I would think a face to face conversation would have been clearer too, and I am sure I could probably learn some things from you as you seem to really know your stuff about amphibians. Sorry if I seem to be nit-picking a little on these things, but being a topic I love, I tend to get carried away! I certainly would like to know more about the British amphibians you mentioned. I agree that we have to learn as much as possible about amphibians, whether they be frogs, salamanders, or caecilians, before they are gone from the face of the Earth. Considering their remarkable sensitivity to environmental changes such as pollution and climate change, there may not be any left to study within the coming generations. That’s why I get so excited when new species like these salamanders pop up, because it gives me hope that perhaps they are not all on the brink just yet.

Hopefully, we will keep finding new species of amphibians like this in order to at least offer some optimism in the face of the even faster growing list of threatened or extinct ones.

That does clear up issues, I’m sure we would have cleared up issues with nomenclature and terminology much quicker in a face to face conversation!

I’m still sure many anuran larvae do have external gills including (Rana temporaria!) though as you say not as pronounced as those of salamanders and yes these are retracted early in development.

My thesis will be looking into phenotypic plasticity during larval development in British amphibians. With specific interest in the effects of predatory chemical cues and conspecific and interspecific chemical communication.
It’s mainly looking into how exposure to threats produce different body shape and how this varies between species and if the effects can be communicated.

It’s good to discuss these things as often all I know is down to what I read, it’s always of interest and importance to get another’s information or point of view, there is always allot more to be learned.
Thanks.

One more difference that I forget to mention when discussing the difference of tadpoles versus the larvae form of Caudata. Tadpoles are completely geared toward being aquatic creatures, where that is not always the case with salamander larvae. For example, there are viviparous species which deliver their young as fully morphed, miniature adults. In these cases, the larvae complete metamorphosis within the mother’s oviduct, able to exchange gases, waste, and nutrients from the mother’s blood. Only one or two offspring out of clutches of 20-30 eggs will fully reach maturity in these instances. The rest of the eggs become nourishment for when the larvae egg sacks are depleted. The larvae of some species even cannibalize each other within the mother’s body. In the case of internally developed offspring, I would not refer to these as “tadpoles”, but rather as “larvae”, since tadpoles are actively swimming, feeding eating machines.

I guess one way you could put it is that tadpoles are larvae, but not all larvae are tadpoles. Do you see what I’m saying? Anyway, as I said, the fundamental amphibian life cycle remains the same in either case, only being somewhat complicated by those species that remain in larval form indefinitely yet possess reproductive capabilities. Even then, they could possibly fully metamorphose under certain conditions. “Tadpoles” and “larvae” represent the same basic developmental stage, and “tadpoles” would just refer to the aspects inherit in Anuran larvae exhibiting the characteristics that I have mentioned. Like I said before, I think I’m probably nit-picking a little on the distinction.

By the way, what sort of thesis topic are you writing on if you don’t mind me asking? I’d be interested to hear about it from a fellow amphibian enthusiast.

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First, let me tell you what I see are the unique attributes of “tadpoles” that differentiate them from the “larvae” of the Caudates. First of all, tadpoles have internal gills. Second, tadpoles always fully undergo metamorphosis, absorbing the tail as the frog develops into maturity. Third, tadpoles are highly specialized compared to the larval stage of Caudates and are geared toward eating a very large amount of food. Tadpoles also mature relatively quickly and thoroughly.

What I call Caudate “larvae”, are different from tadpoles in several respects. First is the presence of external, feathery gills rather than internal ones. These gills are more often than not lost upon maturity except under certain circumstances such as species which display extreme neoteny. Amphiuma are the only Caudates that display internal gills. Second, Caudate larvae retain their tails into adulthood. Third, these larvae can sometimes take extremely long times to fully reach maturity in comparison to tadpoles. The larval forms of hellbenders, for example, can take up to five years to reach full metamorphosis. Others, like the tiger salamander, only metamorphose if the ponds they live in become uninhabitable and they have to switch to a terrestrial form to survive.

