The túngara frog (''Engystomops pustulosus'') is a species of
frog
A frog is any member of a diverse and largely semiaquatic group of short-bodied, tailless amphibian vertebrates composing the order (biology), order Anura (coming from the Ancient Greek , literally 'without tail'). Frog species with rough ski ...
in the family
Leptodactylidae
The southern frogs form the Leptodactylidae, a name that comes from Greek meaning a bird or other animal having slender toes. They are a diverse family of frogs that most likely diverged from other hyloids during the Cretaceous. The family has u ...
.
It is a small
nocturnal
Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite.
Nocturnal creatur ...
terrestrial frog found in Mexico,
Central America
Central America is a subregion of North America. Its political boundaries are defined as bordering Mexico to the north, Colombia to the southeast, the Caribbean to the east, and the Pacific Ocean to the southwest. Central America is usually ...
, and the northeastern regions of
South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...
.
The túngara 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 túngara frogs, and it is produced by a fibrous mass in the frog's larynx. The túngara frog may also have a mutualistic relationship with tarantulas, where tarantulas participate in predator defense while frogs protect tarantula eggs. Túngara 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
Warts are non-cancerous viral growths usually occurring on the hands and feet but which can also affect other locations, such as the genitals or face. One or many warts may appear. They are distinguished from cancerous tumors as they are caus ...
. These warts resulted in other early descriptions falsely identifying túngara frogs as a species of
toad
Toad (also known as a hoptoad) is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands.
In popular culture (folk taxonomy ...
in the ''
Bufo
''Bufo'' is a genus of true toads in the amphibian family Bufonidae. As traditionally defined, it was a wastebasket genus containing a large number of toads from much of the world but following taxonomic reviews most of these have been moved to ...
'' 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
habitat
In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
s are
subtropical or tropical dry forest
The tropical and subtropical dry broadleaf forest is a habitat type defined by the World Wide Fund for Nature and is located at tropical and subtropical latitudes. Though these forests occur in climates that are warm year-round, and may receive ...
, dry
savanna
A savanna or savannah is a mixed woodland-grassland (i.e. grassy woodland) biome and ecosystem characterised by the trees being sufficiently widely spaced so that the canopy does not close. The open canopy allows sufficient light to reach th ...
, moist savanna,
subtropical or tropical dry lowland grassland, subtropical or tropical seasonally wet or flooded lowland grassland, freshwater
marsh
In ecology, a marsh is a wetland that is dominated by herbaceous plants rather than by woody plants.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p More in genera ...
es, intermittent freshwater marshes, pastureland, heavily degraded former forest,
pond
A pond is a small, still, land-based body of water formed by pooling inside a depression (geology), depression, either naturally or artificiality, artificially. A pond is smaller than a lake and there are no official criteria distinguishing ...
s, and
canal
Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface ...
s and ditches.
Ecology and diet

''Engystomops pustulosus'' is
nocturnal
Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite.
Nocturnal creatur ...
, emerging at night to feed on
ant
Ants are Eusociality, eusocial insects of the Family (biology), family Formicidae and, along with the related wasps and bees, belong to the Taxonomy (biology), order Hymenoptera. Ants evolved from Vespoidea, vespoid wasp ancestors in the Cre ...
s and
termite
Termites are a group of detritivore, detritophagous Eusociality, eusocial cockroaches which consume a variety of Detritus, decaying plant material, generally in the form of wood, Plant litter, leaf litter, and Humus, soil humus. They are dist ...
s and other small invertebrates (such as
snail
A snail is a shelled gastropod. The name is most often applied to land snails, terrestrial molluscs, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class Gas ...
s,
beetle
Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
s,
flies
Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwin ...
and
isopod
Isopoda is an Order (biology), order of crustaceans. Members of this group are called isopods and include both Aquatic animal, aquatic species and Terrestrial animal, terrestrial species such as woodlice. All have rigid, segmented exoskeletons ...
s) among the
plant litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituent ...
