Elachistocleis erythrogaster Kwet & Di-Bernardo 1998

Elachistocleis erythrogaster is a small sized frog with an egg-shaped body and a snout-vent length ranging from 29 – 32 mm in males and 34 – 37 mm in females. It has a lengthy, curved snout that protrudes from its small, triangular head. It has prodigious choanae that is separated by a considerable distance and a big, ovular tongue. The nostrils, which are pointed anterolaterally, do not protrude and are separated by a relatively narrow internarial distance (~1.6 mm). Elachistocleis erythrogaster has a curved canthus rostralis and a level loreal region that has a sharp incline just above the lip. It has relatively small eyes that protrude a minimal amount and an interorbital region that is almost 2.5 times the diameter of each eye. Its tympanum are obscured. Elachistocleis erythrogaster has a discrete skinfold that goes laterally from the posterior portion of the head behind the eyes to the groin and another that goes across the chest between the two forelimb insertions. It has a large gland located posterior to the mouth corners and the skin located both dorsally and ventrally to the gland is smooth. Its cloacal vent points posterodorsally. It has short, plump forelimbs. Elachistocleis erythrogaster has small, ovular inner metacarpal tubercles that protrude slightly, large, longitudinally divided outer metacarpal tubercles, and small, circular subarticular tubercles. Elachistocleis erythrogaster has no supernumerary tubercles. The fingers do not terminate with grooves and have relative lengths of 1 < 2 < 4 < 3, with the third finger being about 1.5 times the length of the fourth. The hindlegs are short and plump. It doesn’t have any tubercles on the heels or knees, outer metatarsal tubercles, or supernumerary tubercles. However, the inner metatarsal tubercles are large and ovular and the subarticular tubercles are large and circular. The hindlegs end in unwebbed toes without lateral fringes. The toe terminals are not expanded and they have relative lengths of 1 < 2 < 5 < 3 < 4 (Kwet and Di-Bernardo 1998).Elachistocleis erythrogaster is differentiated from other species of its genus by its deep black throat in both females and males, its sky-blue and deep black streaks on its lateral surface, and its flame-orange ventral surface with irregularly shaped sky-blue and deep black splotches on the posterior portion of the venter. It is easily differentiated from Elachistocleis ovalis, which occurs in the same region, by their differing adult morphology, coloration, advertisement call, and reproductive behaviors. Elachistocleis erythrogaster is larger than E. ovalis as an adult and also has a larger clutch size, larger eggs, and larger tadpoles. Elachistocleis erythrogaster has a louder and longer call than E. ovalis composed of fewer pulses and with a dominant frequency 1000 Hz lower than E. ovalis. Elachistocleis erythrogaster does not have the femoral stripe on the posterior surface of the thigh that is present in E. ovalis. Finally, whereas E. ovalis has tadpoles with chocolate-brown dorsal surfaces and slightly pigmented fins, E. erythrogaster has tadpoles with chocolate-brown dorsal and lateral surfaces and transparent fins with a curved tip. Elachistocleis ovalis tadpole tail ends in a sharp point. (Kwet and Di-Bernardo 1998).In life, male Elachistocleis erythrogaster have deep black dorsal surfaces with streaks and splotches of sky-blue and flame-orange. Females of this species have flame-orange dorsal surfaces with streaks and splotches of sky-blue and deep black. The coloration of the dorsal surfaces of the limbs resembles that of the dorsum. The ventral surfaces of the limbs are flame-orange but on the hindlimbs that region is smaller due to the overlap of the deep black and sky-blue from the dorsal surfaces. There is no femoral stripe on the thighs and the lateral surfaces are sky-blue marbled with deep black. Elachistocleis erythrogaster has a flame-orange venter with irregularly shaped deep black splotches and sky-blue spots on the posterior half of the venter. The throat is deep black and has sky-blue marbling laterally. At the corner of the mouth is an irregularly shaped flame-orange splotch. In preservative, all dorsal surfaces are beige to chocolate-brown and are darker in males than in females. The marbled colors are not as clear as in life and the blue color does not show. The flame-orange ventral surfaces grow to a dull yellow but still display the irregular black spolotches. The throat remains black. Preserved, juvenile Elachistocleis erythrogaster have chocolate-brown ventral and dorsal surfaces except for several transparent spots on the chest, forelimb, and mouth (Kwet and Di-Bernardo 1998).The dark splotches on the venter are usually found toward the posterior end, although they may extend anteriorly in some specimens. The flame-orange background of the venter has varying degrees of brightness (Kwet and Di-Bernardo 1998).The species authority is: Kwet, A., and Di-Bernardo M. 1998. Elachistocleis erythrogaster, a New Microhylid Species from Rio Grande do Sul, Brazil. Studies on Neotropical Fauna and Environment 33(1): 7-18.Elachistocleis erythrogaster is part of the Ovalis-Bicolor species complex (Kwet and Di-Bernardo 1998).The species was named for its red vent, where “erythros” means red and “gaster” means venter in Greek (Kwet and Di-Bernardo 1998).Elachistocleis erythrogaster is only the second microhylid know from the Rio Grande do Sol (Kwet and Di-Bernardo 1998).

