Tetrapod Zoology

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On Monday 7th December the Zoological Society of London (ZSL) hosted the one-off event ‘The Secret World of Naked Snakes’ (part of the ZSL’s ‘communicating science’ series): a whole meeting devoted entirely to those bizarre, poorly known, limbless, worm-like amphibians, the caecilians. The meeting was attended by over 100 people, which really isn’t bad going, especially when some of the organisers expressed fears that the event would only be attended by (to quote David Gower) “A handful of caecilian freaks”.

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Ken Livingstone [shown here] – former Mayor of London and well-known amphibian enthusiast – chaired the meeting, and a good job he did too. Mr Livingstone has shown notable commitment to conservation and to educational outreach programmes involving the ZSL (he’s a former member of the ZSL Council). He even got married in the grounds of the zoo in September of this year. He explained how – like so many people interested in amphibians – he read about caecilians at an early age, but has never seen a live one! (I’m in the fortunate position of knowing people who own pet ones).

The talks kicked off with Mark Wilkinson’s introduction to the group. As shown by select quotes from Linnaeus, John Edward Gray and Otto Fuhrmann, biologists have long complained about the dearth of our knowledge on caecilians (Linnaeus said that amphibian experts know very little, and what they do know is wrong). These same biologists have also long complained about uncertainties over the affinities of these animals within Tetrapoda (remember that caecilians were once regarded as snakes). While a dearth of knowledge is to be expected for such a cryptic group, poorly recorded locality data and a poor and sometimes sloppy appreciation of variation have combined to make caecilian systematics extremely confused. The enormous contribution made by Edward H. Taylor’s numerous publications definitely fuelled a rise in scientific interest in the group, but Taylor was a rampant splitter and many of his taxonomic decisions were faulty. He sometimes named males and females of the same species as distinct taxa, while Nectocaecilia cooperi – regarded as distinct because of its proportionally broad head and narrow body – was named for a captive specimen of Typhlonectes natans that was only wide-headed and narrow-bodied because it was chronically malnourished [part of Wilkinson's talk shown below].

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It is – I hope! – well known among zoologists that huge numbers of new anuran and caudate species have been named in recent years. Yet, Wilkinson noted, the number of new caecilian species hasn’t risen much at all. It may well be that there aren’t as many new caecilians to name as there are anurans and caudates, but even so it’s possible that the actual number of species might be twice as high as the currently recognised count (of c. 180). Wilkinson finished his talk by looking at how caecilians might be allied to other amphibians: even crown-caecilians must have diverged way back in the Triassic (Roelants et al. 2007) or even much earlier (Marjanović & Laurin 2007). Fossil caecilians don’t amount to much, and even if the limbed, Early Jurassic Eocaecilia really is a relative of caecilians proper, it may not have been such a big deal given that molecular clock estimates indicate the presence of several lineages of crown-caecilians at the same time (Roelants et al. 2007).

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David Gower presented the second talk of the meeting: ‘Recent discoveries – a golden age for caecilian biology?’. Various new notable caecilian species have been named in recent years: examples include the giant lungless typhlonectid Atretochoana eiselti (named in 1968, but only recognised as truly novel and given its own genus in 1995), and the tiny, terrestrial lungless caeciliid Caecilita iwokramae (only just described by Wake & Donnelly (2009): its head is shown in the adjacent images. Scale bar = 1 mm!). And new discoveries, like rotational feeding, maternal dermatophagy, protrusible eyes and hydrostatic locomotion, have brought caecilians to the widespread attention of biologists. But, Gower asked, are we really in a ‘golden age’ of new insight and discovery? A graph plotting all 1000 or so caecilian-specific publications over time showed that scientific interest in caecilians rose sharply as a result of Edward Taylor’s work, such that about half of all caecilian research has been published since the 1980s. But the graph’s curve has not risen exponentially over the last 10-15 years and, if anything, research output has levelled off recently.

