Image: A female gastric-brooding frog’s young develop within her stomach, and she gives birth, or regurgitates the froglets, through the mouth.
Perhaps the Surinam toad doesn’t employ the weirdest mode of reproduction amongst the frogs and toads. The female gastric-brooding frog or the platypus frog (Rheobatrachus spp.) of Australia “brood[s her] young within [her] stomach and give[s] birth through the mouth.” It’s definitely a unique mode of reproduction.
Sadly, however, gastric-brooding frogs are probably extinct. Their unusual mode of reproduction is known only from some photographs or written accounts of observations, so the chance exists that no other living human will be able to witness one of nature’s most extraordinary events. I don’t believe that video exists showing the female frogs give birth through the mouth. However, if you know of video, then please share the information.
There were two known species of gastric-brooding frogs — Rheobatrachus silus, or the Southern gastric-brooding frog, and Rheobatrachus vitellinus, or the Eungella gastric-brooding frog — and both species are presumed extinct. It is unknown why these frogs disappeared but chytridiomycosis, in addition to habitat destruction, is suspected. Via the International Union for Conservation of Nature (IUCN):
The reason(s) for the disappearance of this species remains unknown (Tyler and Davies 1985b). Populations were present in logged catchments between 1972 and 1979. Although the species persisted in the streams during these activities, the effects of timber harvesting on this aquatic species were never investigated. Its habitat is currently threatened by feral pigs, invasion of weeds (especially mistflower Ageratina riparia), and altered flow and water quality due to upstream disturbances (Hines, Mahony and McDonald 1999). However, from what is known from similar declines and disappearances elsewhere in the world, the disease chytridiomycosis must be suspected.
However, a new, efficient automated system, which seems to be exceptionally accurate, may locate any gastric-brooding frogs that might still be in existence by listening for them. Via ABC Science Online:
Citizen science and computer software are being harnessed as a low-cost way of tracking Australian native bird species in order to monitor environmental change.
The Queensland University of Technology software is also being used on the frontline in the battle to stop cane toads marching on to Groote Eylandt in the Northern Territory.
The program uses automatic acoustic sensors, voice recognition technology and expert birdwatchers to reduce the number of hours ecologists have to spend in the field observing wildlife.
Researcher Jason Wimmer, a PhD student, says experiments show the automatic system is actually more effective in capturing the presence or absence of birds than standard observation.
Under the project, sensors are placed in the bush to record environmental sounds that are then transmitted to an online digital library.
To overcome the need to sit through hours of recordings to listen for bird sounds, Wimmer and his team developed a software program to filter the audio and identify potential bird noises.
. . .
Wimmer says the potential of the automatic system was highlighted by a 2 am recording of the call of a rarely sighted species, Lewin’s Rail (Lewinia pectoralis).
“That is just one example of the impact this system can have,” he says.
The system is also going to be used to find the Gastric Brooding Frog, a native frog that has not been seen for 20 years with sensors to be placed in the Conondale Range, north-west of Brisbane.
Wimmer says the technology is also helping protect native quolls on Groote Eylandt from eating cane toads. The island is currently free of cane toads.
“We’ve put in sensors as an early-warning system for cane toads,” he says. “The sensors are all 3G (mobile phone)-based and timed to record and analyse data automatically.”
The sensor turns on every 30 minutes and if it hears the distinctive canetoad calls is programmed to send SMS alerts to various people.
Continue reading this article at ABC Science Online.
To prevent digestive juices from destroying the eggs and tadpoles, both the eggs and tadpoles produced or were associated with a “substance [that] had the ability to turn off the production of hydrochloric acid in the [frog's] stomach.” After some time, developing within their mother’s stomach, fully-formed froglets emerge from the mother’s mouth (though some accounts note that one of the species gave birth to tadpoles — not fully-formed froglets). More on the reproductive habits of Rheobatrachus silus via the IUCN:
Females brood young within the stomach and give birth through the mouth (Tyler and Carter 1982). Fertilized eggs or early stage larvae are presumably swallowed by the female and complete their development in the stomach (Tyler and Carter 1982). The number of eggs in gravid females (approximately 40) exceeds the number of juveniles found to occur in the stomach (21-26) (Tyler 1989). It is not known whether or not the excess eggs are digested by the female or whether or not they are simply not swallowed (Tyler 1989). The production of hydrochloric acid in the stomach of the female ceases during brooding (Tyler et al. 1983). Tadpoles develop in a manner similar to the aquatic tadpoles of other species though, as they feed off egg yolk, the labial teeth are absent and the intestines form at a later stage of development (Tyler 1989). After 6-7 weeks the females give birth to up to 25 young (Tyler and Davies 1983a). Young emerge from the female’s mouth as fully formed frogs and after four days the digestive tract returns to normal and the female recommences feeding (Tyler and Davies 1983b). Ingram (1983) reported minimum brooding periods from two individuals of 36 and 43 days and suggested that the duration was such that females were unlikely to breed twice in one season.
