Ingerophrynus parvus (Boulenger 1887)

Bufo parvus is a small toad, with females of this species typically being larger than the males. Females have a snout-vent length of 40-50 mm while the males reach a snout-vent length of 30-35 mm. This toad has a short snout. A supraorbital ridge and a pair of parietal ridges are present. The skin is wrinkled and bears tubercles or warts. No tubercles are present behind the parotoid gland. The toes are half-webbed. Adult B. parvus can be brown, black, or reddish in color while the juveniles are brown in color. Adults also generally have a pair of symmetrical black spots on the mid-back. Males usually have a reddish throat (Iskandar, 1998). The tadpoles are small, with the tail usually no longer than double the head plus body length, and a denticle formula of I+1-1/III. Papillae are confined to the corner of the mouth, and the mouth is not adapted for stream-dwelling (Iskandar, 1998). Inthara et al. (2005; p. 78) provide a drawing of the larval mouthparts of Bufo parvus compared to eight other tadpole species of Thailand.Bufo parvus is toxic, with skin extract doses of 100 mg/mouse causing locomotor difficulties, prostration convulsions, and death in 2 hours (Daly et al., 2004). This frog is very similar to Bornean populations of B. biporcatus in morphology and behavior (Inger et al., 1974). Bufo parvus can be distinguished by its smaller size and by the lack of tubercles behind the parotoid gland (present in B. biporcatus), as well as by having a pair of symmetrical black blotches on the back (absent in B. biporcatus) (Iskandar, 1998). The species name uses the Latin word parvus, meaning small (Iskandar, 1998).

This toad occurs in forests and rubber plantations from peninsular Thailand and Burma throughout the Malay peninsula (Inger et al., 1974). It inhabits both primary and secondary forest, and can also be found in gardens (Iskandar, 1998).

This species disperses on the forest floor more than 30 m from streams, so that the nonbreeding ranges are distinct from their breeding sites (Inger et al., 1974). Females of this species lay clutches of several hundred eggs in stagnant or slowly moving waters (Iskandar, 1998) consisting of rocky pools alongside small streams less than 10 m wide (Inger et al., 1974). Bufo parvus forms semi-isolated breeding aggregations, and calling, amplexing, and oviposition occurs at the same site (Inger et al., 1974).

This species is not threatened.

The lesser toad, or dwarf stream toad, Ingerophrynus parvus, is occurs widely at lowland altitudes up to 550 m asl across western and Peninsular Thailand, Peninsular Malaysia, southern Myanmar, Indonesia and isolated populations in southeastern Thailand and in Cambodia (IUCN SSC Amphibian Specialist Group 2014; Vörös et al. 2012).Although uncommon in Indonesia, it is abundant elsewhere within its range.Its primary habitat is swampy areas near streams in coastal vegetation and lowland rainforest. It can jump well, and climbs up into vegetation in addition to the forest floor. It is generally not found in cleared areas, but does occur in rubber plantations and gardens (IUCN SSC Amphibian Specialist Group 2014; Halliday 2016).

The stocky, tiny adult I. parvus toads can be brown, black, or reddish in color with pale belly, while the juveniles are bronze-brown in color, sometimes with a pink snout. Their wrinkly dorsal skin is covered with small warts.They have only partially webbed toes. Adults have a pair of symmetrical black spots on the mid-back, and ridges on their head. Males usually have a reddish throat (Iskandar, 1998). Females are somewhat larger (snout vent length 40-50 mm) than males (30-35 mm). The species name, parvus, come from the Latin word for small (IUCN SSC Amphibian Specialist Group 2014).

Shahriza et al. (2012) described the reproductive behavior of Ingerophrynus parvus in Malaysia.Tadpoles are not adapted for high-flow water, and these toads breed in low-flow pools and ephemeral puddles that occur in rainy seasons. Males call every month, but peak calling/breeding coincides with the onset of rains (July-August) when males congregate in large numbers.Females spawn clutches of eggs directly into the water source. The tadpoles are also small in size.

These toads have toxic skin.Skin extracts from 100 mg of skin cause locomotor issues, convulsions, and death to mice within 2 hours. The active toxic constituents isolated are bufadienolides; research has not yet identified the exact compound in this species. Unlike other bufonid toads, skin extracts from I. parvus did not contain serotonin products (Daly et al. 2004).

Though for years New World frogs have been plagued with deadly chytridiomycosis, incidence in Asian frogs is poorly knonw.The first case of Batrachochytrium dendrobatidis infection in Malaysia was reported in one individual Ingerophrynus parvus in 2011.The individual did not show signs of disease and this fungus has not shown signs of decimating the population or other species in the area (Vörös et al. 2012).

The skin of Ingerophrynus parvus, like most bufonid frogs, is toxic.Although skin of frogs of genus Bufo (I. parvus is formerly considered part of the Bufo group) usually contain indolic amines, such as serotonin, Daly et al. (2004), found no serotonin or its methylated products in analysis of skin extract of 18 Malaysian bufonic frogs, nor evidence of lipophilic alkaloids indicating they do not sequester dietary alkaloids from invertebrates they eat.The results of Daly et al. (2004) indicate that the skin of I. parvus containes bufadienolides (unclassified).These are neutral lipophilic compounds with an unusual C₁₇ steroidal nucleus contining an α-pyrone ring and cis-fused rings with 3β, 14β hydroxyl groups; they also often have additional oxygenation, such as epoxide, ketone, acetoxyl or more hydroxyl groups (Daly et al. 2004; Daly et al. 2008).

Ingerophrynus parvus is a species of toad in the family Bufonidae. It is found in southern Myanmar, southwestern Thailand, southwestern Cambodia, Peninsular Malaysia, and Java and Sumatra (Indonesia). Its natural habitats are primary and regenerating rainforests where it is found inhabiting streams. Breeding takes place in pools and slow-moving streams. It is common in the mainland but uncommon in Indonesia.