparent rarity may reflect the frogs' preference for a higher stratum 
in the forest than that normally searched. Richard Zweifel obtained a calhng 
male 4 meters above ground on ''a 6" diameter partly hollow and branchless 
snag, laden with bromehads." 
Those characteristics readily reduced to discrete character states (Table 
1) do not obviously correlate with the ecological notes now available for the 
five species (nor do they readily correlate with my views on the relationships 
among the five species). However, neither do they sort the taxa geograph- 
ically. 
Collections of eleutherodactyline frogs in Ecuador are extensive and al- 
though much data remain to be pubHshed (including approximately 25 un- 
described species), no other eleutherodactyline species are known to me 
that might be closely related to this assembly of five species. A critical point 
is the absence of rubicundus assembly frogs at elevations above 1700 me- 
ters. The reported distribution of E. latidiscus covers eastern Panama, west- 
ern Colombia, and northwestern Ecuador (Cochran and Goin, 1970) but the 
Panamanian material as well as much of the Colombian material is misiden- 
tified. I have examined E. latidiscus as far north as the drainage of the Rio 
San Juan in Colombia and as far south as the Rio Palenque Biological Station 
in southern Provincia Pichincha in Ecuador. Cochran and Coin's (1970) E. 
latidiscus tamsitti, if distinct, establishes the occurrence of the species in 
the headwater regions of the Rio Magdalena. 
The presence of two sets of species found in low cloud forests on opposite 
504 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 
sides of the Ecuadorian Andes where each set has trans-Andean and cis- 
Andean representatives poses a clue to the role of the Andes in the im- 
pressive speciation of Eleutherodactylus in northwestern South America. 
The distributional and phylogenetic patterns suggest that the Andean orog- 
eny isolated the crenunguis-loustes and the latidiscus stocks from those 
of rubicundus and cremnobates respectively. 
Acknowledgments . — Specimens were loaned by William E. Duellman and 
Richard G. Zweifel. Duellman, Alice Grandison, Ron Heyer, and Zweifel 
provided working space and other amenities at their respective institutions. 
Travel to museums was supported by the University of Nebraska Research 
Council. Funds for field work were provided by a grant from the American 
Philosophical Society and a Summer Research Fellowship (University of 
Nebraska Research Council). Thomas Berger and David Cannatella aided 
me in the field. 
Literature Cited 
Cochran, D. M., and C. J. Goin. 1970. Frogs of Colombia.— U.S. Nat. Mus. Bull. 288, 655 
pp. 
Lynch, J. D. 1976a. The species groups of the South American frogs of the genus Eleuther- 
odactylus (Leptodactylidae). — Occ. Pap. Mus. Nat. Hist. Univ. Kansas 61:1-24. 
. 1976b. New species of frogs (Leptodactylidae: Eleutherodactylus) from the Pacific 
versant of Ecuador. — Occ. Pap. Mus. Nat. Hist. Univ. Kansas 55:1-33. 
Lynch, J. D., and W. E. Duellman. 1979. The Eleutherodactylus of the Amazonian slopes of 
the Ecuadorian Andes (Anura: Leptodactylidae). — Misc. Publ. Univ. Kansas Mus. Nat. 
Hist, in press. 
Savage, J. M., and W. R. Heyer. 1967. Variation and distribution in the tree-frog genus 
Phyllomedusa in Costa Rica, Central America. — Beit. Neotrop. Fauna 5:111-131. 
School of Life Sciences, The University of Nebraska, Lincoln, Nebraska 
68588.