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
Amplexus (Latin "embrace") is a type of Mating, mating behavior exhibited by some External fertilization, externally fertilizing species (chiefly amphibians, Amphipoda, amphipods, and horseshoe crabs) in which a male grasps a female with his fro ...
occurs at the edge of the water and the male creates a
foam nest in which the eggs are laid; the
tadpole
A tadpole or polliwog (also spelled pollywog) is the Larva, larval stage in the biological life cycle of an amphibian. Most tadpoles are fully Aquatic animal, aquatic, though some species of amphibians have tadpoles that are terrestrial animal, ...
s develop in the water and undergo
metamorphosis
Metamorphosis is a biological process by which an animal physically develops including birth transformation or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and different ...
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 mating call is the auditory signal used by animals to attract mates. It can occur in males or females, but literature is abundantly favored toward researching mating calls in females. In addition, mating calls are often the subject of mate choi ...
. 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
The larynx (), commonly called the voice box, is an organ (anatomy), organ in the top of the neck involved in breathing, producing sound and protecting the trachea against food aspiration. The opening of larynx into pharynx known as the laryngeal ...
, 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.[Ryan, Michael, and Monica Guerra. (2014). ''The Mechanism of Sound Production in Tungara Frogs and Its Role in Sexual Selection and Speciation''. Current Opinion in Neurobiology 28: 54-59.]
Mate choice
Female preferences for calls play a significant role in túngara frog mating. They favor complex calls over simple calls, low frequency chucks over high frequency chucks, and conspecific whine over heterospecific whine. Females prefer the mating call of frogs who produce chucks with lower frequencies. If a female finds a male's call attractive, she will use the call, as well as ripples in the water caused by its production, to locate her new mate.
Female choice for complex calls can be explained by the tuning of the túngara frog's inner ear organs: the amphibian papilla and the basilar papilla. The frequency that the basilar papilla is most sensitive to is 2130 Hz, and the chuck’s dominant frequency is about 2500 Hz. The smaller the frequency difference between the male's chuck frequency and the tuning of the basilar papilla, the greater the neural excitation of the female. Thus, females prefer the lower frequency chucks that are closer to the tuning frequency of the basilar papilla.
Female choice for low frequency chucks comes from female's preference for larger males providing reproductive benefit. The size difference between the mates determines the fertilization rate in that decrease in the size difference leads to decrease in the number of unfertilized eggs and increase in fertilization rate. Due to the tendency of female túngara being larger than male túngara frogs, larger males lessen the size gap with females and benefit the fertilization. And since larger males have larger larynxes, they produce lower frequency of sound (chuck and whine). Consequently, strong sexual dimorphism can be observed in larynx size. Until about 16 mm snout-to-vent length, females and males have larynges of about the same size. However, above this point, males show strong positive allometric growth in larynx size until the plateau of growth at about 24 mm snout-to-vent length, around the time of the male's first call in the field. This shows that male reproductive behavior is triggered at the full development of the larynx.
Female choice for conspecific whine comes from the lack of prediction between phylogenetic similarity of the túngara frog species and acoustic similarity of their calls. Also, shared common ancestry is suggested to lead to shared auditory and neural responses. Compared to the former female choice, female choice for conspecific whine has less significance due to the lack of overlap between the habitat of túngara frogs and the habitat of other ''Physalaemus'' species, decreasing the instances of avoiding the calls of close relatives.
The phonotaxis experiment endorses the female call preference for complex calls and low frequency chucks. In terms of female choice for complex calls, the experiment is set up in a way that a female is placed equidistant between two speakers broadcasting series of test calls. The results show that females predominantly prefer a whine with one chuck to a simple whine by more than fivefold. In terms of female choice for low frequency chucks, the experiment is set up in a way that a female is given identical whines, but the single chuck following the whine is in either low or high frequency. The results show that females prefer whine followed by low frequency chuck. Additionally, females prefer low frequency whine to high frequency whine.
