Description Leptodactylus pentadactylus, the Smoky Jungle Frog, is a large frog. Adult males can reach 177 mm while the larger females can measure up to 185 mm (Savage 2002). This frog can be distinguished from other frogs by the presence of paired dorsolateral folds, paired lumbar glands, and a spotted or barred upper lip, as well as its large size (Savage 2002). This species has a smooth dorsum, definite inguinal glands, and large eyes and tympana (Savage 2002). The snout is rounded, almost semicircular when viewed from above (Savage 2002). Adult males have paired elongated vocal slits and a single internal subgular vocal sac (Savage 2002). In addition, adult males have extremely muscular forelimbs and a pair of black spines on the chest, plus a black spine on each thumb (Guyer and Donnelly 2005). Dorsolateral folds extend from each eye to the groin (Hero and Galatti 1990). The adult coloration has been described as either uniform gray to reddish brown, or with darker spots or bars on the ground color (Savage 2002), It has also been described as a dark purple and light brown reticulum (Guyer and Donnelly 2005). The underside is dark gray with white to yellow mottling or tiny white speckles (Savage 2002). The posterior thigh has small white spots on a black background. A dark interorbital bar is present (Guyer and Donnelly 2005). Young frogs are more brightly colored than adults and have toe ridges (Savage 2002).
Tadpoles of this species are giant and elongate, growing up to 83 mm at stage 40 (Savage 2002; Hero and Galatti 1990). Dorsally, the tadpole is brown, with a lighter ventral surface (Savage 2002). The mouth is almost terminal, while the nostrils and eyes are on the dorsal side (Savage 2002). The spiracle is located laterally and sinistrally and the vent is medial (Savage 2002). This species has a long tail with low fins and a pointed tail tip (Savage 2002). The oral disk is complete and moderate, having two serrated beaks and 2/3 rows of denticles, with a broad gap in the row of denticles immediately above the mouth (Savage 2002). Labial papillae are lacking above the mouth, but are usually found in two rows lateral to the mouth and a single row ventral to the mouth (Savage 2002). The lateral line system is well-developed, particularly in comparison with larvae of other Leptodactylus species (Heyer et al. 1975).
The Smoky Jungle Frog can be found from Honduras southward into South America. L. pentadactylus is widespread in lowland rainforest on both Atlantic and Pacific slopes of Costa Rica from sea level to 1,200 m (Leenders 2001). It prefers forest habitat near swamps and slowly flowing streams (Guyer and Donnelly 2005). It may also be found inhabiting areas distant from bodies of water (Galatti 1992).
Life History, Abundance, Activity, and Special Behaviors
These frogs can be long-lived and have a potential life-span of at least 15 years (Leenders 2001). Adults are nocturnal and stay in hiding during the day, sheltering in subterranean burrows, beneath logs, in the spaces between tree roots, or under houses (Savage 2002). Juveniles, however, are active during the day and can be found on top of the leaf litter (Savage 2002). This species prefers dimly lit forest (Jaeger and Hailman 1981). At the first sign of dusk, males of this species give off a loud "wrooop" (Leenders 2001). The call lacks pulses (Hero and Galatti 1990). Males are territorial and call sporadically from burrows located underneath a log or rock, often in densely vegetated areas (Leenders 2001).
Mating is believed to take place throughout the rainy season months of May to November (Savage 2002). However, Hero and Galatti (1990) observed that males in the central Amazon region of Brazil began calling immediately after the first substantial rains, in late September, and that calling ceased after two to four weeks. Both calling and breeding take place at the water's edge; it is not known whether the same burrows used for shelter are also used as nest sites (Savage 2002). Amplexus is axillary in this species (Savage 2002). As the male hugs the female under the armpits with his robust forearms, he creates a large foamy mass around the eggs by rapidly moving his back legs through the jelly surrounding the fertilized eggs (Heyer and Rand 1977). This foam nest consists of a frothy mix of sperm, skin secretions, water, and air (Heyer and Rand 1977). Females lay about 1,000 light gray eggs, and the foam nests are constructed in dry cavities or depressions (Savage 2002). These hollows may be natural or possibly excavated by the males (Muedeking and Heyer 1976). Foam nests may be constructed near puddles, temporary pools or in seasonally flooded spots, such that rain washes the larvae out of the nests and into nearby small rain pools (Breder 1946). Alternatively, foam nests have been observed in open depressions at some distance from water, so that tadpoles develop within the nest until metamorphosis (Muedeking and Heyer 1976; Hero and Galatti 1990). In the latter case, Muedeking and Heyer (1976) noted both larvae and eggs in the nests, and inferred that eggs were being consumed by larvae. Leptodactylus pentadactylus larvae are unusually resistant to desiccation for anuran tadpoles, and can survive almost seven days out of water (Valerio 1971). Foam nests also provide protection to larvae from desiccation (Heyer 1969).
Galatti (1992) observed that the strong seasonality in Leptodactylus pentadactylus reproduction in Brazil coincided with arthropod prey availability. He observed two peaks in arthropod abundance, one in late September (when the adults arrived at breeding sites), and the second in January and February, when tadpoles completed metamorphosis into juvenile frogs (Galatti 1992). These peaks did not completely correspond to rainfall, as the first peak in arthropod prey abundance occurred during the late dry season and the second occurred during the wet season (Galatti 1992).
Leptodactylus pentadactylus is able to secrete huge amounts of mucus as an antipredator defense (Savage 2002). In addition to making the frog slippery and difficult to hold, the skin secretions are toxic (Savage 2002). Savage (2002) points out that this toxicity is evident both from direct contact (resulting in human skin rashes and stinging) and indirect contact, from being in the same room when the frog is handled (which results in sneezing and swelling of human eyes and mucus membranes). The residue from these skin secretions is lethal to other frogs which come in contact with it (Savage 2002). Leptodactylus pentadactylus also exhibits defensive behavior, which consists of facing the predator, inflating and elevating the body with all four limbs (Villa 1969; Savage 2002). This has the effect of raising the posterior, glandular surfaces above the level of the head since the hind limbs are longer (Villa 1969; Savage 2002). Initial elevation is followed by repeated raising and lowering of the body (Villa 1969; Savage 2002).
These frogs are opportunistic feeders. Adults consume anything that they can swallow, including bird chicks, snakes, other frogs (particularly dendrobatids, despite their toxicity), and scorpions (Leenders 2001). Tadpoles initially feed on the foam produced by the male, but later will either eat algae (Vinton 1951) or become carnivorous, preying on eggs and tadpoles of their own species or other species (Muedeking and Heyer 1976; Heyer et al. 1975).
Predators on Leptodactylus pentadactylus eggs include the ephydrid fly Gastrops willistoni, which lays its own eggs on L. pentadactylus clutches in Costa Rica and Brazil (Villa et al. 1982). Predators on the adult frogs include coatimundis, snakes, and caimans. When discovered, these frogs often remains still and easily approached. If caught, however, they will emit an extremely loud, high-pitched scream to startle potential predators (Leenders 2001).
Research has shown that these frogs have an accurate visual image of their surroundings, though it is not known exactly what cues they use for orientation (Leenders 2001). Frogs taken from their burrows and displaced over short distances have managed to return to their burrow in a straight line (Leenders 2001).
Adult Leptodactylus pentadactylus are negatively phototactic (avoid light), unlike most anurans (Kicliter and Goytia 1995).
Trends and Threats Leptodactylus pentadactylus is not endangered. This species is fairly common (Savage 2002).
Relation to Humans These frogs have been reported to be occasionally consumed by Amazonian people (Leenders, 2001). The karyotype is 2N=22 (Bogart 1974).