Elachistocleis erythrogaster are found in the grasslands of the Araucaria plateau (Planalto das Araucarias) in Rio Grand do Sul, Sao Francisco de Paula and Sao Francisco de Cambara, Serra Geral, Brazil. They appear to be restricted to the southeastern border of the plateau (Kwet and Di-Bernardo 1998).

Elachistocleis erythrogaster individuals were found during heavy rains on warm (18oC) nights. At the time males were heard calling from the early evening, gradually decreasing until after midnight. Their loud, long call was first mistaken for E. ovalis. The call consists of high-pitched, loud whistles lasting 3.9 – 4.2 seconds at a dominate frequency ranging from 3100 – 4500 Hz and a pulse rate of 110 – 125 pulses per second. Call characterization included an increase in frequency at the beginning of the call and repeated 1 – 3 times intermittently per minute. Males were found calling in vertical positions between blades of tall grass with their posterior ends in 10 – 20 cm deep water (Kwet and Di-Bernardo 1998).During mating, males bind themselves to females using axillary amplexus and with a strong glue-like secretion. Two mating pairs brought into captivity laid 991 and 476 eggs, respectively. The black eggs were approximately 2.5 mm in diameter and formed a thin egg film on the surface of the after (Kwet and Di-Bernardo 1998).In January 2001, anti-predator behavior of E. erythrogaster, triggered by light touching, was observed in five of six individuals. It consisted of the frogs inflating their lungs and straightening their hindlimbs, which the frogs held for approximately one minute. Elachistocleis erythrogaster also produced a white, sticky skin secretion, of which the toxicity is unknown but assumed to be noxious to predators. The frogs, however, did not expose their ventrums during the anti-predator response, making the function of their bright coloration currently unknown (Kwet and Sole 2002). It is assumed that E. erythrogaster feed on termites and ants because of the well formed dermal fold behind the eyes that is known to protect E. ovalis from ants. It is also assumed that E. erythrogaster is fossorial and remains hidden most of the year, making it difficult to find and study (Kwet and Di-Bernardo 1998).

While the population trend of E. erythrogaster is stable, because of its limited range it is vulnerable to decline, thus justifying a near threatened IUCN Red List status. The only known threat is habitat loss to cattle ranching (Silvano et al. 2004).

Diagnosis Elachistocleis erythrogaster is easily distinguished from all other known species of this genus by the deep black throat in males and females, its black and bright blue marbled lateral surface, and its flashy redorange venter with some irregular black and bright blue speckled blotches towards the posterior. Furthermore it differs from the sympatric E. bicolor in its advertisement call, and lack of femoral stripe.

Restricted to the southeastern border of the Araucaria plateau (Planalto das Araucárias), Serra Geral, Estado do Rio Grande do Sul, southern Brazil.

