Caecilians: Reproduction

Summary: Now that we know about the existence of caecilians. Let’s talk about how caecilians make more caecilians! Join Kiersten as she walks us through the various ways caecilians reproduce.

 

For my hearing impaired listeners, a complete transcript of this podcast follows the show notes on Podbean.

 

Show Notes:

“The Care and Captive Breeding of the Caecilian Typhlonectes natans” by Richard Parkinson. Herpetological Bulletin, 2004, Number 88.

 

“Reproductive ecology of female caecilian amphibians (genus Ichthyophis): a baseline study” by Alexander Kupfer, Jarujin Nabhitabhata, Werner Himstedt. Boiological Journal of the Linnean Society, Vol 83, Issue 2, October 2004, pg 207-217.

*cool egg pictures in this paper

“Life history and reproduction of the neotropical caecilian Siphonops annulatus with special emphasis on parental care” by Carlos Jared, Pedro Luiz Mailho-Fontana, Simone G. S. Jared, Alexander Kupfer, Jacques Hubert Charles Delabie, Mark Wilkinson, and Marta Maria Antoniazzi. Acta Zoological, Vol 100, Issue 3, pg 292-302.

 

  Music written and performed by Katherine Camp

 

Transcript

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Kiersten - This is Ten Things I Like About…a ten minute, ten episode podcast about unknown or misunderstood wildlife.

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Welcome to Ten Things I Like About… I’m Kiersten, your host, and this is a podcast about misunderstood or unknown creatures in nature. Some we’ll find right out side our doors and some are continents away but all are fascinating. 

This podcast will focus ten, ten minute episodes on different animals and their amazing characteristics. Please join me on this extraordinary journey, you won’t regret it.

This episode continues caecilians and the seventh thing I like about these hidden gems is how they reproduce.

When it comes to reproduction most animals will reproduce in one of three ways. If you are viviparous, you give live birth to young that have developed in your uterus. If you are ovoviviparous, you give live birth to young that have developed inside eggs that are incubated in your uterus. These young are typically born with a yolk that helps nourish the young for a few days after birth. If you are oviparous, then you lay eggs that are incubated outside the body by parental warm or substrate covering. There are animals out there that reproduce in other ways, but these are the three main ways of animal reproduction.

Caecilians use two of these reproductive techniques. Of the caecilians we know of today, they are either oviparous or viviparous. 

Let’s take a look at our oviparous species’ first. Some research has been done on species in Family Ichthyophiidae. These species lay eggs and their young go through an aquatic larval stage. The species studied in this particular research was found in Thailand and individuals were observed in the wild as well as in captivity.  It was actually one of the first times caecilians in this family had been studied in situ, which means on site in their natural habitat. Ichthyophis kohtaoensis was studied for three consecutive years and researchers discovered many previously unknown behaviors. 

When we talk about reproduction in most species, it tends to revolve around certain times of the year. Very few animals are like humans and reproduce anytime of the year. Most amphibians found in tropical areas jump into breeding mode at the start of monsoon season, so one of the first questions researchers asked is whether this would be the same for caecilians. The answer they found was a bit of yes and a bit of no. Just like other amphibians, caecilians breeding season was cyclical and revolved around the rainy season. But actual mating appeared to begin at the end of the dry season before the rains came and continued into the beginning of the rainy season. Egg laying typically happened after the rainy season had already begun.

When it comes to parental care, if there is any given, it is the female only. Ichthyophis kohtaoensis does incubate eggs for approximately three months. Toward the end of the dry season, females will begin to gain weight in anticipation of remaining in a nest to guard and incubate eggs. The average number of eggs is 37 with a range of 22-58 eggs laid in one nest. Larger females tended to have larger clutch sizes. The eggs are round and clear, so you can see the developmental stages of the young inside. The pictures they included in their  scientific paper were pretty cool!

The nest site is extremely important because the larval stage of this caecilian is spent in the water. Females will chose a site with softer substrate such as sand, loose soil beneath tree roots, and sandy clay loam under grass tufts. Every nest found was between seven to nine feet from the edge of a freshwater source. The sources were varied including standing ponds and pools, slow moving brooks and rivers, and large seasonal ponds. Once the eggs hatch the young make their way into the water and are on their own. Field studies and captive observations indicate a long larval period so the chosen body of water needs to last long enough for the young to survive through this period to adulthood.

