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Lithodytes lineatus, the gold-striped frog, also known as the painted ant nest frog, is a fairly common terrestrial leptodactylid widely distributed in Amazonian forests of Ecuador, Eastern Peru, Brazil, Venezuela, and the Guianas. It is the only species in its genus, but molecular studies suggest diverges that indicate a split might be due (de Sá 2014). As it lives and forages under leaf-litter, logs, and other forest cover at forest edges, pastures, and flooded savannah forest, and is mostly active nocturnally, it is not commonly noticed and little is known about its ecology (La Marca et al. 2012).
Named for the yellow stripes flanking both sides of their black back, L. lineatus has grey belly, ventrum, and hind limbs, brown throat and chest, and tan upper arms. There are distinguishing red spots on the posterior surfaces of thighs and a large red spot on the groin. Adult female L. lineatus are have a total length of 38.1 - 52.0 mm and significantly larger than adult males, who range from 34.9 - 47.0 mm (Duellman 2005, Nelson and Miller 1971; as cited in Chiachi 2013).
Gold-striped frogs are remarkable in that they frequently associate with leaf cutter ants, Atta cephalotes, in a kind of relationship never before reported in which the frogs use the burrows of ant nests as breeding sites. The relationship was first described from in Peru when synchronous calling was heard from the inside of the ant nests, advertisement calls consisting of a series of short whistles that are produced at a continuous rate of about 90 notes/minute. The notes are in three distinct harmonics at 1300, 2600 (dominant), and 3900Hz and each last about 0.12 seconds long. This relationship benefits the frogs, which receive protected brooding sites with stable temperature and humidity. To protect themselves from attack from the ants, the frogs appear to produce a chemical odor that the ants recognize; frogs and tadpoles with this odor are ignored by the ants. Granular tubercles on their backs may be the source of these protective secretions. Some experimental work showed if the odor is removed from the frogs, the ants immediately attack and kill them.
There is evidence to suggest the L. lineatus/A. cephalotes relationship is a true symbiosis, with potential mutual benefits, as frogs do not appear to eat A. cephalotes ants (although much of their diet appears to be ants of other species), and furthermore the frogs appear to eat predators plaguing the ant nests such as assassin bugs, though further research is necessary to confirm this behavior is significant (Schlüter et al. 2009).
Frog breeding occurs during the rainy season, and adults build foam nests adhered to walls above puddles inside mud ant nest burrows, or at the edge of temporary pools. Into these foam nests females lay some 100-300 unpigmented eggs, 1.5 mm in diameter. The nests house various stages of pink tadpoles (backs crested with a short light strip) where they stay about 15 days. Tadpoles start to feed several days after they leave the nest.
Gold-striped frogs turn out to have multiple protective strategies in addition to their ant mutualism. They show striking resemblance to the toxic dendrobatid frog Phyllobates fermoralis, which also has yellow dorsolateral lines and similar dorsal coloration. Juvenile L. lineatus frogs appear to have diurnal habits (unlike the adults) and Cintra et al. 2014 and Schleuter et al. 2009 suggest this is convincing Batesian mimicry of P. fermoralis giving another protective strategy. Cintra et al. 2014 also point out that L. lineatus shows deimatic “body lifting posture,” yet a third method of defense, in which the frogs lift their rear to show off aposematic coloring, and lift nictitating membrane to protect eyes.