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Monitor musings, varanid variables, goannasaurian goings-on… it’s about monitor lizards

The views expressed are those of the author and are not necessarily those of Scientific American.


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There’s been a bit of a monitor lizard thing going on here for the past few months: articles have covered Australian goannas, the Komodo dragon Varanus komodoensis, Dumeril’s monitor and Timor and Peachthroat monitors, and the ‘prasinoid’ tree monitors.

Current version of the monitor montage. Image by Darren Naish.

In ‘spare’ time, I’ve been working on the montage you see here, designed to depict a reasonable amount (though not all) of extant varanid diversity. I’m going to release it as a t-shirt design and see what happens. What’s new in the world of varanids? The 2013 discovery of a new (small) Komodo dragon population at Mbeliling Forest on Flores is interesting and has been well reported in the news. It suggests that the species is more widespread across Flores than otherwise thought, and it’s also neat since it means that ‘undiscovered’ populations might persist elsewhere. Note, however, the Mbeliling Forest is still in the West Manggarai region in the far west of Flores, and not all that far away from other population centres for the species.

Pilbara rock monitor (note the large, grey ocelli and banded tail). Image (c) Stephen Zozaya.

Another recently named Aussie goanna: Bush's monitor (V. bushi), named in 2006, endemic to the Pilbara region, and previously included within V. caudolineatus. Image (c) Stephen Zozaya.

What about new species? A Western Australian goanna population, previously included within the Pilbara rock monitor V. pilbarensis, has just been raised to species level by Brad Maryan and colleagues, and named V. hamersleyensis (Maryan et al. 2014). The latter is much darker than V. pilbarensis proper, and has small white ocelli and a mostly unbanded tail (as opposed to large grey ocelli and a banded tail). The distinction is also reflected in range and genetics. What is that now – 77 named extant monitor species? And more to come…

Another tree monitor montage. Canopy goanna (V. keithhornei) shown at bottom. Images by Darren Naish.

In February 2014, I wrote an article about tree monitors, and of the several species included within that group I mentioned the very poorly known V. bogerti and V. telenesetes. André Koch and colleague have just published (April 2014) a new analysis of these species that covers their morphology, systematics and historical biogeography (Koch et al. 2014). While they express doubts about the validity of V. telenesetes (it’s known only from a single specimen), they still find it to be distinct and urge the need for further work. They also report another specimen of V. bogerti (collected on Fergusson Island in 2002), the first collected in more than 70 years. Seven specimens of this taxon are now known.

In other news, monitors are diurnal predators, right? Well, tell that to the Black-palmed monitors V. glebopalma that have been discovered moving around and feeding on prey animals during the night. As documented by Rhind et al. (2013), various observations indicate crepuscular or nocturnal behaviour in this species, and in fact assorted anecdotes and observations suggest that quite a few other monitors might forage during dusk, twilight or night as well. Further study is needed to see how important this behaviour is, and whether it’s reflected in eye anatomy, physiology, energetics or ecology.

Three of (arguably) the most unusual monitors. Clockwise from top left: V. dumerilii, V. rudicollis, V. komodoensis. Image by Darren Naish.

Finally on new studies, Matsubara et al. (2014) have just published their analysis of chromosomal sex determination in monitors. Monitors are known to have specialised sex-determining chromosomes, but this was previously only known for four species. The new study expands this so that we have data on species from additional lineages. Monitors have ZZ/ZW sex chromosomes (where females are heterogametic, not males), and the new data indicates that this was likely the ancestral condition for the group. A question for people who know more about this than I do: was the ZZ/ZW system so-named merely to give different ‘code’ letters (versus XX/XY) to a system where the ovum is heterogametic? I’ve never seen this properly explained.

In a previous article I wrote briefly about Dumeril’s monitor V. dumerili, and one of the things I said about it is that “its teeth are blunt and peg-like”. This is a statement that’s been repeated several time in the literature and I’ve never had the opportunity to check it. Turns out that it’s not true. Derek Larson of the University of Toronto (I know him best for his work on theropod teeth) kindly send me the images you see below: clearly, the teeth of Dumeril’s monitor are not blunt or peg-like, though they do seem seem to be less recurved and less blade-like than the teeth of species with a more ‘conventional’ varanid dentition. Derek is working on varanid ecomorphology and the relationship between tooth form and diet in these lizards; I look forward to hearing more about his work.