What might make the modern age a ‘golden’ one is the breadth and depth of the sort of research being done, and Gower emphasised the excellent and extensive work being done on the group in India, the only place in the world with its own dedicated ‘endemic’ community of caecilian specialists (one of which is a nun). More than half of all Indian caecilian species have been named in the past ten years, and these represent animals that span a good deal of both ecological and morphological diversity within the clade (viviparity is now known in Indian caecilians, for example). Indian workers have published chromosomal studies of caecilians, have analysed cranial ontogeny, and have even produced wonderfully illustrated photographic field guides on the group. Studies show that caecilians are very abundant in some Indian habitats: Gower discussed a site at the edge of a tea plantation where more than 60 caecilians were dug up in the space of an hour, making them the most abundant vertebrates in the habitat. This provides further support for the idea that caecilians may have an important impact on ‘soil ecosystem engineers’ like termites and earthworms (see Jones et al. 2006), that they play a role in the maintenance of some ecosystems, and that their presence is very likely an indicator of ecosystem health.

In conclusion, more is being learnt about caecilians than was the case in the past, and the many fantastic discoveries being made about these animals are the subject of ‘targeted’ research; they are not merely opportunistic as was often the case before.

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David finished his talk by showing a few movies ‘from the field’. Judging from these movies, Mark Wilkinson is evidently some kind of caecilian-hunting guru genius: with just two lazy, shallow strokes of a spade, he was able to discover two caecilians in their native habitat. In another movie, David’s progress at the edge of a stream (he was also digging for caecilians) proved so offensive to the local children that they tried to remove his spade and do a better job themselves. David also showed a very cool photo of a very ambitious caecilian, gaping its jaws wide while trying to bite a giant earthworm. I’d like to have known the outcome of the encounter but forgot to ask (though remember that caecilians don’t try and swallow big prey whole: instead they spin about their long axis and tear the prey to bits (see Measey & Herrel 2006) [adjacent photo, from Measey & Herrel (2006) shows Schistometopum thomense (the yellow animal) attacking an earthworm. The caecilian is grabbing the worm and has twisted it about its long axis]).

And that’s not all. More to come in part II, including some stuff specifically relevant to Tet Zoo’s readership…

For previous Tet Zoo articles on caecilians, please see…

Refs – -

Jones, D. T., Loader, S. P. & Gower, D. J. 2006. Trophic ecology of east African caecilians (Amphibia: Gymnophiona), and their impact on forest soil invertebrates. Journal of Zoology 268, 117-126.

Marjanović, D. & Laurin, M. 2007. Fossils, molecules, divergence times, and the origin of lissamphibians. Systematic Biology 56, 369-388.

Measey, G. J. & Herrel, A. 2006. Rotational feeding in caecilians: putting a spin on the evolution of cranial design. Biology Letters 2, 485-487.

Roelants, K., Gower, D. J., Wilkinson, M., Loader, S. P., Biju, S. D., Guillaume, K., Moriau, L. & Bossuyt, F. 2007. Global patterns of diversification in the history of modern amphibians. Proceedings of the National Academy Sciences, USA 104, 887-892.

Wake, M. H. & Donnelly, M. A. 2009. A new lungless caecilian (Amphibia: Gymnophiona) from Guyana. Proceedings of the Royal Society B doi: 10.1098/rspb.2009.1662

Comments

  1. #1 Dartian
    December 10, 2009

    The meeting was attended by over 100 people, which really isn’t bad going

    Indeed not. In fact, it’s quite an impressive attendance given the subject matter. Kudos to ZSL for successfully putting such a meeting together.

    Furhmann

    Fuhrmann, surely?

    stuff specifically relevant to Tet Zoo’s readership

    Ooh, a cliffhanger ending! Those italics got me on the edge of my seat.

  2. #2 David Marjanović
    December 10, 2009

    Wilkinson finished his talk by looking at how caecilians might be allied to other amphibians: they must have diverged way back in the Triassic (Roelants et al. 2007) or even much earlier (Marjanović & Laurin 2007).

    :-) It’s nice that you cite us, but… Roelants et al. (2007) found a DEVONIAN date of origin of Lissamphibia ( = divergence between Gymnophiona and Batrachia), and we found a Late or perhaps Middle Permian one because we used more realistic calibration points.

    (Caecilians burrowing through the shores onto which Ichthyostega heaves itself! Imagine!)

    even if the limbed, Early Jurassic Eocaecilia really is a relative of caecilians proper

    I absolutely can’t see what else it could be. It’s very clearly outside the crown group, and so is the Early Cretaceous Rubricacaecilia, but it’s still obviously closer to crown caecilians than to anything else.