The test with reconstructed ancestral cells endorses the female call preference for conspecific whine. The results show that females give strongest response to calls of phylogenetically closest species, indicating the more significant influence of evolutionary history than acoustic similarity.
Recent research suggests that sexual calls from the males are influenced by their dietary conditions. Female frogs responded to unfed males calls less as time unfed increased.
Male/male interactions
Despite the benefit of satisfying the female choice and increasing mating success, complex calls also follow with a cost of increased risk of predation and parasitism because frog-eating bats, ''Trachops cirrhosus'', and blood-sucking flies, ''Corethrella spp.'', prefer complex calls to simple calls.Like females, these predators prefer complex calls and will use them to locate and prey upon male túngara frogs; thus, males have been found to alternate between complex and simple calls depending on the situation.[Page, R.A., Bernal, X.E. 2006. ''Túngara frogs''. Current Biology. 23:R979-980] Males produce complex calls more often when there are other calling males nearby, forming what is known as a chorus. Males that use such calling strategies are able to maximize the possibility of finding a mate and minimize predation risk.[Baugh, A.T, Ryan, M.J. 2010. ''The relative value of call embellishment in túngara frogs''. Behavioral Ecological Sociobiology. 65:359-367.]
Therefore, the males must find a strategy that resolves the conflict between natural selection and sexual selection. While portraying a trait that increases its attractiveness, the male must also remain inconspicuous through strategic variance of call complexity. When males are alone, they produce mostly simple calls, but when they are in choruses, they increase their call complexity and produce complex calls.
Research suggests the relationship between the chorus size and the costs and benefits of frog chorusing behavior. The benefit of frog chorusing behavior is increased in larger chorus size because increase of chorus size leads to increase of operational sex ratio, probability of mating, and decrease of predation risk. While predation rate and chorus size do not have a correlation, predation risk and chorus size do have correlation. The cost of frog chorusing behavior is increased in smaller chorus size, as shown in the negative correlation between predation risk and chorus size. The tendency of acoustically orienting predators to attack choruses influences the individual's predation risk in a way that when the predator appears in the site of chorusing, the individual has a higher chance of getting attacked when there are not as many frogs in the site. The cost-benefit model of the frog chorusing behavior suggests the influence of the asymmetric benefits related to male size and behavior on the size of male túngara frogs in terms of joining the choruses.
Reproduction
As male túngara frogs gather in choruses in the breeding site and call their mates, females move smoothly through the crowd of males and choose their mate through physical contact. The male clasping the female from the top, they remain in the state of amplexus for up to several hours. When mating, the male frog centers himself atop the female to do a rhythmic mixing of a foam-producing solvent released by the female to generate a floating foam nest.[Dalgetty L. and M. W. Kennedy. (2010)]
Building a home from foam - túngara frog foam nest architecture and three-phase construction process.
''Biol. Lett.'' 6(3) 293-296. The nests are resistant bio-foams that protect the fertilized eggs. After about four days, the tadpoles leave and the nest degrades but otherwise can last for up to two weeks.
Female túngara frogs also exhibit elicitation behaviors that mainly serve to cause a potential mate to increase its sexual display intensity. Among all repeatable and noticeable locomotive behaviors that females exhibit, behaviors in which females clearly move closer to or farther from males are known as approach/retreat (AR) behaviors, while behaviors in which females do not move closer or farther are known as nonapproach/retreat (NAR) behaviors. Specifically, behaviors, elicitation behaviors are NAR behaviors that induce increase of number of chucks from males. Their primary role is manipulating male display, not acquiring mate. Elicitation behaviors vary with male chorus size, being more common in low density choruses than high density choruses due to its main purpose of producing more chucks. In high density choruses, increased production of chucks would not provide as much benefit than in low density choruses.
Relationships with other organisms
It has been reported that the frog may have a mutualistic relationship with tarantula
Tarantulas comprise a group of large and often hairy spiders of the family Theraphosidae. , 1,100 species have been identified, with 166 genera. The term "tarantula" is usually used to describe members of the family Theraphosidae, although ...
s of the genus ''Aphonopelma
''Aphonopelma'' is a genus of tarantulas native to the Americas. It includes nearly all the North American tarantula species north of Mexico and a considerable percentage of the tarantula species that range into Central America. Most are fairly ...