Skull and mandibles of Dumeril's monitor (specimen YPM R 11038, Peabody Museum). Images by Derek Larson, used with permission.

In the next Tet Zoo article on varanids, I’ll be talking at length about a geographically widespread group that has a significant presence across the Asian tropics, and which is of major importance as goes human economy and the region’s ecology. The monitors concerned might be excellent examples of what we term ‘ecosystem service providers’.

Finally, a world conference on monitors is planned for July 2015 and will happen in Bangkok. I somehow doubt that I’ll be attending but, if you’re seriously interested in varanids, you’ll definitely want to be there. Oh, if you’re interested in keeping up with monitor news, do always keep an eye on the open-access journal Biawak. Thanks to Stephen Zozaya and Derek Larson for some of the images used here.

Oh, here's a Perentie (Varanus giganteus), included simply because Perenties are awesome. Image (c) Stephen Zozaya.

For previous Tet Zoo articles on monitors, see…

Refs – -

Koch, A., Nicole, E., Eidenmüller, B. & Kraus, F. 2014. New data on the rare Varanus bogerti Mertens, 1950 and V. telenesetes Sprackland, 1991 (Squamata: Varanidae), two endemic monitor lizard taxa from island groups off southeastern New Guinea. The Herpetological Journal 24, 111-122.

Maryan, B., Oliver, P. M., Fitch, A. J. & O’Connell, M. 2014. Molecular and morphological assessment of Varanus pilbarensis (Squamata: Varanidae), with a description of a new species from the southern Pilbara, Western Australia. Zootaxa 3768, 139-158.

Matsubara, K., Sarre, S. D., Georges, A., Matsuda, Y., Marshall Graves, J. A. & Ezaz, T. 2014. Highly differentiated ZW sex microchromosomes in the Australian Varanus species evolved through rapid amplification of repetitive sequences. PLoS ONE 9(4): e95226. doi:10.1371/journal.pone.0095226

Rhind, D., Doody. J. S., Ellis, R., Ricketts, A., Scott, G., Clulow, S. & McHenry, C. 2013. Varanus glebopalma (Black-palmed monitor). Nocturnal activity and foraging. Herpetological Review 44, 687-688.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. irenedelse 8:43 am 05/9/2014

    was the ZZ/ZW system so-named merely to give different ‘code’ letters (versus XX/XY) to a system where the ovum is heterogametic?

    Not merely for that reason. The chromosomes governing sex differentiation have different characteristics in each system. In the XX/XY system, the male-defining chromosome, Y, is smaller and contains less genes than its X counterpart. In the ZZ/ZW system, the chromosome associated to the female sex, W, is the smaller one.

    There are other differences too: for instance, in addition to the Z and W chromosomes, temperature during incubation can play in a part in sex determination in several species of sauropsids, with examples in lizards, turtles, birds, crocodilians and the tuatara. (It was also – spoilers ahead! – a plot point in the book Jurassic Park, although for some reason, the author ascribed it to the use of frog DNA to complement the imperfectly pieced-together dinosaur genes. Which doesn’t make much sense in the birds-as-dinosaurs context that is now familiar. Crichton’s scientists might as well have used DNA from extant archosaurs instead of going as far as amphibians if they had holes to patch in their chromosomes. But of course the book was written, what, 25 years ago?)

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  2. 2. Surroundx 11:00 am 05/9/2014

    Could anybody in the know tell me how many varanid species are only known from their type collections? And whether the collection of a new specimen of V. bogerti should be considered a rediscovery of that taxon? Thanks in advance.

    Link to this
  3. 3. SciaticPain 12:42 pm 05/9/2014

    Cool montage I would buy that shirt (don’t forget to make some 2x sizes for your megafauna sized fans). I always thought your croc montage would make a good wrap-around t-shirt as well. Very interested in the monitors of Asia you allude to as ‘ecosystem service providers’. Cool Perentie.

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  4. 4. vdinets 4:53 pm 05/9/2014

    Cool drawing!
    V. griseus in Karakum Desert of Turkmenistan is largely diurnal in spring, but turns almost completely nocturnal in summer (pers. obs., not sure what happens in autumn).