This pattern of reproduction is only one option for oviparous species. Another pattern lengthens the parental care window and has been well studied n only one species, Siphonops annulatus. Unlike Ichthyophis kohtaoensis, the young of Siphonops annulatus do not have an aquatic larval stage. When the young of this caecilian hatch they remain in the underground nest with the mother. 

Breeding season occurs about about the same time as our previous caecilian, beginning at the end of the dry season. Females gain weight at this time and lay eggs after the rainy season has begun. This is more support for the hypothesis that caecilian reproduction is cyclical and follows the seasonal changes revolving around monsoon season because this pattern has now been seen in two species from different countries. Ichthyophis kohtaoensis is found in India and Siphonops annulatus is found in Brazil. The observations reported in the study on Siphonops annulatus were collected over a period of ten years and were gathered in situ and in captivity. 

The young of Siphonops annulatus hatch after about a month but remain in the underground nest with the mother for approximately four months. This species practices dermatophagy which means they eat skin. Specifically the young eat the outer layer of their mother’s skin. Part of the weight that the female gains before egg laying includes a thickening of the outer layer of her skin. This layer bulks up with nutritious fatty lipids that the young scrape off using special baby teeth that they lose when they leave the nest. 

In captivity, young have also been seen congregating around the mother’s cloaca, which is the orifice near the end of the tail, consuming a liquid. We don’t currently know what this substance is but it may be another nutritious liquid for the young. After four months of feeding on mom in the nest, the young will emerge into the world and be on their own. Siphonops annulatus lay fewer eggs than Ichthyophis kohtaoensis and this may be due to the intensive parental care Siphonops annulatus provides.

The last form of reproduction in caecilians is live birth and we’re going to look at one of the most well studied species of viviparous caecilians, Typhlonectes natans. Hopefully you remember from previous episodes that this species is an aquatic caecilian, living their entire lives in the water. The information about the breeding behaviors of this species comes mostly from captive specimens, so this information needs to be taken with a little grain of salt because animals always act a little different in captivity than they would in the wild. These behaviors have been in several different individuals; therefore, we feel fairly comfortable saying this is what happens in the wild. 

Once again, it appears that breeding behaviors are influenced by monsoon season, but in a slightly different way than with our egg-laying species. The dry season that comes before monsoon season is when Typhlonectes natans is triggered to begin breeding. Then the females will carry their young through the following rainy season and give birth when the next dry season begins. We have no proven information why this happens, yet, but using some inference, this pattern probably provides females with more consistent access to food while they are pregnant. They carry their young for about 10 months, so it’s important to be healthy and well fed. 

The young are born in the dry season when waters are lower and calmer. This makes it easier for them to get to the surface of the water and that is important because Typhlonectes natans must surface to breath air. The young are in danger of drowning if they can’t breath air from the surface of the water. 

While they are growing inside mom, the young scrap a secretion from the mother’s uterine wall to nourish themselves. They have small fetal teeth that help them collect these nutrients. I can’t believe there is another species of caecilian that eats its mother! 

The developing young also have gills which allows the female to pass oxygen to them in utero. When the young are born, the gills are already gone or disappear within two days. After birth the young will begin to eat small, soft invertebrates within a few days and do not rely on mom for anything. 

Females are not the only one’s involved in the reproductive process. Let’s take a quick moment, because that’s all it’s going to take, to talk about what the male contributes to the next generation of caecilians. Unlike all other amphibians, that we currently know of, caecilian reproduction is internal. Most amphibians lay eggs that are fertilized after they are laid. Caecilian males have a phallodeum which is an organ that they use to pass sperm into the female through her cloaca. No other amphibian does this. With every episode I make, these caecilians become more and more fascinating.

Whether in the water or underground, the males and females twine their bodies together aligning their cloacas up with each other. Then the male inserts his phallodeum into her cloaca and passes her his sperm. A month after mating eggs are either laid or pregnancy indicators, such as weight gain and size growth, are seen.  

All of the behaviors I talked about in this episode are based on observations of just a few species of caecilians and may not apply to other species. There is so much more we have to learn about them and hopefully we’ll be able to do that in the future.

That’s all I wrote about caecilian reproduction and I trust hope you found it as fascinating as I did because it is my seventh favorite thing about the unknown amphibian.

 

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Join me next week for another thing I like about caecilians!

 

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This has been an episode of Ten Things I like About with Kiersten and Company. Original music written and performed by Katherine Camp, piano extraordinaire.