Description of the Holotype Body ovoid; snout-vent length 32.3 mm. Head small, triangular; head width 7.2 mm; snout long, eye-nostril distance 2.5 mm, broadly rounded in dorsal view, strongly protruding in lateral view. No vomerine teeth; choanae large and widely separated; tongue large, oval. Nostrils not protuberant, directed anterolaterally, close to tip of snout; internarial distance narrow, internarinal distance 1.6 mm. Canthus rostralis rounded; loreal region flat, sloping abruptly to above lip. Eyes small, diameter 1.9 mm , sligthly projecting; interorbital region flat; interorbital distance 4.5 mm. Tympanum concealed. A distinct skinfold running from back of the head laterally slightly behind the eyes to groin. Another skinfold crossing chest between axillae. Massive gland behind the corner of mouth; skin above and below smooth. Vent opening positioned posterodorsally. Forelegs short, moderately robust. Inner metacarpal tubercle small, moderately raised, oval; outer metacarpal tubercle large, low, divided longitudinally; small subarticular tubercles, low, rounded; no supernumerary tubercles. Relative lengths of fingers 3>4>2>1, fourth about two-thirds length of third. Tips of fingers not flattened or expanded, terminal grooves absent. Hindlegs stout, short; thigh length 11.1 mm; tibia length 10.2 mm; foot length 12.1 mm. No tubercles on knee and heel; inner metatarsal tubercle prominent, oval, moderately raised; no outer metatarsal tubercle; subarticular tubercles prominent, rounded; no supernumerary tubercles. Relative lengths of toes 4>3>5>2>1. Toes unwebbed, without lateral fringes. Tips of toes not expanded. Coloration in life: dorsum of male dark, marbled with black, blue and some orange; dorsum of female orange, marbled with black and blue. Dorsal surface of limbs with coloration like dorsum; ventral red-orange, on hindlimbs restricted to a smaller area being the larger part black, mottled with bright blue. No femoral stripe on the posterior surface of thigh. Lateral surface bright blue, mottled with black. Venter flashy red-orange, with some irregular black blotches speckled with bright blue, restricted to the posterior parts, or expanded up to half of the whole venter. Throat uniformly black, at the edges mottled with bright blue. At angular region of the mouth a small irregular formed red-orange fleck. In preservative (70% ethanol): dorsum of body and limbs tan to brown, in males even darker; mottling less evident than in life. Blue coloration absent. Red flashy color of venter faded to yellow, with uniform black blotches. Throat black. Variation There is little variation in external morphology and dorsal coloration, the latter being different between sexes as described above. Distinct size differences between female and male exist, the former being larger than the latter. As described above, the ventral coloration varies in form and extension of the dark blotches, and in degree of the red-orange ground color which in life normally is flashy, but in living specimen MCP 2451 was much fainter and more yellowish.The only known juvenile, a preserved and faded specimen (MCN 4201), shows a nearly uniform brown ventral and dorsal coloration, except for some clearer blotches at chest, forelimb and mouth. Larval morphology Larva in stage 29 (Gosner, 1960). Typical free-swimming pond tadpole; suspension feeder. Total length about 17 mm. Body lenght 0.4 of total length. Body 1.4 times longer than wide; 1.8 times longer than high; 1.3 times wider than high. Body ovoid in dorsal view, depressed in lateral view; widest at midlength. Eyes small, widely separated, dorsolaterally positioned; interorbital distance nearly equal to body width. Nostrils small, narrow separated, dorsal. Snout in dorsal view broad, rounded; in lateral view rounded with appendage. Mouth small, terminal; lacking keratinized mouthparts and papillae; two pendant flaps separated by a medial notch enclosing the mouth dorsally. Vent opening midventral, positioned at posterior margin of body. Single spiracle near vent tube, posterior, midventral; spiracle opening directed to the left side of the vent opening. Tail musculature highest at tail-body junction, narrowing gradually posteriorly. In lateral view, dorsal and ventral fins highest at midlength, extending towards tip of tail. Dorsal fin extending towards body, slightly higher than ventral fin for entire length. Ventral fin about equal to musculature height at midlength. Tip of tail rounded. In preservative dorsal and lateral coloration of body dark brown; below eyes scarcely pigmented; ventrally clear, nearly transparent, scarcely speckled with pigments. Tail musculature dark brown; dorsal and ventral fins transparent.

NT. Near Threatened. Listed how vulnerable (VU) in the Lista Vermelha do Estado do Rio Grande do Sul.

Elachistocleis erythrogaster is a species of frog in the family Microhylidae. It is endemic to Brazil. Its natural habitats are moist savanna, subtropical or tropical seasonally wet or flooded lowland grassland, intermittent freshwater marshes, and pastureland. It is threatened by habitat loss.