    Link to this
  5. 5. Allen Hazen 4:29 am 05/10/2014

    I don’t remember the letters used (I think X and Y were two of them), but there is one context in which you HAVE to have different letters for male “dominant” and female “dominant” systems of chromosomal sex determination: an article in “Nature” (possibly “Science,” but I think “Nature”) back in the mid-to-late 1980s reported a species of fish (from some part of South America) whose chromosomal sex-determination system had THREE kinds of chromosomes: a female-producing X, a male-producing Y (which “outranks” the X in individuals with XY, as in the mammalian system), and a female-producing W (which outranks the Y in individuals with YW, as in the avian system). And reported that in wild populations all five of the permissibly combinations occurred: XX females, XY males, YY males, XW females, and YW females: no WW, because it would necessitate inheriting a paternal W.

    Moral: you THOUGHT sex was complicated, but it’s more complicated than you thought!

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  6. 6. irenedelse 5:59 am 05/10/2014

    @ Allen Hazen:
    The fish in question is a species of platyfish, Xiphophorus maculatus. The precise references are in Schartl, 2004, “A comparative view on sex determination in medaka”, Mechanisms of Development, Vol. 121(7), in part 4 of the article.

    The sex chromosomes seem to have evolved very messily in vertebrates!

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  7. 7. naishd 6:15 am 05/10/2014

    Thanks for great comments so far, much appreciated.

    Surroundx (comment # 2): regarding which extant varanids are known from their type specimens only, note that even those where only a single specimen has been deposited in a collection (e.g., V. caerulivirens and, I think, V. cerambonensis, V. finschi, V. macraei, V. melinus and V. doreanus) are known from other specimens that have been seen live (often in the pet trade). There are quite a few species known from only two or three or four specimens (e.g., V. juxtindicus, V. mabitang). Anybody know how many V. olivaceus specimens are present in collections? Might just be the holotype. Likewise for V. kingorum, perhaps. This is not meant to be a complete list, more of a discussion… I’d have to spend a long while trawling through the primary literature for better answers.

    As for whether the new specimen of V. bogerti represents a ‘rediscovery’ – I don’t think so, because (so far as I know) nobody ever thought that it might be extinct; it was just regarded as rare and under-sampled (and, indeed, it remains so).

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  8. 8. irenedelse 8:54 am 05/10/2014

    One thing I find fascinating, is the variety of markings on lizards. Here in monitors, you have species with striking geometrical patterns (like that perentie or the Pilbara rock monitor) and others where the body is basically of a solid colour (Bush’s monitor, Komodo dragon). There certainly must be a link with the animal’s environment and its way of life. Camouflage, for instance. Do perenties pose as dead trees trunks and Komodo dragons as rocks? Half serious question…

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  9. 9. markh22 5:19 pm 05/10/2014

    excellent monitor montage, Darren – keep the Varanid oriented articles coming! The explosion of recognised monitor species (and sub-species) over the last decade or so fully justifies the word count devoted to the group…..not to mention the general fascinating / varied behaviour and lifestyles of monitors overall.
    I’ll take a stab that the ‘ecosystem service providers’ you refer to might be the salvator complex? Can’t offhand think of another species that is widespread enough to be that impactful……but I’m happy to stand corrected!

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  10. 10. DavidMarjanovic 8:44 pm 05/10/2014

    was the ZZ/ZW system so-named merely to give different ‘code’ letters (versus XX/XY) to a system where the ovum is heterogametic?

    I wonder if the choice of W for the female-making chromosome was influenced by German weiblich “female”; but the chance is 50/50…

    There are other differences too: for instance, in addition to the Z and W chromosomes, temperature during incubation can play in a part in sex determination in several species of sauropsids

    Not in addition. Each species has either XX/XY or ZW/ZZ or temperature-based sex determination (which can go either way – higher temperatures make males in some, females in others); all of these seem to have evolved several times. There’s also at least one rodent species where males are X0, and then there’s the platypus.

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  11. 11. naishd 6:29 am 05/11/2014

    mark22 (comment # 9): good work, I am indeed talking of the ‘salvator complex’ monitors.

    Thanks to all for comments on sex chromosomes. Such a complex topic.

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  12. 12. irenedelse 9:37 am 05/11/2014

    Each species has either XX/XY or ZW/ZZ or temperature-based sex determination (which can go either way – higher temperatures make males in some, females in others); all of these seem to have evolved several times.