    Further fossil caecilians: a few Cenomanian, Maastrichtian, and Thanetian vertebrae which could belong to the crown group.

    Gower discussed a site at the edge of a tea plantation where more than 60 caecilians were dug up in the space of an hour, making them the most abundant vertebrates in the habitat.

    :-o

    remember that caecilians don’t try and swallow big prey whole

    I thought Microcaecilia did? Or was that just inferred and not observed?

    Fuhrmann, surely?

    Of course. No rh in German (except in Greek words, in which a vowel follows it); silent h lengthens the preceding vowel.

  3. #3 Darren Naish
    December 10, 2009

    Thanks for comments. Ah, yes, Roelants et al. (2007) show the gymnophionan lineage extending all the way to the Devonian as you state, but they posit a Triassic date for the emergence of the crown. Still, point taken :)

    As for Fuhrmann, sorry for silly typo.

  4. #4 Dartian
    December 10, 2009

    This thread is only three comments old and already threatening to go off-topic… oh, well.

    David:

    No rh in German (except in Greek words, in which a vowel follows it)

    What about the river Rhein (the Rhine in English); does that name have origins in Greek?

  5. #5 Gareth Simkins
    December 10, 2009

    Hi Darren,
    Good to meet you at the event – and an excellent write up, as usual.

    I asked the question about the current tropical distribution of caecilians, and was told that it was related to them being Gondwanan in origin. That answer did not really satisfy me.

    South America, Africa and India have been attached to the former Laurasian plates for quite a while – plenty of time for caecilians evolve some hardiness to cooler climates and to expand their distribution. The other amphibians are globally distributed – so why no caecilians crawling through the soils of England or Canada?

  6. #6 Darren Naish
    December 10, 2009

    Hi Gareth – it was good to see you there, I wanted to apologise for dashing off without saying goodbye, but I hope you noticed that people were disappearing for the meal and I was worried about being left behind. As for your question… I’ll leave someone else to provide an answer :) It seems to me that – for whatever reason – caecilians just haven’t been able to ‘evolve around’ the climatic, biophysical and ecological problems associated with life in cooler climes. Incidentally, there are similar constraints elsewhere in amphibian distribution: there are no caudates in the tropics, for example (with the exception of one plethodontid clade).

  7. #7 ENT-TT
    December 10, 2009

    So that asteroid monster from Empire Strikes Back is essentially a giant caecilian (with bat-worms)?

    http://www.thiel-a-vision.com/wp-content/uploads/2009/10/spaceslug.jpg

  8. #8 Gareth Simkins
    December 10, 2009

    No need to apologise, in the slightest Darren, I quite understand.

    Whoever knew that George Lucas was a herpetologist? ;-)

  9. #9 Jerzy
    December 10, 2009

    Ah, travel around the islands of Indonesia or Philippines and search for caecilians – surely every islet should have endemic undiscovered species…

    just dreaming :D

  10. #10 Bill
    December 10, 2009

    Can I just say – awesome! Thanks for the report back, and I love Tet Zoo. A happy place for zoology nerds :)

  11. #11 Andreas Johansson
    December 11, 2009

    What about the river Rhein (the Rhine in English); does that name have origins in Greek?

    Originally Gaulish, but the Romans for some reason took to writing it as if Greek, and modern European languages follow suit.

  12. #12 David Marjanović
    December 11, 2009

    the Romans for some reason took to writing it as if Greek

    Actually, is there any chance the r was voiceless? In modern Welsh, word-initial r is voiceless and is therefore written with an h behind it. The same (with “on top of” instead of “behind”) was apparently true of Ancient Greek (not of Modern Greek, however).

  13. #13 Andreas Johansson
    December 11, 2009

    I suppose it’s possible, but AFAIK Gaulish isn’t supposed to have had a voiceless rhotic. The voiceless rh of Welsh is not a common Celtic inheritance and would be unrelated.

    It does occur to me that the Romans might have got the word not directly from the Gauls but via the Greeks of Massilia, which could explain the Greekly spelling. But learned affectation seems just as likely – that’s apparently what happened to Rhaetia (Raetia on local monuments).

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