More on the reproductive habits of Rheobatrachus vitellinus via the IUCN:
It is an aquatic species largely restricted to the shallow section of fast-flowing creeks and streams in rainforest. It is one of only two known species to brood its offspring within its stomach. Females deposited their eggs, and then swallowed them. While in the stomach, tadpoles excreted some form of enzyme that inhibited the female’s gastric digestion, and then proceded to develop into fully formed froglets. The froglets were then regurgitated through the female’s mouth.
More via Vitt and Caldwell (2009):
In the gastric brooding frogs, Rheobatrachus silus and Rheobatrachus vitellinus, brooding of eggs and/or larvae occurs in the stomach of the female; in one species, froglets emerge after metamorphosis, whereas in the other species, tadpoles are released by the female. Development in those frogs is supported entirely by yolk contained in the eggs (Crump, 1995; McDonald and Tyler, 1984). In contrast to Rhinoderma rufum, male Rhinoderma darwinii brood their tadpoles in their vocal sacs until metamorphosis occurs (Crump, 1995).
I couldn’t find information on whether the females of either species of gastric-brooding frogs stop feeding during gestation. However, it seems that more eggs were typically produced and swallowed than the number of froglets that were actually hatched or regurgitated by the female, so either the females digested some or all of the eggs, or the tadpoles and froglets consumed some or all of the unfertilized eggs while in the stomach, or perhaps some combination of both behaviors existed. There must have been some mechanism in place to utilize or dispose of unfertilized or bad eggs. Perhaps, the tadpoles practiced cannibalization as well. Tadpoles are known to practice cannibalism.
Video (this video plays automatically): In this video, a Southern gastric-brooding frog swims about a tank, and there’s a still image showing a froglet in adult’s mouth. Via ARKive
Image of Darwin’s Frog via
However, one species of frog, still in existence, uses a somewhat similar mode of reproduction to the gastric-brooding frogs of Australia. Darwin’s frog (Rhinoderma darwinii) is a species that’s “endemic to the austral forest of Chile and Argentina.” The species is considered vulnerable, and its population is in decline. Via the IUCN:
Recent surveys within the range of Rhinoderma darwinii in Chile reveal that some populations (including those in national parks and other preserved areas) have disappeared entirely (M. Crump and A. Veloso pers. comm.). In other areas, the density of frogs is much lower than 10 or 20 years ago (M. Crump pers. comm.). Forestry operations have destroyed large areas where northern populations were found. However, it was still abundant in at least some southern Chilean localities in 2003; indeed, it appears that the species reaches its highest densities in regions of the Archipelago, where habitat disturbance is minimal (M. Crump pers. comm.). In Argentina, this is a scarce species and appears to have declined at one site (Puerto Blest, Río Negro Province) during the past 50 years.
. . .
In the north, the main threats are drought and pine forestry, while in the south it is clear-cutting of forest. Declines that have taken place in suitable habitat could be the result of other threats, such as climate change or disease (possibly chytridiomycosis, although this normally impacts species that are associated with water, and it has not previously been reported from Chile).
Instead of gestation taking place within the female’s stomach, as with the gastric-brooding frogs, the male Darwin’s frog “ingest[s] the eggs and incubate[s] them in vocal sacs.” Six weeks later, the male frog literally gives birth to fully-formed froglets through the mouth (though Rhinoderma rufum releases tadpoles, instead of froglets, from its vocal sacs) — making the male frogs of this species “the only other member of the animal kingdom that exhibits anything close [to] the seahorse [and their kin], where the male carries the babies in a brood pouch.” More on Rhinoderma rufum via Wikipedia:
This species of frog exhibits a highly unusual form of parental care in that the tadpoles spend part of their life developing in the vocal sac of their father, where they ‘hitch a ride’ to a pool of water in their father’s vocal sac where they complete their development from the tadpole to the frog form.
Video: In this video, it’s possible to see the movement of tadpoles within the vocal sacs of the Darwin’s frog.
Video (this video plays automatically): A male Darwin’s frog releases fully-formed froglets from his vocal sac. Via the BBC.