    Aren’t there a few species where temperature-dependant sex determination happens in addition to the action of sex-determining chromosomes? Schartl, 2004, mentions the Nile tilapia (which has XX/XY chromosomes), but IIRC it can also happen in an Australian skink.

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  13. 13. naishd 12:12 pm 05/11/2014

    I thought I’d heard that Sphenodon has both temperature-dependent and chromosomal sex-determination… but, nope, it’s TSD alone (albeit the rare ‘IB’ form where males occur above 21-23 deg C and females below).

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  14. 14. irenedelse 2:14 pm 05/11/2014

    This is the lizard I was looking for: a scincid, Bassiana duperreyi. “Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard”, by Radder et al., Biology Letters, 2008. In this lizard,

    offspring sex is determined by heteromorphic sex chromosomes (XX–XY system) in most natural nests, but sex ratio shifts suggest that temperatures override chromosomal sex in cool nests to generate phenotypically male offspring even from XX eggs. We now provide direct evidence that incubation temperatures can sex-reverse genotypically female offspring, using a DNA sex marker.

    The whole text is available on line. They also mention similar observations on an agamid, Pogona vitticeps. Cf. Quinn A.E, Georges A, Sarre S.D, Guarino F, Ezaz T, Graves J.A.M (2007) “Temperature sex reversal implies sex gene dosage in a reptile”. Science 316:411

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  15. 15. irenedelse 2:16 pm 05/11/2014

    (Sorry, format fail. The whole second paragraph is a quote. Sigh.)

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  16. 16. Andreas Johansson 3:20 pm 05/11/2014

    SciaticPain wrote:
    Cool montage I would buy that shirt (don’t forget to make some 2x sizes for your megafauna sized fans).

    So what sex are XXL t-shirts? :p

    (I incidentally sorta object to XXL being considered megafaunal. Some of my shirts are that nominal size, yet I’m below avg weight for Swedish men.)

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  17. 17. Allen Hazen 7:05 pm 05/11/2014

    Irenedelse–
    Thanks for filling in on my post and giving reference: I was writing from vague memories of something I’d read one afternoon while hiding from my own colleagues in the zoology library!

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  18. 18. Dartian 2:40 am 05/12/2014

    David:
    There’s also at least one rodent species where males are X0

    I presume that you’re referring to the creeping vole Microtus oregoni?

    Incidentally, XO males – and females – are also found in the Transcaucasian mole vole Ellobius lutescens and the Ryukyu spiny rat Tokudaia osimensis. In fact, these two species lack the Y chromosome altogether!

    On the other hand, in yet two other species of rodent, the wood lemming Myopus schisticolor and the collared lemming Dicrostonyx torquatus, there are XY females.

    So yeah, when it comes to sex chromosomes, there’s some quite bizarre shit out there in the rodent world. For further details, see

    Fredga, K. 1988. Aberrant chromosomal sex-determining mechanisms in mammals, with special reference to species with XY females. Philosophical Transactions of the Royal Society of London B 322, 83-95

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  19. 19. Tayo Bethel 4:42 am 05/12/2014

    About the colours and patterns in lizards:
    Keepin mind that what a lizard seesand what a mammalsees aren’t necessarily the same thing. If memory serves, many sauropsids have vision that extends into the UV spectrum. How much work has been done on the squamate visual range? Iwould guess that sexualselection has a lot to do with howcolourful lizardsare.

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  20. 20. DavidMarjanovic 7:17 am 05/12/2014

    “Genetic evidence for co-occurrence of chromosomal and thermal sex-determining systems in a lizard”

    Oh, wow. Awesome. Well, that explains how one can evolve into the other. :-)

    (Sorry, format fail. The whole second paragraph is a quote. Sigh.)

    Like Google/Blogspot, SciAm hasn’t considered the idea that people might like to have a discussion in a comment thread and doesn’t allow the <blockquote> tag. I resort to italics.

    I presume that you’re referring to the creeping vole Microtus oregoni?

    If you say so, I probably am. I can’t remember. :-)

    [...] So yeah, when it comes to sex chromosomes, there’s some quite bizarre shit out there in the rodent world.

    Impressive; but then, there are tetraploid rodents, so rodents are perhaps generally no stranger to chromosomal weirdness. I wonder about bats now; they’re diverse enough that such things might have happened just statistically. All I know is that species where all the adult males lactate…

    Iwould guess that sexualselection has a lot to do with howcolourful lizardsare.