This leads into the biggest difference that I see, and that is the potential for Caudates to express neoteny, or paedomorphosis, to varying degrees, essentially maintaining certain larval characteristics into reproductive adulthood. In this case, metamorphosis is stalled, not fully realized, or frozen completely. In fact, nine of the ten families of Caudata express some form of neoteny except the family Rhyacotritonidae. Four of the Caudate families are comprised fully of species that undergo paedomorphosis and retain larval characteristics well into sexual maturity. An example is the axolotles we mentioned, retaining most of their larval characteristics, yet developing reproductive organs. These species can reproduce as adults, yet retain many features of a larval form. They can turn to an adult form under very special circumstances (usually in captivity or in a laboratory), but for the most part, the metamorphosis is never completed. Tadpoles, on the other hand, always fully metamorphose.

Anyway, I guess in the end using the words “larvae” and “tadpole” are just ways to label and differentiate the same sort of intermediate form in two orders of amphibian and to highlight the things that make them unique. There are differences, but you are right and the amphibian life cycle is fundamentally always the same although there is a good amount of variety to be seen in types of fertilization, where they lay their eggs, development and characteristics of the larval forms, and so on. While most amphibians are biphasic, (meaning they go from an aquatic stage to a terrestrial stage), some amphibians lay their eggs on land, and the larval form is completed within the egg. Since the eggs are amniotic (full of their own pool of fluid) rather than the amamniotic eggs of most other amphibians (meaning the eggs rely on external water from the surroundings.), they can be laid on land without threat of desiccation. In essence, they have a completely terrestrial life cycle. Other amphibians give live birth to larvae that have developed within the mother’s body, others mouth brood, but the pattern of egg to larval form to metamorphosis to adult is essentially the same. It’s just as the life cycles of mammals shows a lot of variety, yet remains fundamentally the same. If that is what you meant, then I don’t think you have to re-write your thesis.

The research I did on the Japanese giant salamander was pertaining to investigating the effects on its habitat and possible threat posed by the introduced Chinese giant salamander (Andrias davidianus), as well as other invasive species within its ecosystem. I am thoroughly enjoying this exchange with you, Ranatemporaria, and appreciate that you are taking the time to engage me in intelligent discussion on amphibians.

I agree perhaps we are nit picking about the detail but still I thought i would straighten out a few of my points for you!

The ‘Tadpole’ form is as a pre metamorphic juvenile state referred to as larvae as per most published research papers on the subject e.g. (Relyea 2000, 2001,2002). Please could you tell me the difference between the juvenile form or ‘immature life stages’ of frogs and those of newts and salamanders? Those that have formed part of studies up till now have all taken the following developmental route.
Egg -> Larvae/Tadpole -> Metamorphosis -> Adult,
life history strategy. I would be intrigued to know of any that don’t and may need to re-write my thesis!

The tail on anurans is not externally obvious but as I wrote previous is skeletal and can be seen internally via x-ray or in dissection but non the less there. By vestigial I draw parallels with that evolutionary receded form of tail seen in humans (of which you refer) and the like.

Again as for a ‘lack of diversity’ again can I refer to my original and subsequent posts. This was a relative measure comparable to other similar taxonomic levels i.e. Cetartiodactyla which ranges from the blue whale to goats!

I think its awesome you got to work with giant Salamanders, what was the purpose of the research? I thinks its important to collect all the information we can whilst amphibians are still so plentiful.

Some interesting papers on the subject:

Vences et al 2005
Laurila et al 2002
Relyea 2000, 2001,2002

Anyway, even if they DID have tails (which they don’t display any more than humans do with our tail bones), how is that evidence of a lack of diversity, considering the presence of tails in most mammals? The three orders of amphibian (Anura, Caudata, and the caecilians) show a lot of unique attributes with regards to skeletal structure and morphology that I think should be recognized. Anurans, for example, display several unique skeletal attributes not found in other amphibians.