Hylodes asper, or the Brazilian torrent frog, is a species of frogs in the Hylodidae family. It is endemic to the Rio de Janeiro and São Paulo states in southerastern Brazil. Living in a high-noise environment, the species uses "semaphoring" to supplement acoustic signalling.
Hylodes asper are diurnal. Males use both visual and acoustic signalling to attract females and to maintain their territories. "Foot-flagging" is the most distinctive visual display, usually performed while calling. In foot-flagging, the raises one hind limb and extends it up and back, exposing the silvery colour of the dorsal surfaces of toes and toe fringes.
Male Hylodes asper have been observed to construct an underwater chamber, apparently for use as a nest for reproduction.
Hylodes asper is generally common, but local declines have been reported. The most significant threats to this species are the effects of tourism and water pollution, although it generally lives in steep terrain with little development.
This species occurs in southeastern Brazil, in the states of Rio de Janeiro, São Paulo, and Paraná. It is found in both primary and secondary forest, along forest streams and rivers, on steep hillsides up to 1,200 m above sea level (IUCN 2006).
Hylodes asper lives along forest streams and rivers. For territorial displays in this high-noise environment, the frog uses a kind of semaphoring (slowly raising and waving a rear leg, one at a time), in addition to calling. This behavior is known as foot-flagging, since the slow waving of the frog's large rear foot resembles a flag waving.