    Definitely. Keep in mind that most vertebrates have four colour receptors, while most placental mammals have only retained two.

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  21. 21. irenedelse 8:08 am 05/12/2014

    @ Allen Hazen:
    Hiding in zoology? Awesome. ;-)

    @ DavidMarjanovic:
    Thanks for the format help. The idiosyncratic websites that allow some of the most common tags (italics, urls) but not others can be tricky.

    Well, that explains how one can evolve into the other.

    That’s what the authors seem to think too: hints at evolution of sex determination systems in amniotes. Fascinating stuff.

    If memory serves, many sauropsids have vision that extends into the UV spectrum.

    According to my own hazy memory, it’s been studied in birds, some of whom have UV reflective plumage that play a part in sexual dimorphism, courtship, etc.

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  22. 22. ekocak 8:33 am 05/12/2014

    Another thing to keep in mind with regards to lizard coloration: Many lizards, monitors included, have brightly colored or highly patterned juveniles which lose that coloration as they mature. Nile monitors for example, are born as striped black and yellow animals. I think even komodos have some kind of patterning if I remember right. My guess would be that this might have to do with filling different ecological roles from adults.

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  23. 23. irenedelse 1:48 pm 05/12/2014

    With the bad news we’ve been hearing recently about climate change, I wonder if the range of varanids and other tropical adapted reptiles will creep into the high latitudes as average temperatures go up…

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  24. 24. BrianL 4:15 pm 05/12/2014

    @irenedelse:
    With warming climates in mind, just think of all those sauropsids in the pet trade in those higher latitudes. Released or escaped pets surviving, breeding and establishing naturalised populations are probably increasingly possible. This possibility would extend to varanids and perhaps ever more so as their captive numbers increase.

    Are there any species of sauropsid moderately common in the pet trade that are particularly likely to be potential candidates for establishing naturalized populations in say northwestern Europe?

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  25. 25. naishd 4:28 pm 05/12/2014

    Re: escaped pet reptiles and their possible ecological impact, see the following…

    Soler, J. & Martínez-Silvestre, A. 2013. Feral monitor lizards (Varanus spp.) in Catalonia, Spain: an increasing phenomenon. Biawak 7, 21-24.

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  26. 26. irenedelse 5:42 pm 05/12/2014

    Are there any species of sauropsid moderately common in the pet trade that are particularly likely to be potential candidates for establishing naturalized populations in say northwestern Europe?

    Well, there’s already the case of the feral populations of red-eared terrapin (Trachemys scripta elegans)… It’s a serious problem in Europe, and probably in other parts of the world. Here, feral terrapins compete with the European pond turtle, already in trouble from loss of habitat. And they brought their diseases and parasites with them.

    @ Darren:
    Impressive. I knew about feral varanids living in the south of the USA, but Catalonia is another story. For one thing, there are real winters there, though milder than in, say, England. So far, from the Soler et al. article, monitor lizards have not yet been able to live year-long in Spain, but they can reproduce and create trouble enough for the local wildlife.

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  27. 27. irenedelse 7:44 pm 05/12/2014

    Oh, and if we consider non-reptilian sauropsids, there are of course colonies of feral parakeets in western Europe, notably the Rose-ringed Parakeet (Psittacula krameri). They are in England, France, Germany, the Netherlands… Not bad, for birds from the tropics.

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  28. 28. BrianL 3:50 am 05/13/2014

    @irenedelse:
    I should have specified non-avian sauropsids, because birds are in a different league in terms of naturalized populations. As for *Psittacula krameri*, do note that tropical though many of its populations might be, this is a bird that occurs into the foothills of the Himalayas and other more temperate regions. While not exactly a species primarily of temperate climes, characterising it as tropical is misleading. Though, from my own experience, it is a very unusual sight to see these very green parrots land and walk on ice to get a drink as I saw one do over here in the Netherlands one time!

