The Túngara frog (Engystomops pustulosus) is a species of frog in the family Leptodactylidae. It is a small nocturnal terrestrial frog found in Mexico, Central America, and the northeastern regions of South America.
The tungara frog exhibits interesting behavior in male/female interactions. Male vocalizations are critical in female mate choice, and females often prefer males who give complex mating calls at a lower frequency rather than simple calls at a higher frequency. This long distance vocalization is the primary mating behavior of tungara frogs, and it is produced by a fibrous mass in the frog’s larynx. The tungara frog may also have a mutualistic relationship with tarantulas, where tarantulas participate in predator defense while frogs protect tarantula eggs. Tungara frogs have distinct coloration which helps defend them from predators
Description
Engystomops pustulosus is a small species of terrestrial frog growing to a length of between . The tympanum is not visible and the dorsum is covered in small warts. These warts resulted in other early descriptions falsely identifying túngara frogs as a species of toad in the Bufo genus. The eyes are relatively large and protruding. Males have large, dark vocal sacs that expand when calling for females. Both males and females typically have a conspicuous white stripe that extends from the lower lip to down the throat.
Habitat and distribution
It is found from Mexico and throughout Central America and into northern South America as far east as Trinidad and Tobago, Venezuela, and possibly Guyana. Its natural habitats are subtropical or tropical dry forest, dry savanna, moist savanna, subtropical or tropical dry lowland grassland, subtropical or tropical seasonally wet or flooded lowland grassland, freshwater marshes, intermittent freshwater marshes, pastureland, heavily degraded former forest, ponds, and canals and ditches.
Ecology and diet
Engystomops pustulosus is nocturnal, emerging at night to feed on ants and termites and other small invertebrates (such as snails, beetles, flies and isopods) among the plant litter on the ground. During the breeding season, the males group together at night in temporary pools and call to attract mates. When a female chooses one of the males, amplexus occurs at the edge of the water and the male creates a foam nest in which the eggs are laid; the tadpoles develop in the water and undergo metamorphosis into juvenile frogs in about four weeks.
Mating and breeding
Mating call
The primary mating behavior of túngara frogs is long-distance mating call consisting of two distinct call components: ‘whine’ and ‘chuck’. Males produce a call that consists of a whine, and can also add up to seven short chuck sounds to their mating call. A call consisting of both a whine and a chuck is considered a complex call. The chuck portion of the call is produced by vibrations of a fibrous mass suspended near the frog's larynx, with larger masses allowing production of more chucks per whine. Whine is a long, frequency-modulated sound with five harmonics, fundamental frequency sweeping from 900 Hz to 400 Hz, dominant frequency of about 700 Hz, and duration of about 300 ms. Chuck is a short, high amplitude burst of sound with 15 harmonics, fundamental frequency of about 200 Hz, dominant frequency of about 2500 Hz, 90% of its energy above 1500 Hz, and duration of about 45 ms. With these components, male túngara frogs can produce two types of calls: simple call, consisting only of whine, and complex call, consisting of whine immediately followed by up to six or seven chucks. Whine induces female phonotaxis and contributes to species recognition, while chuck increases the call’s attractiveness in mating.
The main organ responsible for producing sound in túngara frogs is larynx supported by its fibrous mass hanging from the vocal cords and projecting from the larynx into the bronchi. As the trunk muscles around the lungs contract, the expelled air pushes through the larynx and vibrates the vocal cords/folds and the larynx, producing the sound. Air enters the buccal cavity, passes through the vocal slits, and inflates the vocal sac. The inflation of vocal sac is also known to serve as a visual cue to receivers. Male túngara frogs produce chuck through their fibrous mass, and their fibrous mass is larger than other species and populations that do not produce chuck. Also, surgical excision of the fibrous mass inhibits the production of chuck despite the frog’s attempt to produce complex call.