'' in Mexico. As observed in microhylid
The Microhylidae, commonly known as narrow-mouthed frogs, are a geographically widespread family of frogs. The 683 species are in 57 genera and 11 subfamilies.
Evolution
A molecular phylogenetic study by van der Meijden, et al. (2007) has estima ...
frog '' Chiasmocleis ventrimaculata'' and tarantula ''Xenesthis immanis
''Xenesthis immanis'', the Colombian lesser black tarantula,''Common Names of Arachnids'', American Arachnological Society (2003) is a terrestrial bird spider (tarantula) found in Colombia, Venezuela, and Peru. It is a relatively large spider wit ...
,'' the spider may protect the frog from predators while the frog protects the spider's eggs from ants, an interaction that may occur with other microhylids as well as the túngara frog, which is a leptodactyloid.
Protective coloration and behavior
Some of the main predators of túngara frogs include bat (''Trachops cirrhosus''), frog (''Leptodactylus pentadactylus''), opossum (''Philander opossum''), and crab (''Potamocarcinus richmondia''). In order to protect themselves from the predators, they develop protective coloration depending on the region of the habitat. Túngara frogs have two distinct color patterns: unstriped pattern and striped pattern. The frequency of color patterns differs along the urbanization gradient of the region. Increased urbanization has affected anti-predator coloration of túngara frogs, especially leading to increase of striped individuals. Striped frogs are more abundant in urban areas than in forest areas. Specifically, striped frogs are more likely to be abundant in areas than forest areas where avian predation is prevalent. In addition, frogs in forest areas have lower numbers of attacks by birds compared to frogs in urban areas, but predation rates are similar for unstriped and striped frogs. The research also suggests the factors other than urbanization should be considered in understanding the change of coloration dynamics in region, such as different predator communities and predation pressure. The protective coloration will continuously change its frequency and pattern depending on the various factors.
Conservation
Within the extinction risk categories assigned by the IUCN Red List
The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...
, Engystomops pustulosus is listed as “Least Concern
A least-concern species is a species that has been evaluated and categorized by the International Union for Conservation of Nature (IUCN) as not being a focus of wildlife conservation because the specific species is still plentiful in the wil ...
”. Although its IUCN
The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...
status seems to lessen the concern of population conservation of túngara frogs, 43% of species are experiencing decline, which suggests this frog may be threatened in the near future. The major stressors of amphibian declines include the following: habitat loss/degradation, pollution, climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
, and invasive species.
Among all causes, habitat loss/degradation and pollution are known to be the most important. These causes also show cooccurrence in that intensified agricultural and urbanized landscape lead to both habitat change and increased pollutant release. However, the specific effects of these causes on amphibians, especially their health, are largely unknown.
Some research suggests the negative impact of agricultural sites on túngara frog health, displayed by decreased egg number, reduced hatching success, and undersized/smaller body size and male secondary sexual characteristics. Such findings in research significantly relates to the conservation of amphibians, since lower reproduction is likely to correlate with an accelerated population decline.
References
External links
Smithsonian: The Tungara Frog's Mating Call Attracts Predators
National Geographic: How Female Frogs Get Tricked Into Choosing An "Ugly" Mate
{{Taxonbar, from=Q1895136
pustulosus
Frogs of North America
Frogs of South America
Amphibians of Central America
Amphibians of Belize
Amphibians of Colombia
Amphibians of Costa Rica
Amphibians of El Salvador
Amphibians of Guatemala
Amphibians of Guyana
Amphibians of Honduras
Amphibians of Mexico
Amphibians of Nicaragua
Amphibians of Panama
Amphibians of Trinidad and Tobago
Amphibians of Venezuela
Amphibians described in 1864
Taxa named by Edward Drinker Cope
Taxonomy articles created by Polbot