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  29. 29. Chabier G. 4:19 am 05/13/2014

    I don’t trust a lot in Spanish winters to stop tropical reptile invaders. Some years ago we receive a subadult Pyxidea mouhoti at the Rescue Center. We didn’t have facilities to keep properly a turtle needing a constant temperature of 35ºC during day and 25ºC at night all year round, we simply left it outside, in the Mediterranean Tortoises enclosure. Well, this Cambodian Rainforest dwelling reptile did hibernate during 3 years like its European counterparts, without any health problem. Unfortunately, the experiment finished when somebody entered the Center at night and stole all the tortoises (5 species of terrestrial tortoises but he/they didn’t take any of the Red Eared Sliders).
    I think that, if many tropical reptiles can hibernate during dry seasons, they can do the same in mediterranean winters.

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  30. 30. Jerzy v. 3.0. 5:26 am 05/13/2014

    @reptiles and introductions
    In Europe, sale of red-eared slider is now banned, but ony it is replaced in pet trade by closely related subspecies and species.

    There are also introduced populations of several Mediterranean lizards. Some I would see as benign or beneficial (simply hobbyists replacing natural factors like floods in transport reptiles), but transporting eg. East Mediterranean species to Western Europe is not.

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  31. 31. markh22 6:07 am 05/13/2014

    Bit more on this (potential naturalisation of non-native species) – I seem to recall the late Bert Langewerf reporting some years back of escaped Tegu lizards that over-wintered successfully for years at his (U.S.) Georgia reptile breeding facility…..hibernating in some instances for 6 or 7 months a year. Bert maintained his adult Tegus outdoors, only intervening during hibernation (moving the animals indoors) if the temperature went below freezing for several days….but the success of at least some of the escapees shows that even this may not have been necessary. I believe that juveniles were also discovered to have over-wintered successfully. Bert felt that a few months of consistent and sufficiently warm weather in summer was the key – which matches my own experience maintaining slider turtles outdoors (in greenhouses) in the UK successfully for many years.

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  32. 32. Dartian 7:39 am 05/13/2014

    Chabier:
    this Cambodian Rainforest dwelling reptile did hibernate during 3 years like its European counterparts

    Markh22:
    escaped Tegu lizards that over-wintered successfully for years at his (U.S.) Georgia reptile breeding facility…..hibernating in some instances for 6 or 7 months a year

    So even some tropical sauropsid species are demonstrably capable of hibernating for long periods if necessary? Interesting. Did their ancestors hibernate through the K-T boundary, I wonder? ;)

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  33. 33. ectodysplasin 11:00 am 05/13/2014

    In North America, Saniwa shows up on both sides of the K-Pg, and it’s a pretty large animal.

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  34. 34. naishd 11:08 am 05/13/2014

    For anyone, ha ha, monitoring this thread, the monitor montage is now available on a t-shirt.

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  35. 35. Heteromeles 11:23 am 05/13/2014

    I’d suggest that the real problem with climate change and migration is the “wobbly” weather, as demonstrated this last winter in the eastern US. On average, temperatures are getting warmer, but occasionally there will still be unusually severe years.

    It’s those extreme years that will decimate migrating or invasive populations. If climate change really bites down, it will be hard to differentiate between the two, but that’s beside the point. In general, species (not just reptiles) will migrate towards the poles. Unfortunately, as they do so, they’ll occasionally run into bouts of severe weather, and its those occasional bad winters and/or summers that will impede movement more than the averages.

    On a different but related topic, Sherwood and Huber in 2010 published a PNAS article on An adaptability limit to climate change due to heat stress in humans. Their hypothesis was that, in mammals, peak heat stress begins at a wet-bulb air temperature of 35oC (think 35oC and 100% humidity, or comparable). Currently, wet-bulb temperatures on the planet don’t get above 31oC for any extended period, but with an average temperature rise of 7oC or more, they will. Without air conditioning, humans can’t survive that, and with maximal warming of 10oC or more, there will be large swathes of the planet that will be too hot for humans and comparable mammals during at least part of the year, including the Sahara, Outback, India, southern China, Brazil, the Middle East, parts of Spain, and the eastern US.

    Are there comparable limits for sauropsids known? Obviously some can estivate deep underground, but are there good guides to heat stress limits somewhere?

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  36. 36. ectodysplasin 11:47 am 05/13/2014

    Worth pointing out that some monitors (*V. griseus* and *V. bengalensis*) will hibernate in winter. This isn’t directly relevant to heat stress but I thought I’d throw this into the discussion.

