During my studies to earn both my Bachelorās degree and my Herpetology certificate, I found the topic of reproductive strategies to be one of my favorites to go over in class.
Not only when it comes to amphibians, but to all animals. I use it a lot when doing keeper talks about snakes and which species give birth in which way!
Viviparity is fairly rare among over 8,500 known amphibian species. However:
75% of caecilians species are viviparous including the geniuses scolecomorphus, typhlonectidae, dermophiidae. Salamandra salamandra, Salamandra atra and Lyciasalamandra luschani are viviparous salamander species. And Nectophrynoides and Nimbaphrynoides occidentalis are viviparous frog species.
Viviparity refers to the reproductive strategy of motherās giving birth to live young instead of laying eggs, as in oviparity.
Viviparous amphibians retain the embryos inside their bodies and birth live young. Some species may have evolved viviparity to increase survival in their respective environments.
There is also a third reproductive strategy called Ovoviviparity. This means eggs hatch inside the mother and are born.
Most amphibian species exhibit oviparity and deposit eggs in nests or waterways where they develop and hatch. But there are some fully viviparous species that we will discuss in this article.
We will cover caecilians, salamanders, and frogs, as well as giving some explanation as to what those species are.
So if you have never heard of a caecilian before, keep reading to find out what it is!
75% of Caecilians Are Viviparous
Caecilians are elongated burrowing amphibians that lack limbs and sometimes lungs.
There are 215 Species of Caecilians according to AmphibiaWeb in December 2022
Most species are oviparous and few are viviparous. All species of caecilians reproduce using internal fertilization.
Caecilians are very elusive and secretive animals that tend to stay burrowed in mud or moist soil.
Viviparous species of caecilians secrete nutrients from the lining of their oviducts for their offspring to eat.
The larvaes teeth scrape off the skin and gain nutrients from ingesting it. Most viviparous caecilians have less offspring than oviparous species.
Scolecomorphus
Three species all from the genus Scolecomorphus are viviparous.
They belong to the Family of Scolercomorphidae, which contains another oviparous genera.
These caecilians are from countries in Africa and range from 140-460mm in length depending on the species.
Typhlonectidae
Out of the five genera and 14 species in Typhlonectidae, all are viviparous.
These species may be fully or semi-aquatic and can range between 140-750mm in length.
Gestation is typically six to seven months and 2-11 offspring are usually produced.
Dermophiidae
The Family Dermophiidae contains four genera and 15 species, all of which are viviparous.
A typical litter is between 2-7 neonates after an 11 month gestation period.
Species in the genus Geotrypete show parental care by coiling around their young.
Three Salamander Species Are Viviparous
Salamanders are slender-bodied amphibians with short limbs and tails present in larval and adult phages of development.
Most species utilize internal fertilization after a spermatophore is picked up by the female.
Some salamanders, like the axolotl, exhibit paedomorphosis; retaining larval characteristics in adulthood!
As of December 2022, AmphibiaWeb identifies 777 species of salamanders.
Salamandra salamandra
These forest dwelling salamanders range from Iran to Germany to North Africa and can be around 250mm in length.
Their parotoid gland, which secretes poison over the skin, is well hidden on the body.
The viviparous females from this species birth their larvae into bodies of water to complete their development aquatically.
Salamandra atra
This species of salamander is isolated to the Dinaric Alps, fully terrestrial, and gets around 140-150mm in length.
They have a double row of poison glands down their back and to their tail. The larvae of this viviparous species scrape the lining of the motherās uterus for nutrition.
Lyciasalamandra luschani
This species gets 110-140mm in length, has a well-defined skin fold on its neck, and contains nine subspecies.
They inhabit cool, humid caves in Turkey and have defined poison glands.
Their gestation period is 5-8 months long.
Two Frog Species Are Viviparous
The family Bufonidae contains the only two known viviparous frog species.
This family contains 640 species across 52 genera distributed worldwide excluding Australia. They include many different reproductive and life strategies.
Eleutherodactylus jasperi is an extinct ovoviviparous frog that retained eggs in the oviducts and gave birth to young froglets.Ā
Nectophrynoides
There are 13 species in this genera, and many of them are not well described. Some may be fully viviparous.
The critically endangered Nectophrynoides laticeps from Tanzania was found to have 30 eggs in a femaleās oviduct that she would raise until birth.
Nimbaphrynoides
The Nimbaphrynoides occidentalis is the only species in the genera. It is critically endangered and resides in Guinea and Liberia.
A gravid female retreats underground to complete a nine month gestation period, afterwards the froglets emerge at the start of the rainy season in April.
Benefits and Disadvantages of Viviparity
Some benefits of developing embryos in the reproductive tract of the mother come with survivorship of the offspring.
They are protected from the environment inside the motherās body and can take a longer gestation time to develop.
Eggs deposited through oviparity suffer predation and can be washed away with the environment.
The disadvantages of viviparity mainly fall on the mother as she has to dedicate a lot of energy and resources to supply her offspring with nutrients inside her body.
Sometimes females do not eat, or need to find more food than usual, and can be slowed down with a belly full of embryos.
It also delays reproducing their next litter, depending on how often the species mates.
Sources
Blackburn, D. G. (1999). Viviparity and Oviparity: Evolution and Reproductive Strategies.
Family phylogeny. AmphibiaWeb. (n.d.). Retrieved from https://amphibiaweb.org/taxonomy/AW_FamilyPhylogeny.html
Pough, F. H. (2018). Herpetology (4th ed.). Sinauer Associates, Inc., Publishers.