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  37. 37. Varanussalvator 10:05 am 05/14/2014

    Also worth noting that some exotic reptiles thought of as tropical might be more accurately seen as subtropical, or at least adapted to more extreme conditions than what we would expect for a similar species living at the Equator. In the wild, they might already have the capacity to aestivate to survive the driest or coldest times of the year – I wouldn’t be surprised if southern populations of tegu, boas, and iguanas are able to do this, same for the more northern populations of monitors and pythons that live in subtropical southern China. Similarly, Cuora / Pyxidea mouhotii lives in tropical monsoon forest, with very distinct wet and dry seasons. Perhaps this species and other reptiles found in Indochina and parts of the Indian subcontinent are capable of seeking out caves and burrows to aestivate and wait out the worst of the dry spells.

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  38. 38. Chabier G. 5:45 am 05/15/2014

    Dartian, I’ve always found very plausible the idea of lethargy saving tetrapods across the K-T. Hibernation is well widespread among Crocodilians, Squamata, Chelonians, Lissamphibia,and all mammalian major clades. The “only” problem is Birds, AFAIK, only Nuttall’s Poorwill does truly hibernate, and only some other Caprimulgidae can lapse in some kind of torpor, and perhaps, at a lesser degree, some owls. Then,supposing facultative lethargic ancestors of all the surviving avian clades should be too speculative. Perhaps Tinamou-like Proto-Ratites and Galloanserae survived scratching the ground and probing crevices in search of dormant seeds and animals. Both possibilities rely on a short period (months) of world collapse after the disaster. And I can’t imagine how corals and other marine animals could survive (indeed most of them didn’t)

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  39. 39. irenedelse 10:41 am 05/15/2014

    Both possibilities rely on a short period (months) of world collapse after the disaster. And I can’t imagine how corals and other marine animals could survive (indeed most of them didn’t)

    Alternately, even in a long winter period there could have been a few more favorable areas, depending on topology, air and marine currents, etc. These ‘micro-climates’ would only have supported a few individuals of course, especially from the bigger species, so a lot of them would have entered a downward spiral of dwindling numbers, genetic impoverishment, etc. Logically, the winners would have mostly been small bodied animals (whether mammals, lizards or feathered dinosaurs), especially in the terrestrial realm where habitat fragmentation was more of a concern. (Do we know if fish species who survived the K-Pg extinction include, for instance, big sharks?)

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  40. 40. Heteromeles 12:29 pm 05/15/2014

    Since I was just looking at corals, remember that corals don’t need reefs to survive. The Torres Strait is reportedly a great example. It has a high diversity of corals growing on rocks on sandy shallows, but no reefs to speak of. Hawaii is similar (patches of coral, but not that many reefs). Coral species can remain in refugia for quite a long time. The losers are those species that depend on reefs.

    I’d caution against going unthinkingly with the logic of small bodies. After all (to pick an extreme) hummingbirds have to hibernate every night just to avoid starving to death in their sleep. Survival’s a bit more complex than “be small and generalized.” To track back closer to our topic here, which would you to survive better, a small turtle or a large one? How about a very small croc, a medium-sized adult, or a large saltie? It’s not an easy question to answer, because the big adult crocs can last for months without a meal, but it’s not clear that the smaller ones can.

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  41. 41. irenedelse 3:26 pm 05/15/2014

    @ Heteromeles:
    Well, hummingbirds are tiny, but hardly generalists, so… ;-)
    You’re right, it’s not simply being small. Or at least, smallish, since really tiny vertebrates have their own set of problems. Being able to hibernate or stay without food for months is one obvious solution. But I was wondering about the possibilities of non-homeothermic animals surviving a scenario where the climate stayed inhospitable and the plant productivity low for more than six months. (One large croc may well subsist with fewer meals and reduced activity in such conditions, but how many could a shrunken habitat support? At least amphibious crocs would be able to follow the currents to cover large areas, find mates, etc. Big land crocs would have logically have more trouble here.) I don’t know what the current geological thinking is on how long the K-Pg winter would have lasted, I admit.

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  42. 42. Zoovolunteer 5:38 pm 05/15/2014

    Personally, I wonder if the main survivors of the larger animals like crocs might have been unhatched eggs rather than adults. I know crocs do quite a bit of nest guarding and so forth, but I would think that an unattended nest or two might provide at least a few hatchlings even if the adults were dead. Assuming the impact was at the right time of year, they could wait out several months before emerging to a now (nearly) predator-free world.

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